Q: A sample of chlorine contains 75.77% $$^{35}\mathrm{Cl} ($$mass = 35.0 amu) and 24.23% $$^{37}\mathrm{Cl} ($$mass = 37.0 amu). What is the atomic mass of chlorine?

$$0.7577 \times 35.0 + 0.2423 \times 37.0 = 35.5$$ amu

Q: How many electrons can be held in the $$n=3$$ principal energy level?

$$2n^2 = 2$$ \times $$3^2 = 18$

Question 1

Which statement best describes the difference between isotopes of the same element?

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 2

A neutral atom of phosphorus has an atomic number of 15 and a mass number of 31. How many neutrons does it contain?

Accepted Answer

$$31 - 15 = 16$$ neutrons

Question 3

Which experiment provided evidence for the existence of a small, dense, positively charged nucleus in the atom?

Accepted Answer

Rutherford's gold foil experiment

Question 4

Which of the following ions is isoelectronic with neon ($$\mathrm{Ne}$$)?

Accepted Answer

$$\mathrm{Na^+}$$

Question 5

What is the electron configuration for a neutral atom of magnesium ($$Z=12$$)?

Accepted Answer

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

Question 6

Which of the following best explains why atomic size increases as you move down a group in the periodic table?

Accepted Answer

The valence electrons are in higher principal energy levels, farther from the nucleus.

Question 7

Which of the following elements is most likely to form a $$2^+$$ cation to achieve a noble gas configuration?

Accepted Answer

Magnesium ($$\mathrm{Mg})$$

Question 8

A sample of chlorine contains 75.77% $$^{35}\mathrm{Cl} ($$mass = 35.0 amu) and 24.23% $$^{37}\mathrm{Cl} ($$mass = 37.0 amu). What is the atomic mass of chlorine?

Accepted Answer

$$0.7577 	imes 35.0 + 0.2423 	imes 37.0 = 35.5$$ amu

Question 9

Which of the following statements about the Bohr model of the atom is correct?

Accepted Answer

Electrons occupy quantized energy levels and can move between them by absorbing or emitting energy.

Question 10

Which of the following best describes the trend in ionization energy across a period from left to right?

Accepted Answer

Ionization energy increases because the outer electrons are held more tightly by the increasing nuclear charge.

Question 11

Which of the following electron configurations represents a noble gas?

Accepted Answer

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

Question 12

Which of the following ions is the smallest in size?

Accepted Answer

$$\mathrm{Fe$$^{3+}$$}$$

Question 13

Which principle states that electrons fill the lowest energy orbitals available first?

Accepted Answer

Aufbau Principle

Question 14

How many electrons can be held in the $$n=3$$ principal energy level?

Accepted Answer

$$2n^2 = 2$$ 	imes $$3^2 = 18$

Question 15

Which of the following best explains why nonmetals tend to form anions?

Accepted Answer

Nonmetals gain electrons to achieve a stable noble gas electron configuration.

Question 16

Which of the following is the correct shorthand electron configuration for potassium ($$Z=19$$)?

Accepted Answer

$$[Ar]4s^1$

Question 17

Which of the following statements about the periodic law is correct?

Accepted Answer

The physical and chemical properties of the elements are periodic functions of their atomic numbers.

Question 18

Which of the following best describes Hund's Rule?

Accepted Answer

Each orbital in a subshell is half-filled before any becomes completely filled.

Question 19

Which of the following elements is a metalloid?

Accepted Answer

Silicon ($$\mathrm{Si})$$

Question 20

Which of the following best explains why noble gases are generally unreactive?

Accepted Answer

They have a full complement of valence electrons in their outermost s and p sublevels.

Chapter 2: The Structure of the Atom and the Periodic Table – Study Notes

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