# Selina ICSE Class 10 Chemistry Solutions Chapter 1 Periodic Table

#### Intext – Question – 1

Question 1: a) State modern periodic law. Name the scientist who stated the law.
b) What is a periodic table? How many groups and periods does modern periodic table have?
Solution 1:
a) According to the contemporary periodic law, “the physical and chemical properties of elements are a periodic function of their atomic number.” In the beginning of 20th century, Henry Mosley (1913) rearranged periodic table after the knowledge of electron, proton and neutron.
b) A Periodic Table is a tabular arrangement, horizontal rows are called periods and vertical columns are called groups. The numbers of groups are 18 and numbers of periods are 1 to 7.

Question 2: Why sodium element of group 1 and chlorine element of group 17 both have valency 1?
Solution 2:
Valency is the combing capacity of any element. The number of electrons present in the outermost shell of an element determines the valency of that element. This property is explained by electronic configuration of elements. The outermost orbital of Group 1 elements has one electron, while the outermost orbital of Group 7 elements has seven electrons. The number of electrons in the outermost shell determines the valency or valence shell.
If the outermost shell has one electron, it can contribute one electron while interacting with other elements to achieve a stable electronic structure. If the outermost shell has seven electrons, its valency is one i.e. 8 – 7 = 1. since it may accept one electron from the combining atom. The number of electrons in the valence (outermost) shell rises from left to right in a given period. However, the valency grows only until Group 14, when it becomes 4, and then drops, becoming 1 in Group 17.

Question 3: What are horizontal rows and vertical columns in a periodic table known as?
Solution 3:
The horizontal rows are called periods and vertical columns are called groups. The numbers of group are 18 and numbers of periods are 1 to 7. The period represents main energy level ‘n’ i.e. shell or orbit.

Question 4: Periodicity is observed due to the similar ………………… .
(Number of valence electrons / atomic number / electronic configuration).
Solution 4:
Electronic configuration

Question 5: How does the electronic configuration in atoms change
(i) in a period from left to right?
(ii) in a group top to bottom?
Solution 5:
(i) The atomic size decreases on moving from left and right in a period and the value of effective nuclear change increases. Hence, the value of ionization enthalpy increases periodically from left to right in a period and cations are not easily formed.
(ii) The atomic size increase on moving from top to bottom in a group and the value of effective nuclear change decreases. Hence, the value of ionization enthalpy decreases periodically from top to bottom in a group and cations are easily formed.

Question 6: Correct the statements.
(i) Elements in the same periods have equal valency.
(ii) Valency depends upon the number of shells in an atom.
(iii) Copper and zinc are representative elements.
(iv) Transition elements are placed at the extreme right of the periodic table.
Solution 6:

(i) Elements in the same group have equal valency.
(ii) Valency depends upon the number of valence electrons in an atom.
(iii) Copper and zinc are transition elements.
(iv) Noble gases are placed at the extreme right of the periodic table.

Question 7: Name two elements in each case:

Solution 7:
(i) Alkali metals
Name of Elements:- Sodium and potassium
(ii) Alkaline earth metals
Name of Elements:- Calcium and magnesium
(iii) halogens
Name of Elements:- Chlorine and bromine
(iv) Inert gas
Name of Elements:- Neon and Argon
(v) Transition element
Name of Elements:- Iron and Cobalt
(vi) Lanthanides
Name of Elements:- Cerium and Europium
(vii) Actinides
Name of Elements:- Uranium and Neptunium

Question 8: What do you understand by?
(i) Periodicity:
(ii) Typical elements:
(iii) Orbits:
Solution 8:

(i) Periodicity:- Periodic qualities are properties that return at regular intervals or have a progressive variation at regular intervals, and the phenomenon is known as periodicity of elements. Periodic change in the properties of element depends on electronic configuration of elements.
(ii) Typical elements:- The third period elements, Na, Mg, Al, Si, P, and Cl, are known as typical elements because they summaries the attributes of their respective groups. The elements in the periodic table with set oxidation states are known as typical elements.
(iii) Orbits:- The electron around the nucleus revolves only in certain fixed circular path of fixed radius and energy. These circular path are also known as orbits, stationary states or allowed energy states or energy shells.

Question 9: Why are noble gases placed in a separate group?
Solution 9:

Noble gases have completely filled orbitals in the valence shell and are very stable, it becomes very difficult to alter their stable arrangement by the addition or removal of electrons. Thus they exhibit very low chemical reactivity. So that’s why noble gases placed in a separate group.

Question 10: Name two elements you would expect to show chemical reactions similar to calcium. What is the basis of your.
Solution 10:
Beryllium and magnesium will have chemical interactions that are similar to those of calcium. Because these elements, like calcium, belong to the same group 2 and have two electrons in their outermost shell.

