Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$\text{Atomic mass} = (\text{fractional abundance}_1 \times \text{mass}_1) + (\text{fractional abundance}_2 \times \text{mass}_2)$$

Question 1

Which statement best describes Dalton’s Atomic Theory as it relates to chemical reactions?

Accepted Answer

Atoms combine in simple, whole-number ratios to form compounds, but are not created or destroyed in chemical reactions.

Question 2

In Rutherford’s gold foil experiment, what observation led to the conclusion that the atom has a small, dense nucleus?

Accepted Answer

A small number of alpha particles were deflected at large angles.

Question 3

Which of the following correctly describes the charge and mass of an electron?

Accepted Answer

Negative charge, mass much smaller than a proton

Question 4

A neutral atom of magnesium has 12 protons. If it loses two electrons during a chemical reaction, what is the resulting charge and number of electrons?

Accepted Answer

Charge: $$2^+$$, Electrons: 10

Question 5

Which element is represented by the chemical symbol 'K', and what is its origin?

Accepted Answer

Potassium, from the Latin 'kalium'

Question 6

Which group in the periodic table contains elements that are all gases at room temperature and are very unreactive?

Accepted Answer

Group VIIIA (Noble Gases)

Question 7

A chlorine atom has 17 protons and 18 neutrons. What is its mass number ($$A) $$and atomic number ($$Z$$)?

Accepted Answer

$$A = 35$$, $$Z = 17$$

Question 8

Which of the following pairs are isotopes?

Accepted Answer

$$^{39}\mathrm{K}$$	ext{ and }^{41}\mathrm{K}$

Question 9

Calculate the atomic mass of silver if it has two naturally occurring isotopes: $$^{107}\mathrm{Ag} ($$mass = $$106.90509$$ amu, abundance = $$51.84\%) $$and $$^{109}\mathrm{Ag} ($$mass = $$108.90476$$ amu, abundance = $$48.16\%).$$

Accepted Answer

Question 10

Which property is NOT characteristic of metals?

Accepted Answer

Brittleness

Question 11

A neutral atom of sulfur has 16 protons. If it gains two electrons, what is the charge and number of electrons in the resulting ion?

Accepted Answer

Charge: $$2^-$$, Electrons: 18

Question 12

Which of the following elements is a metalloid?

Accepted Answer

Silicon

Question 13

What is the main difference between cations and anions?

Accepted Answer

Cations are positively charged due to loss of electrons; anions are negatively charged due to gain of electrons.

Question 14

Which element is most likely to form a $$2^+$$ cation based on its position in the periodic table?

Accepted Answer

Calcium (Group IIA)

Question 15

A carbon isotope has 6 protons and 7 neutrons. What is its mass number ($$A) $$and chemical symbol?

Accepted Answer

$$A = 13$$, ^{13}\mathrm{C}$

Question 16

Which of the following best explains why noble gases are chemically inert?

Accepted Answer

They have a full valence electron shell, making it difficult to gain or lose electrons.

Question 17

Which equation correctly represents the formation of a lithium cation from a neutral lithium atom?

Accepted Answer

$$\mathrm{Li} \rightarrow \mathrm{Li}^+ + e^-$$

Question 18

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Atomic mass} = (	ext{fractional abundance}_1 	imes 	ext{mass}_1) + (	ext{fractional abundance}_2 	imes 	ext{mass}_2)$$

Question 19

Which of the following elements is most likely to form an anion with a $$-1$$ charge?

Accepted Answer

Fluorine

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