$$A_r = (0.75 \times 35) + (0.25 \times 37) = 35.5$$

Question 1

Which of the following statements best describes an isotope?

Accepted Answer

Atoms of the same element with the same number of protons but different numbers of neutrons.

Question 2

A chlorine molecule can have a mass of 70, 72, or 74. Which combination of isotopes corresponds to a mass of 72?

Accepted Answer

$$^{35}\mathrm{Cl}$$ and $$^{37}\mathrm{Cl}$$

Question 3

Which subatomic particle is responsible for the chemical properties of an element?

Accepted Answer

Electron

Question 4

What is the electronic configuration of nitrogen (N) according to Hund’s rule?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ 2p_$$x^1$$\ 2p_$$y^1$$\ 2p_$$z^1$$

Question 5

Which factor does NOT affect the first ionization energy of an element?

Accepted Answer

Number of isotopes

Question 6

Why is the first ionization energy of oxygen lower than that of nitrogen?

Accepted Answer

Because of increased electron-electron repulsion due to paired electrons in the 2p orbital of oxygen.

Question 7

Which of the following best explains the trend in atomic radius across a period?

Accepted Answer

Atomic radius decreases due to increasing nuclear charge pulling electrons closer.

Question 8

A sample contains 75% $$^{35}\mathrm{Cl}$$ and 25% $$^{37}\mathrm{Cl}. $$What is the relative atomic mass ($$A_r) of $$chlorine?

Accepted Answer

$$A_r = (0.75 	imes 35) + (0.25 	imes 37) = 35.5$$

Question 9

Which step in a mass spectrometer is responsible for separating ions based on their mass-to-charge ratio ($$m/z$$)?

Accepted Answer

Deflection by a magnetic field

Question 10

Which of the following elements has the highest first ionization energy?

Accepted Answer

Neon (Ne)

Question 11

What is the maximum number of electrons that can be held in the third quantum shell?

Accepted Answer

18

Question 12

Which of the following best describes the shape of a p-orbital?

Accepted Answer

Dumbbell-shaped

Question 13

Why does the first ionization energy decrease as you move down a group in the periodic table?

Accepted Answer

Because atomic radius and shielding increase, reducing the attraction between the nucleus and outer electrons.

Question 14

Which of the following is the correct electronic configuration for potassium (K, atomic number 19)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^6$$\ $$4s^1$$

Question 15

Which principle states that two electrons cannot occupy the same orbital unless they have opposite spins?

Accepted Answer

Pauli Exclusion Principle

Question 16

Which block of the periodic table contains elements whose highest energy electrons are in a d-orbital?

Accepted Answer

d-block

Question 17

A mass spectrum of a diatomic molecule shows three peaks at $$m/z$$ values of 70, 72, and 74. What does the peak at 74 represent?

Accepted Answer

A molecule containing two $$^{37}\mathrm{Cl}$$ atoms

Question 18

Which of the following best explains why the melting point of diamond (carbon) is much higher than that of oxygen?

Accepted Answer

Diamond has a giant lattice structure, while oxygen is a simple molecular structure.

Question 19

Which of the following is the correct order of filling for the first four electron sub-shells according to the Aufbau principle?

Accepted Answer

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s$$

Atomic Structure and Periodic Table: Study Notes for Introductory Chemistry

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