Question 11: Name the metal(s) and non-metals in the first twenty elements.
Metals:
Non-metals:
Solution 11:

Question 12: Name the type of elements, which have their:
(i) Outermost shell complete – ………………..
(ii) Outermost shell incomplete – ………………
(iii) two outermost shell incomplete – ………………
(iv) one electron short of octet – ……………………
(v) two electrons in the outermost orbit – ……………
Solution 12:
(i) Outermost shell complete – Noble gases
(ii) Outermost shell incomplete – Representative elements
(iii) two outermost shell incomplete – Transition elements
(iv) one electron short of octet – Halogens
(v) two electrons in the outermost orbit – Alkaline Earth metals

Question 13: An element has 2 electrons in its N shell.
(i) What is its atomic number?
(ii) State its position in periodic table
(iii) Is is metal or non-metal?
(iv) State the name assigned to this group?
Solution 13:
(i) Its atomic number is 30.
(ii) It belongs to the 12th group and the 4th period.
(iii) Metal.
(iv) IIB is the term given to this group.

Question 14: State the valency of the elements of periods 3 and write the formula of their oxides.
Solution 14:
(i) Element: Na
Valency: 1
Formula of Oxides: Na2O
(ii) Element: Mg
Valency: 2
Formula of Oxides: MgO
(iii) Element: Al
Valency: 3
Formula of Oxides: Al2O3
(iv) Element: Si
Valency: 4
Formula of Oxides: SiO2
(v) Element: P
Valency: 5
Formula of Oxides: P2O5
(vi) Element: S
Valency: 2
Formula of Oxides: SO2
(v) Element: CI
Valency: 1
Formula of Oxides: Cl2O

Question 15: An element A has atomic number 14. To which period does this element belong and how many elements are there in this period.
Solution 15:
It is belong to period three and eight elements are there.

Question 16: Answer the following in respect of element 31/15𝐏
(i) Give its electronic configuration
(ii) To which group and period does it belong?
(iii) What is its valency?
(iv) Is it a metal or non – metal
(v) Is it a reducing agent or oxidizing agent?
(vi) Give its formula with chlorine.
Solution 16:

(i) Electronic configuration of P: 2, 8, 5
(ii) 15th Group and 3rd Period
(iii) Valency of P = 8 – 5 = 3
(iv) Phosphorus is a non-metal.
(v) It is an oxidizing agent.
(vi) Formula with chlorine = PCl3

#### Intext – Question – 2

Question 1: Name any five periods properties.
Solution 1:
(i) Electron affinity
(ii) Atomic size
(iii) Metallic character
(iv) Non-metallic character
(v) Ionization energy

Question 2: What do you understand by atomic size? State its unit.
Solution 2:
Atomic size is a measurement of distance of the outermost shell from nucleus of an atom. Angstrom and Picometre are the units of measurement.

Question 3: Give the trends in atomic size on moving:
(i) down the group
(ii) across the period right to left.
Solution 3:
(i) As we travel from right to left in a period, the atomic size of an atom grows as we go down a group from top to bottom.
(ii) As we move from right to left in a period, the atomic size of an atom increases.

Question 4: Arrange the elements of second and third periods in increasing order of their atomic size.
(i) Second Period
(ii) Third Period
Solution 4:
Second Period: Fluorine < Neon < Oxygen < Nitrogen < Carbon < Boron < Beryllium < Lithium.
Third Period: Chlorine < Argon < Sulphur < Phosphorus < Silicon < Aluminum < Magnesium < Sodium.

Question 5: Why is the size of (i) neon greater than fluorine? (ii) sodium is greater than magnesium?
Solution 5:
(i) Neon has a larger size than fluorine because the outer shell of neon is complete (octet). As a result, the effect of nuclear attraction on electrons in the valence shell is invisible.
(ii) Because magnesium has a higher atomic number than sodium but the same number of shells, its nuclear pull is greater.

Question 6: Which is greater in size?
(i) an atom or a cation
(ii) an atom or an anion
(iii) Fe2+ or Fe3+
Solution 6:
(i) Because a cation is formed by the loss of electrons, protons in a cation are always more than electrons. As a result, the nucleus attracts and pushes electrons inward.
(ii) Because an anion is formed by the gain of electrons, which implies there are more electrons than protons, it is bigger than an atom. There is less inward pull because the nucleus’ effective positive charge is smaller. As a result, the size of the object grows.
(iii) Because an anion is formed by the gain of electrons, which implies there are more electrons than protons, it is bigger than an atom. There is less inward pull because the nucleus’ effective positive charge is smaller. As a result, the size of the object grows.

Question 7: Metallic character and non-metallic character are periodic properties discuss.
Solution 7:
The tendency of forming cation by loosing electron from an atom of element is called its metallic property. For example, Alkali metals of Group 1 are called most electropositive elements because these elements form cation by loosing electrons easily. These elements are mostly metallic in nature. These elements have most metallic properties.
The tendency of forming anion by gaining electrons by an atom of an element is called its non-metallic property. For example, the elements of halogen family, i.e. Group 17 form anion by gaining electrons easily. So, group 17, elements are mostly non-metallic in nature.

Question 8: Give the trend in metallic character:
(i) across the period left to right,
(ii) down the group top to bottom.
Solution 8:
(i) As we move from left to right in a period, the metallic character diminishes.
(ii) As we move down a group, it gets higher.

