Structure of the atom Worksheet-4

Structure of the atom Worksheet-4

11. Which of the following elements contains only two electrons in the outermost shell?

A. Helium                                       B. Beryllium

C. Magnesium                               D. All the above

12. Mass of neutron is :

A. equal to that of electron

B. equal to that of proton

C. less than that of proton

D. slightly more than that of proton

13. Which is not true about neutron?

A. It is a neutral particle.

B. It is present in the nucleus of atom

C. It is highly unstable in nature

D. It contributes to the mass of the atom.

14. Which is the correct electronic configuration of the element Al?

A. 2,8                  B. 2,8,2              C. 2,8,3              D. 2,8,1

15. The mass of an electron is :

A. 1.6 × 10^–30 Kg                           B. 6.1 × 10^–27 Kg

C. 9.1 × 10^–31 Kg                           D. 9.1 × 10^–27 Kg

16. Positive ion is formed from the neutral atom by the loss of:

A. protons                                      B. neutrons

C. alpha particles                         D. electrons

17. Maximum number of electrons which can be filled in the third shell of an atom is:

A. 8                     B. 18                    C. 10                   D. 32

18. Which of the following elements have same number of protons, electrons and neutrons?

A. Al                    B. Mg                  C. P                     D. CI

19. Which of the following does not have 18 electrons?

A. K⁺                                                B. Ca²⁺

C. Cl^–                                               D. all have 18 electrons

20. Number of valence electrons in an element ₇X¹⁴ is :

A. 5                      B. 1                      C. 7                      D. 3

21. Anion is formed when an atom :

A. loses electrons

B. loses protons

C. loses protons and electrons

D. Gains electrons

22. Which of the following elements shows valency of 2 in its compounds:

A. Nitrogen (Z = 7)                      B. Fluorine (Z = 9)

C. Magnesium (Z = 12)               D. Silicon (Z = 14)

Answer Key:

11. D

Explanation:

He atomic number –2 configuration –2(K)

He atomic number –4 configuration –2(K), 2(L)

He atomic number –12 configuration –2(K), 8(L), 2(M)

12. D

13. C

14. C

Explanation: Atomic number of Al is 13 - 2,8,3

15. C

16. D

Explanation: Mg ® Mg²⁺ + 2e^– Cation is formed by loss of electrons.

17. B

Explanation: Maximum number of electrons which can be filled in a shell = 2n², n = 3, 2 × 3² = 18

18. B

Explanation: ₁₂Mg²⁴ It has equal number of protons, electrons and neutrons.

₁₃Al²⁷ p = 13, n = 14, e = 13

₁₅P³¹ p = 15, n = 16, e = 15

₁₇Cl³⁵ p = 17, n = 18, e = 17

19. D

20. A

Explanation: ₇X¹⁴ 2(K), 8(L), 4(M) 4 valence electrons are present in the element.

21. D

Explanation: Cl + e^– → Cl^– Anion is formed when an atom gains electrons.

22. C

Explanation: The number of valence electrons in Mg is 2. Hence it shows valency 2 in its compounds.

Mg electronic distribution : 2(K), 8(L), 2(M)

N electronic distribution –2(K), 5(L) Valency = 3

E electronic distribution –2(K), 7(L) Valency = 1

Si electronic distribution –2(K), 8(L), 4(M) Valency = 4