Classification of Elements - The Periodic Table — Practice

Question 1

Number of elements present in period 2 of the long form of the periodic table

Accepted Answer

8

Question 2

Nitrogen (Z = 7) is in group VA of the periodic table. Which of the following is the atomic number of the next element in the same group?

Accepted Answer

15

Question 3

The electron configuration of an atom is 2, 8, 7. To which of the following elements would it be chemically similar?

Accepted Answer

fluorine (Z = 9)

Question 4

Which of the following is the most active metal?

Accepted Answer

rubidium

Question 5

Identify the element with the larger atomic radius in each pair: (i) Mg, Ca (ii) Li, Cs (iii) N, P (iv) B, Al.

Accepted Answer

Ca, Cs, P and Al.

Question 6

Identify the element with the lower ionization energy in each pair: (i) Mg, Na (ii) Li, O (iii) Br, F (iv) K, Br.

Accepted Answer

Na, Li, Br and K.

Question 7

Given the electronic configurations A = 1s2 2s2, B = 1s2 2s2 2p6 3s2, C = 1s2 2s2 2p6 3s2 3p3, D = 1s2 2s2 2p6 - which are in the same period, which in the same group, which is a noble gas, and to which group and period does C belong?

Accepted Answer

A and D are in period 2; B and C are in period 3. A and B are in the same group, group 2. D is the noble gas neon. C belongs to group 15 (VA) and period 3.

Question 8

On the basis of atomic number, predict the block to which the elements with atomic numbers 9, 37, 46 and 64 belong.

Accepted Answer

9 is p-block, 37 is s-block, 46 is d-block and 64 is f-block.

Question 9

Using the periodic table, predict the formula of the compound formed between an element X of group 13 and an element Y of group 16.

Accepted Answer

X2Y3.

Question 10

An element has atomic number 19. Where would you expect this element to be in the periodic table, and why?

Accepted Answer

In group 1 (IA), period 4 - it is potassium, an alkali metal.

Question 11

The densities of calcium and barium are 1.55 and 3.51 g per cm cubed. Using Dobereiner's law of triads, give the approximate density of strontium.

Accepted Answer

About 2.53 g per cm cubed.

Question 12

Write down the characteristics of the element having atomic number 17 - configuration, period, group, family, valence electrons, valency, and whether it is a metal or a non-metal.

Accepted Answer

Configuration 1s2 2s2 2p6 3s2 3p5; period 3; group 17 (VIIA); halogen family; 7 valence electrons; valency 1; non-metal.

Question 13

The second period element fluorine has a smaller electron gain enthalpy than the third period element chlorine of the same group. Why?

Accepted Answer

Because fluorine's 2p sub-shell is so small that the incoming electron meets strong repulsion from the electrons already crowded there, which offsets part of the energy released. Chlorine's 3p sub-shell is larger, the repulsion is less, and more energy is liberated - Cl at -349 against F at -328 kJ per mol.

Question 14

Why is the second ionization energy of an element always higher than its first ionization energy?

Accepted Answer

Because the second electron is being removed from a positive ion, not a neutral atom. The ion has one electron fewer than it has protons, so every remaining electron is held more tightly, and more energy is needed.

Question 15

In period 2, element X is to the right of element Y. Which of the two has: (i) low nuclear charge (ii) low atomic size (iii) high ionization energy (iv) high electronegativity (v) more metallic character?

Accepted Answer

Y has low nuclear charge, high metallic character; X has low atomic size, high ionization energy and high electronegativity.

Question 16

Complete the period table: for periods 1 to 7, state the sub-shells filled, the maximum number of electrons and the total number of elements in the period.

Accepted Answer

Period 1: 1s, 2 electrons, 2 elements. Period 2: 2s 2p, 8, 8. Period 3: 3s 3p, 8, 8. Period 4: 4s 3d 4p, 18, 18. Period 5: 5s 4d 5p, 18, 18. Period 6: 6s 4f 5d 6p, 32, 32. Period 7: 7s 5f 6d 7p, 32, incomplete.

Practice — Classification of Elements - The Periodic Table

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