Question 9: State the trends in chemical reactivity:
(i) across the periods left to right
(ii) Down the group
Solution 9:
(i) The chemical reactivity of elements reduces and then increases over time.
(ii) As the potential to lose electrons increases down the group, chemical reactivity increases

Question 10: State the trends in physical properties on moving down the group. Give an example to illustrate.
Solution 10:

Metal’s melting and boiling points decline as they progress through the group. Consider the following table, which shows the trend in group 1 elements: Below table shows, m.p. and b.p. drop from Li to K.

As you move down the group, the melting and boiling points of non-metals rise. Example: Examine the following table for the trend in Group 17 elements:

From the above table, it is clear that m.p. and b.p. increase from F to I.

Question 11: An element X belong to 4th period and 17th group, state.
(i) No of valence electrons in it
(ii) Name of the element.
(iii) Name the family to which it belong.
(iv) Write the formula of the compound formed when it reacts with 27/13𝐲
Solution 11:

(i) The outermost shell of an element in the 17th group has 7 electrons.
(ii) The element’s name is bromine.
(iii) Bromine is a member of the halogen family.
(iv) The element 27/13Y has three electrons available for donation in its outermost shell; thus, its valency is three. Bromine has a valency of one, whereas fluorine has a valency of one. To achieve the stable electronic configuration, 27/13Y can contribute three electrons and bromine can take one electron. As a result, the compound’s formula is AlBr3.

Question 12: The given table shows elements with the same number of electrons in its valence shell.

State:
(i) Whether these elements belong to same group or period.
(ii) Arrange them in order of increasing metallic character.
Solution 12:
(i) These elements are from the same family, although they are not from the same time period.
(ii) We know that m.p. reduces as the group size decreases. As a result of the aforementioned table, the items can be sorted by period as follows:
Elements B C A
m.p. 180.0 97.0 63.0
As one travels along the group, the metallic character becomes more prominent. As a result, the following is the order of the elements with increasing metallic character: B, C and A

#### Intext – Question – 3

Question 1: (a) Define the term ‘ionisation potential’
(B) Represent in the form of an equation. In which unit it is measured?
Solution 1:
(a) Ionisation enthalpy or ionization potential is defined as the amount of energy required to remove an electron from the valence shell of the isolated gaseous atom of the element to convert the atom into the gaseous cation.
Neutral atom (g) + Ionisation enthalpy → Cation (g) + e-
It is measured in kcal/mole or KJ/mole or eV/mole. Since, the energy is required in this process, so its value is always positive. Its S.I unit kJmol-1.

Question 2: What do you understand by successive ionization energies?
Solution 2:
The energy required to remove one more electron from the cation is called second ionization energies or successive ionization energies. In other words successive ionisation energy is the amount of energy required to eliminate the remaining electrons one by one.

Question 3: State the trends in ionization energy:
(a) across the period:
(b) down the group.
Solution 3:
(a) It is difficult to remove an electron from an atom on moving left to right in a period. It is due to (i) decrease in atomic size (ii) increase in value of effective nuclear charge. Hence, the value of ionization enthalpy increase on moving left to right in a period or across the period.
(b) It is easy to remove an electron from an atom on moving top to bottom in a group. It is due to (i) increase in atomic size (ii) decrease in value of effective nuclear charge. Hence, the value of ionization enthalpy decreases on moving up to down in a group.

Question 4: Name the elements with highest and lowest ionization energies.
Solution 4:
Helium has highest and lowest ionization energies. The ionization energy decrease from top to bottom in groups and increases from left to right across a period.

Question 5: Arrange the elements of second and third period in increasing order of ionization energy.
Solution 5:
Second period: Neon > Fluorine > Oxygen > Nitrogen > Carbon > Boron > Beryllium > Lithium
Third Period: Argon> Chlorine > Sulphur > Phosphorus > Silicon > Aluminum >Magnesium > Sodium

Question 6: (a) Define the term ‘electron affinity’.
(b) Arrange the elements of second period in increasing order of their electron affinity. Name the elements which do not follow the trend in this period.
Solution 6:
(a) Electron gain enthalpy or electron affinity of an element is defined as the amount of energy released when on electron is added to the valence shell of an isolated gaseous atom of that element, to convert the atom into a gaseous anion.
Second period: Lithium < Boron < Carbon < Oxygen < Fluorine,
Neon, Nitrogen and Beryllium do not follow the trend.

Question 7: State the factors on which electron affinity depends.
Solution 7:
Electron affinity depends on:
(a) Nuclear charge
(b) Atomic size

Question 8: Electron affinity values generally across the periods left to right and down the group top to bottom.
Solution 8:
(i) Increases
(ii) Decreases

Question 9: Give reason:
(a) Electron affinity of halogens is comparatively high,
(b) Electronegativity of chorine is higher than Sulphur.
Solution 9:
(a) The rise in atomic number and decrease in size as we move from left to right results in a stronger nuclear pull. As a result, both the ability to attract electrons and the electron affinity increase.
Noble gases, on the other hand, have a complete stable octet configuration and so have a lower electron affinity than halogens.
As a result, the halogens on the far right have the maximum electron affinity in a given period.
(b) Chlorine is smaller and has a higher atomic number than sulphur. Because it has a stronger nuclear force, it has a higher electron affinity than sulphur.

