Lesson: Periodic Classification of Elements

# Question: 1

Which of the following statements is not a correct statement about the trends when going from left to right across the periods of the Periodic Table?

(a) The elements become less metallic in nature.

(b) The number of valence electrons increases.

(c) The atoms lose their electrons more easily.

(d) The oxides become more acidic.

(c)

# Question:2

Element X forms a chloride with the formula $XC{l}_{2}$, which is a solid with a high

melting point. X would most likely be in the same group of the Periodic Table as

(a) Na

(b) Mg

(c) AI

(d) Si

(b)

# Question:3

Which element has:

(a) two shells, both of which are completely filled with electrons?

(b) the electronic configuration 2, 8, 2?

(c) a total of three shells, with four electrons in its valence shell?

(d) a total of two shells, with three electrons in its valence shell?

(e) twice as many electrons in its second shell as in its first shell?

(a) Neon

(b) Magnesium

(c) Silicon

(d) Boron

(e) Carbon

# Question:4

(a) What property do all elements in the same column of the Periodic Table as boron have in common?

(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?

## Solution:

(a) Valency equal to 3.

(b) Valency equal to 1.

# Question:5

An atom has electronic configuration 2, 8, 7.

(a) What is the atomic number of this element?

(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)

N (7), F (9), P (15), Ar (18)

## Solution:

(a) 17.

(b) Fluorine (F) with the configuration as 2, 7

# Question:6

The position of three elements A, B and C in the Periodic Table are shown below

 Group 16 Group 17 - - - A - - B C

(a) State whether A is a metal or non-metal.

(b) State whether C is more reactive or less reactive than A.

(c) Will C be larger or smaller in size than B?

(d) Which type of ion, cation or anion, will be formed by element A?

## Solution:

(a)   A is a non-metal.

(b)   C is less reactive than A, as reactivity decreases down the group in halogens.

(c)   C will be smaller in size than B as moving across a period, the nuclear charge increases. Therefore, electrons come closer to the nucleus.

(d)   A will form an anion as it accepts an electron to complete its octet.

# Question:7

Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to

group 15 of the Periodic Table. Write the electronic configuration of these two

elements. Which of these will be more electronegative? Why?

## Solution:

Nitrogen (7): 2, 5

Phosphorus (15): 2, 8, 5

Since, electronegativity decreases with moving from top to bottom in a group, nitrogen will be more electronegative.

# Question:8

How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

## Solution:

In the Modern Periodic Table, atoms with similar electronic configurations are placed in the same column. In a group, the number of valence electrons remains the same. Elements across a period show an increase in the number of valence electrons.

# Question:9

In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?

## Solution:

Both calcium and the elements with atomic number 12 and 38 have same number of valence electrons, i.e. 2. Hence both these elements have the same properties.

# Question: 10

Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table

and the Modern Periodic Table.

## Solution:

 Mendeleev's Periodic Table Modern Periodic Table Elements are arranged in the increasing order of their atomic masses. Elements are arranged in the increasing order of their atomic numbers. There are 8 Groups. There are 18 Groups. Groups are subdivided into sub-groups. Groups are not subdivided into sub-groups. Groups for noble gases were not present. A separate group is meant for noble gases. Position of isotopes could not be explained by Mendeleev’s periodic table. Position of isotopes is well explained.