MCQs — Atomic Structure

Practice questions for Chemistry.

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Question 141

The regions around the nucleus where electrons are most likely to be found, arranged in increasing energy, are called:

A. Nuclear shells
B. Electron shells (energy levels)
C. Isotopic shells
D. Mass shells
Question 142

The first four electron shells, starting closest to the nucleus, are labelled:

A. K, L, M and N
B. A, B, C and D
C. S, P, D and F
D. 1, 2, 3 and 4 only, with no letters
Question 143

Each main electron shell can be divided into smaller energy divisions called:

A. Nuclei
B. Isotopes
C. Sub-shells
D. Ions
Question 144

The four main types of sub-shells are labelled:

A. K, L, M and N
B. A, B, C and D
C. 1, 2, 3 and 4
D. s, p, d and f
Question 145

According to this textbook, the maximum number of electrons that an s sub-shell can accommodate is:

A. 2
B. 6
C. 10
D. 14
Question 146

Using the sub-shell capacities given in the textbook (s = 2, p = 6, d = 10 electrons), what is the maximum number of electrons the M shell (n = 3, with sub-shells 3s, 3p and 3d) can hold?

A. 8
B. 18
C. 10
D. 32
Question 147

The principle that states electrons fill the lowest energy sub-shells first before occupying higher energy ones is called the:

A. Heisenberg Uncertainty Principle
B. Aufbau Principle
C. Pauli Exclusion Principle
D. Law of conservation of mass
Question 148

Why do electrons fill the K shell before the L shell in an atom?

A. Because the L shell does not exist in most atoms
B. Because electrons always fill shells in a completely random order
C. Because the K shell can hold more electrons than any other shell
D. Because the K shell has lower energy and is closer to the nucleus, so it fills first according to the Aufbau Principle
Question 149

The electronic configuration of sodium is written as 1s2 2s2 2p6 3s1, as shown in the textbook. How many electrons are present in its outermost sub-shell, 3s?

A. 1
B. 2
C. 6
D. 11
Question 150

An atom has 11 electrons. Following the Aufbau Principle (filling order 1s < 2s < 2p < 3s < 3p < 4s ...), what is its electronic configuration?

A. 1s2 2s2 2p6 3s1
B. 1s2 2s2 2p5 3s2
C. 1s2 2s2 2p7
D. 1s2 2s2 3s2 3p3

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