Question 10: Why fluorine has higher E.N. than chorine?
Solution 10:
Fluorine has higher E.N. than chorine because chlorine is larger than fluorine, the electrons that are farther away from the nucleus feel less force of attraction, resulting in lower electron negativity for chlorine.

Question 11: Define the term ‘Electronegativity’ state its unit.
Solution 11:
Electronegativity is the property to attract shared paid of electrons in a covalent bond formed between two dissimilar atoms. The S.I. unit is Pauling unit.

Question 12: (a) Name the elements with highest and lowest electronegativity,
(b) State the character of the oxide of period 3.
Solution 12:
(a) The most electronegative element in periodic table is Fluorine(F) and lowest is Caesium.
(b) As we move from left to right in third period, the character of oxides changes from basic to acidic. As a result, sodium creates the most basic oxide, whereas aluminium oxide is amphoteric, and phosphorus, sulphur, and chlorine oxides become increasingly acidic.

Question 13: Name the periodic property which relates to the:
(a) Amount of energy required to remove an electron from an isolated gaseous atom,
(b) Character of element which loses one or more electrons when supplied with energy.
(c) Tendency of an atom to attract the shared pair of electron.
Solution 13:
(a) Ionization energy
(b) Metallic character
(c) Electronegativity

Question 14: Explain the following:
(a) Group 17 elements are strong non-metals, while group 1 elements are strong metals
(b) Metallic character of elements decreases from left to right in a period while it increases in moving down a group.
(c) Halogens have a high electron affinity.
(d) The reducing power of element increases down in the group while decreases in a period.
(e) Size of atom progressively becomes smaller when we move from sodium (Na) to chlorine (CI) in the third period of the periodic table.
Solution 14:
(a) As one moves through a period, nuclear pull increases due to an increase in atomic number, resulting in a decrease in atomic size. As a result, elements cannot easily shed electrons. As a result, strong non-metals make up Group 17, while strong metals make up Group 1.
(b) As one moves through a period, nuclear pull increases due to an increase in atomic number, resulting in a decrease in atomic size. As a result, elements cannot easily shed electrons. As a result, strong non-metals make up Group 17, while strong metals make up Group 1. The atomic size and nuclear charge both grow as you move down a group. When compared to increased nuclear charge, the effect of increased atomic size is larger. As a result, metallic nature rises as one proceeds down a group, implying that electrons can be easily lost.
(c) Halogens have a very small atomic size. The greater the electron affinity, the smaller the atomic size, because the effective attractive force between the nucleus and the valence electrons is greater in smaller atoms, holding the electrons securely in place.
(d) The reducing property is determined by the elements’ ionisation potential and electron affinity. The electron affinity and ionisation energy both rise when the atomic size drops and the nuclear charge increases in a period, from left to right in a horizontal row of the periodic table. As a result, the tendency to lose electrons reduces as the period progresses from left to right, and the reducing characteristic lowers as well. The electron affinity and ionisation potential falls from top to bottom as the group progresses. As a result, the tendency to lose electrons rises, and the reducing property rises as well, from top to bottom.
(e) An atom’s size falls from left to right during a period. This is due to the fact that the nuclear charge, or atomic number, grows from left to right with time, bringing the outermost shell closer to the nucleus. As a result, when the third period is taken into account, sodium is determined to be the largest, while chlorine is the lowest.

#### Exercise: 1

Question1 (a) How does the electronic configuration of an atom relate to its position in the modern periodic table?
(b) Write the number of protons, neutrons and electronic configuration of 39/19K, 31/15P. Also state their position in periodic table.
Solution 1:
(a) In the modern periodic table, the arrangement of elements has been made on the basis of atomic number. As number of protons in the nucleus is equal to number of electrons present in it, so this periodic table leads to electronic configuration of elements. This form of periodic table is very simple and more extended in comparison to Mendeleef’s periodic table. It is also called “extended or long form of Periodic table”.
In this periodic table, horizontal rows are called periods and vertical columns are called groups. The number of groups are 18 and number of periods are 1 to 7. The period represents main energy level ‘n’ i.e. shell or orbit. First period contains two elements. This is called very short period. Second and third period contain 8-8 elements, which are called short periods. D-orbitals are included in fourth and fifth periods. These periods contain 18-18 elements. These periods are called long periods. F-orbitals start in sixth and seven periods so these periods contain 32-32 elements. These are called very long periods, one-one parent element of f-block is shown in periodic table while 14-14 elements are shown separately in two horizontal rows. The elements of first row are called lanthanides and the elements of second row are called actinides.
(b) The number of protons in an atom equals the atomic number. As a result, the number of protons in the K atom is 19
The amount of neutrons equals the mass number multiplied by the atomic number. As a result, the number of neutrons in the K atom is 3919 = 20. The number of protons equals the number of electrons.
As a result, the number of electrons equals 19.
Furthermore, the electrical arrangement of the K atom is 2, 8, 8, 1.
Because the K atom has four shells, it belongs to the fourth period. It belongs to group 1 since it only has one valence electron.
In the P atom, there are 15 protons.
The number of neutrons in the P atom is 3115, which equals 16. P atom has a total of 15 electrons.
P atom electrical configuration = 2, 8, 5
Phosphorus belongs to period 3 since it has three shells, and with five valence electrons, it is located in the fifth plus ten group, which is the 15th group.

Question 2: Fluorine, chlorine and Bromine are put in one group on basis of their similar properties.
(a) What are those similar properties?
(b) What is the common name of this group or family?
Solution 2:
(a) Non-metals containing seven valence electrons include fluorine, chlorine, and bromine. They have a valency of one and are strongly electronegative. They exist in the form of diatomic molecules.
(b) They are known as halogens because they form ionic compounds with alkali metals. Salts are compounds that contain these elements and are defined by their ability to create salts.

Question 3: What is the main characteristic of the last element in each period of the periodic table? What is the general name of such elements?
Solution 3:
Each periodic table era ends with a gaseous element having a completely filled valence shell. The other five gases have an octet configuration, with the exception of helium, which has a complete duplet structure. The elements of Group 18 that are frequently referred to as such are known as noble gases.

Question 4: According to atomic structure, what determines which element will be the first and which will be the last in a period?
Solution 4:
The electrical configuration of an element has an impact on its place in the Modern Periodic Table. The element with one valence electron is assigned to the first group of a period, whereas the element with eight valence electrons is assigned to the 18th.

Question 5: How does the number of:
(i) Valence electrons and
(ii) Valency vary on moving from left to right in the second period of the periodic table?
Solution 5:
(i) As we move from left to right in a period, the number of valence electrons increases by one. Groups 1 and 2 have 1 and 2 valence electrons, respectively, while groups 13 to 18 have valence electrons in the group number minus 10. As a result, the valence electrons in groups 13 to 18 are 3, 4, 5, 6, 7, and 8 correspondingly.
(ii) The number of valence electrons determines valency. Valency is equal to the number of valence electrons for elements in groups 1, 2 and 13, hence their valency is 1, 2 and 3 accordingly. Because the elements in groups 14 to 17 require electrons to complete their octet configuration, they must gain electrons. The number of valence electrons in their valency is 8 minus the number of valence electrons in their valency. Their relative valencies are 4, 3, 2, and 1.

#### Question 6: Fill in the blanks:

(a) The horizontal rows in the periodic table are called ____________.
(b) On moving across a period from right to left in periodic table, the atomic size of the atom _________.
(c) On moving from right to left in the second period, the number of valence electrons_________.
Solution 6:
(a) The horizontal rows in the periodic table are called Periods.
(b) On moving across a period from right to left in periodic table, the atomic size of the atom increases.
(c) On moving from right to left in the second period, the number of valence electrons decreases.

Question 7: An element barium has atomic number 56. Look up its position in the periodic table and answer the following questions.
(a) Is it a metal or a non – metal?
(b) Is it more or less reactive than calcium?
(c) What is its valency?
(d) What will be the formula of its phosphate?
(e) Is it larger or smaller than caesium (Cs)?
Solution 7:
(a) It is a metal since it belongs to group II and contains two valence electrons.
(b) In the group, barium is placed below calcium. It is easier for it to shed valence electrons to complete its octet configuration since it has more shells. As a result, it has a higher reactivity than calcium.
(c) It requires the loss of two valence electrons to complete its octet configuration; hence its valency is also two.
(d) Its phosphate formula will be (Ba)3(PO4)2
(e) Because the size drops as we move from left to right in a period, it will be smaller than Cesium.

Question 8: How do the following change on moving from left to right in a period of the periodic table?
(a) Atomic structure (electron arrangements)
(b) Chemical reactivity of elements.
(c) Nature of oxides of the elements.
Solution 8:
(a) As we progress through any given period, the number of valence electrons grows by one. As a result, the valence electrons will grow from 1 to 7 as we progress from Lithium to Neon in Period 2.
(b) As we move from left to right, the metallic character reduces while the non metallic character grows.
Chemical reactivity of elements drops and subsequently increases as a period progress from left to right.
In period 3, for example, Sodium is the most reactive metal, Chlorine is the most reactive non-metal, and Silicon is the least reactive.
(c) In general, metal oxides are basic, while non-metal oxides are acidic. When a result, as one moves from left to right across a period, metallic strength drops while nonmetallic strength increases, the strength of basic oxides decreases while the strength of acidic oxides increases. Sodium, for example, produces a basic oxide, whereas sulphur and phosphorus produce acidic oxides.

Question 9: This question refers to the elements of the periodic table with atomic number from 3 to 18.
Some of the elements are shown by letters, but the letters are not the usual symbols of the elements.

Which of these:
(a) have most electronegative element.
(b) is a halogen?
(c) is an alkali metal?
(d) is an element with valency 4?
(e) have least ionization energy?
(f) have least atomic size in period 3.
Solution 9:
(a) Noble gases- H and P
(b) Halogens- G and O
(c) Alkali metals – A and I
(d) D and L have valency of 4
(e) I with atomic number 11.
(f) Cl has the least atomic size in period 3 with atomic number 17.

Question 10: In group I of the periodic table, three elements X,Y and Z have ionic radii 1.33 A˚, 0.95 A˚ and 0.60 A˚ respectively. Giving a reason, arrange them in the order of increasing atomic number in the group.
Solution 10:
The number of shells grows as we advance down a group, and hence the atomic size increases.
As a result, Z will have the least atomic number, followed by Y, with X having the biggest.
As a result, the elements will be Z<Y<X in order of increasing atomic number.

Question 11: How does the chemical reactivity of:
(a) alkali metals vary?
(b) halogens vary?
Solution 11:
(a) As the distance between the valence electrons and the nucleus decreases as one moves along the group, the ionisation energy decreases. Alkali metal reactivity rises from lithium to francium.
(b) As we progress down a group, the size of the atoms grows larger, making it more difficult for them to attract electrons. Halogen reactivity diminishes from Fluorine to Astatine.

Question 12: An element X belong to 3rd periods and group II of the periodic table state:
(a) the number of valence electrons,
(b) the valency,
(c) name of the element,
(d) whether it is a metal or a non-metal.
Solution 12:
(a) It has three shells, K, L, and M, because it belongs to period 3. Because it is in group II, the outermost M shell will have two valence electrons.
(b) Valency will be 2 with 2 valence electrons.
(c) It has an atomic number of 12 and an electronic configuration of 2, 8, 2, therefore X is Magnesium.

Question 13: The electronic configuration of an element T IS 2, 8, 8, 1.
(a) What is the group number of T?
(b) What is the period number of T?
(c) How many valence electrons are there in an atom of T?
(d) What is the valency of T?
(e) Is it a metal or a non-metal?
Solution 13:
(a) The Group number of T is 1, since the valence electrons is 1.
(b) T belongs to the period 4 with 4 shells.
(c) Number of electrons = 2 + 8 + 8 + 1 = 19
(d) The valency of T is 1.
(e) It is a metal, since it has one valence electron.

Question 14: Arrange the elements of group 17 and group 1 according to the given conditions.
(a) Increasing order of atomic size,
(b) Increasing non – metallic character
(c) Increasing ionization potential
(d) Increasing electron affinity
(e) Decreasing electro negativity.
Solution 14:
(a) Group 1: Lithium< Sodium< Potassium< Rubidium < Caesium< Francium
Group 17: Fluorine < Chlorine < Bromine< Iodine < Astatine
(b) Group 1: Francium
Group 17: Astatine< Iodine< Bromine< Chlorine< Fluorine
(c) Group 1: Francium< Cesium< Rubidium< Potassium< Sodium< Lithium
Group 17: Astatine< Iodine< Bromine< Chlorine< Fluorine
(d) Group 1: Francium
Group 17: Astatine
(e) Group 1: Lithium>Sodium> Potassium> Rubidium> Cesium> Francium
Group 17: Fluorine > Chlorine> Bromine > Iodine > Astatine

Question 15: Complete the following sentences choosing the correct word or words from those given in brackets at the end of each sentence:
(a) The properties of the elements are a periodic function of their _________ (atomic number, mass number, reative atomic mass).
(b) Moving across a _________of the periodic table the elements show increasing _________ character (group, period, metallic, non-metallic).
(c) The elements at the bottom of a group would be expected to show _________ metallic character than the element at the top. (less, more).
(d) The similarities in the properties of a group of elements are because they have the same ___________ (electronic configuration, number of outer electrons, atomic numbers).
Solution 15:
Complete the following sentences choosing the correct word or words from those given in brackets at the end of each sentence:
(a) The properties of the elements are a periodic function of their atomic number (atomic number, mass number, reative atomic mass).
(b) Moving across a periods of the periodic table the elements show increasing non-metallic character (group, period, metallic, non-metallic).
(c) The elements at the bottom of a group would be expected to show more metallic character than the element at the top. (less, more).
(d) The similarities in the properties of a group of elements are because they have the same number of outer electrons (electronic configuration, number of outer electrons, atomic numbers).

Question 16: Give reasons for the following:
(a) The size of the anion is greater than the size of the parent atom.
(b) argon atom is bigger than chlorine atom.
(c) Ionisation potential of the element increases across a period.
Solution 16:
(a) Anion is created when electrons gain energy. As a result, the number of electrons is greater than the number of protons. Because the nucleus’ effective positive charge is lower, there is less inward attraction. As a result, the size expands. As a result, the size of an atom is larger than that of its parent atom.
(b) Because Argon has a stable octet configuration, the influence of nuclear pull on the valence shell electrons cannot be seen due to inter- electronic repulsions, resulting in a larger size.
(c) Bromine atoms have a larger size than chlorine atoms, making it more difficult for them to attract electrons. As a result, Cl reacts faster than Br.

Question 17: Which element has:
(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 2, 8, 3?
(c) a total of three shells with five electrons in its valence shell?
(d) a total of four shells with two electrons in its valence shell?
(e) twice as many electrons in its second shell as in its first shell?
Solution 17:
(a) Neon
(b) Aluminum
(c) Phosphorus
(d) Calcium
(e) Carbon

Question 18: Name
(a) An alkali metal in period 3 and halogen in period 2.
(b) The noble gas with 3 shells.
(c) The non-metals present in period 2 and metals in period 3.
(d) The element of period 3 with valency 4
(e) The element in period 3 which does not form oxide
(f) The element of lower nuclear charge out of Be and Mg.
(g) Which has higher E.A. fluorine or Neon.
(h) Which has maximum metallic character Na, Li or K.
Solution 18:
(a) Na and F
(b) Argon
(c) C, N, O and F are non-metals present in period 2 while Na, Mg and Al are metals in period 3.
(d) Silicon
(e) Argon
(f) Mg
(g) Fluorine
(h) K

Question 19: Chorine in the periodic table is surrounded by the elements with atomic number 9, 16, 18 and 35.
(a) Which of these have physical and chemical properties resembling chlorine.
(b) Which is more electronegative than chlorine
Solution 19:
(a) Element with atomic number 9 and 35 has physical and chemical properties resembling chlorine.
(b) Element with atomic number 9 has electronegative than chlorine.

Question 20: (a) State the number of elements in periods 1, Periods 2, and Period 3, of the periodic table.
(b) name the elements in period 1.
(c) What is the common feature of the electronic configuration of the elements at the end of period 2, and period 3?
(d) if an element is in group 17, it is likely to be________(Metallic/non-metallic) in character while with one electron in its outermost energy level (shell), then it is likely to be________(Metallic / Non-metallic).
Solution 20:

(a) Period 1 has 2 elements while period 2 and period 3 have 8 elements each.
(b) Hydrogen and helium
(c) The elements at the end of period 2 and Period 3 have 8 electrons in its outermost shell.
(d) If an element is in group 17, it is likely to be Non-metallic (Metallic / non-metallic) in character while with one electron in its outermost energy level (shell), then it is likely to be metallic (Metallic / Non-metallic)

Question 21: First ionization enthalpy of two elements X and Y are 500KJ mol-1 and 375KJ mol-1 respectively. Comment about their relative position in a group as well as in a period.
Solution 21:

Position in a group: X and Y
Position in a period: Y and X

Question 22: A metal M forms as oxide having the formula M2O3. It belongs to third period. Write the atomic number and valency of the metal.
Solution 22:

Period no. = no. of shells, so n = 3 From the formula M2O3 its valency is 3.
Since it is a metal, its valence shell has 3 electrons.
So its electronic configuration is 2, 8, 3
Atomic number =13
Hence, the metal is Aluminum with valency 3.

Question 23: Explain why are the following statements not correct:
(a) All groups contain metals and non-metals.
(b) Atoms of elements in the same group have the same number of electron(s)
(c) Non- metallic character decreases across a period with increase in atomic number
(d) Reactivity increases with atomic number in a group as well as in a period.
Solution 23:
(a) Because all of the elements in a group have the same number of valence electrons, they can either contain metals or non-metals, such as alkali and alkaline metals, which only contain metals, and halogens, which are non-metals.
(b) Atoms of the same elements in the same group have the same number of valence electrons, but no two elements have the same number of electrons.
(c) Non-metals are electronegative because they have a tendency to gain electrons in order to achieve a stable configuration. The rise in atomic number and decrease in size as we move from left to right results in a stronger nuclear pull. As a result, the non-metallic feature evolves over time.
(d) Reactivity reduces at first and then grows as one moves from left to right in a period, since the tendency to lose electrons lowers initially and then increases as one moves from left to right, while the tendency to gain electrons increases as one moves from P to Cl, therefore reactivity increases. In the case of a group, reactivity grows as the tendency to lose electrons increases, whereas in the case of non-metals, reactivity reduces as the tendency to gain electrons decreases as the group progresses.

Question 24: Arrange the following in order of increasing radii:
(a) CI- , CI
(b) Mg2+, Mg, Mg+
(c) N, O, P
Solution 24:
(a) Cl < Cl¯
(b) Mg2+ < Mg+ < Mg
(c) O < N < P

Question 25: Which element from the following has the highest ionization energy? Explain your choice.
(a) P, Na, CI
(b) F, O, Ne
(c) Ne, He, Ar
Solution 25:
(a) Cl
Metals have a low ionisation energy, while non-metals have a high one. In addition, ionisation energy tends to rise over time. The third phase includes the elements P, Na, and Cl. Group 1 is Na, Group 15 is P, and Group 17 is Cl.
(b) Ne
Because of their steady electrical structure, inert gases have zero electron affinity.
(c) He
The ionisation energy drops as the atomic size decreases, i.e. as one progresses down a group. Inert gases include Ne, He, and Ar. Period 1 is He, Period 2 is Ne, and Period 3 is Ar.

#### Question 26: Choose the correct answer.

(a) An element in period 3 whose electron affinity is zero
(i) Sulphur
(ii) Sodium
(iii) Neon
(iv) Argon

Solution :

Argon

(b) An alkaline earth metal
(ii) potassium
(iii) calcium
(iv) Copper

Solution :

Calcium

(c) An element with highest ionization potential
(i) Calesium
(ii) Fluorine
(iii) Helium
(iv) Neon

Solution :

Helium

Question :
The table given below represents the first three periods. Study the table and answer the question as given below
(a) Write the formula of the sulphate of the element with atomic number 13.
(b) What type of bonding will be present in the oxide of the element with atomic number 17?
(c) Which feature of the atomic structure accounts for the similarities in the chemical properties of the elements in group 7A of the periodic table?
(d) Name the element which has the highest ionization potential.
(e) How many electrons are present in the valency shell of the element with atomic number 18?

(f) What is the name given to the energy released when an atom in its isolated gaseous state accepts an electron to form an anion?
g) Fill in the blanks:
The atomic size ____________ as we move from left to right across the periods, because the________
increases but the______________remains the same.
Solution :
(a) (Al)2(SO4)3
(b) Covalent bonding
(c) Same number of valence electrons
(d) Helium
(e) 8
(f) Electron affinity
(g) The atomic size Decreases as we move from left to right across the periods, because the atomic number increases but the number of shells remains the same

Question : The electro negativities (according to pauling) of the elements in periodic table are as follows with the elements arranges in alphabetical order:

(a) Arrange the elements in the order in which they occur in the periodic table from left to right.
(The group 1 element first, followed by the group 2 element and so on, up to group 7)
(b) Choose the word or phrase from the brackets which correctly completes each of the following statements:-
(i) The element below sodium in the same group would be expected to have a _____ (lower/higher) electro-negativity than sodium and the element above chlorine would be expected to have a ______ (lower/ higher) ionization potential than chlorine.
(ii) On moving from left to right in a given period, the number of shells (remains the same/ increases/ decreases).
(iii) On moving down a group, the number of valence electrons (remains the same/ increases/ decreases).
Solution :
(a) Na, Mg, Al, Si, P, S, Cl
(b)
(i) The element in the same group below sodium should have a lower (lower/higher) electro-negativity than sodium, while the element above chlorine should have a greater (lower/higher) ionisation potential than chlorine.
(ii) remains the same
(iii) remains the same

Question : Parts (a) to (e) refer to changes In the properties of elements on moving from left to right across a period of the periodic table. For each property, choose the correct answer.

(a) The non-metallic character of the elements:
(i) decreases
(ii) increases,
(iii) remains the same,
(iv) depends on the period

Solution :

Increases

(b) The electronegativity:
(i) depends on the number of valence electrons,
(ii) remains the same,
(iii)decreases,
(iv)increases.

Solution :

Increases

(c) The ionization potential:
(i) goes up and down
(ii) decreases
(iii) increases
(iv) remains the same

Solution :

Increases

(d) The atomic size:
(i) decreases,
(ii) increases,
(iii) remains the same,
(iv) sometimes increases and sometimes decreases.

Solution :

Decreases

(e) The electron affinity of the elements in groups 1 to 7:
(i) goes up and then down.
(ii) decreases and then increases,
(iii) increases,
(iv) decreases.

Solution :

Increases

Question : The elements of one short period of the periodic table are given below in order from left to right:
Li Be B C O F Ne
(a) To which period do these elements belong?
(b) One element of this period is missing. Which is the missing element and where should it be placed?
(c) Which one of the elements in this period shows the property of catenation?
(d) Place the three elements fluorine, beryllium and nitrogen in the order of increasing electronegativity.
(e) Which one of the above elements belongs to the halogen series?
Solution :

(a) Period 2
(b) Nitrogen (N), between carbon and oxygen
(c) Carbon
(d) Be < N < F
(e) Fluorine

Question : A group of elements in the periodic table are given below (boron is the first member of the group and thallium is the last).
Boron, Aluminium, Gallium, Indium, Thallium.
Answer the following questions in relation to the above group of elements:
(a) Which element has the most metallic character?
(b) Which element would be expected to have the highest electronegativity?
(c) If the electronic configuration of aluminium is 2, 8, 3, how many electrons are there in the outer shell of thallium
(d) The atomic number of boron is 5. Write chemical formula of the compound formed when boron reacts with chlorine.
(e) Will the elements in the group to the right of this boron group be more metallic or less metallic in character? Justify your answer.
Solution :

(a) Since metallic character grows along the group, Thallium has the most metallic character.
(b) Because it is the smallest member of the group, boron has the highest electronegativity.
(c) 3. Because all members of a group have the same number of valence electrons.
(d) BCl3
(e) The elements in the group to the right of boron would be less metallic because it would be more difficult for them to lose electrons as their size and atomic number decreased.

Question : Select the correct answer from the choice A, B, C, D which are given. Write down only the letter corresponding to the correct answer.
With reference to the variation of properties in the periodic table, which of the following is generally true?
A. Atomic size increases from left to right across a period.
B. Ionization potential increases from left to right across a period.
C. Electron affinity increases going down a group.
D. electro-negativity increases going down a group.
Solution :

B. Ionization potential increases from left to right across a period.