$$\text{Atomic mass} = \sum_n (\text{fraction of isotope } n) \times (\text{mass of isotope } n)$$

$$2.00\ \text{mol} \times 6.022 \times 10$$^{23}$$\ \text{atoms/mol} = 1.204 \times 10$$^{24}$$\ \text{atoms}$$

Question 1

Which experiment provided evidence that atoms contain a small, dense, positively charged nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 2

According to the law of conservation of mass, what happens to the total mass during a chemical reaction?

Accepted Answer

It remains unchanged.

Question 3

A sample of water is decomposed into 16.0 g of oxygen and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen in water?

Accepted Answer

$$\frac{16.0\ \mathrm{g}\ O}{2.0\ \mathrm{g}\ H} = 8.0$$

Question 4

Which statement best describes isotopes?

Accepted Answer

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

Question 5

Which of the following is the correct formula for calculating the atomic mass of an element from its isotopes?

Accepted Answer

$$	ext{Atomic mass} = \sum_n (	ext{fraction of isotope } n) 	imes (	ext{mass of isotope } n)$$

Question 6

A neutral atom of sodium (Na) has an atomic number of 11 and a mass number of 23. How many neutrons does it contain?

Accepted Answer

12

Question 7

Which group of elements is characterized by being highly unreactive and having a full valence shell?

Accepted Answer

Noble gases (Group 8A)

Question 8

Which property is NOT characteristic of metals?

Accepted Answer

They are poor conductors of heat.

Question 9

How many atoms are present in 2.00 mol of carbon?

Accepted Answer

$$2.00\ 	ext{mol} 	imes 6.022 	imes 10$$^{23}$$\ 	ext{atoms/mol} = 1.204 	imes 10$$^{24}$$\ 	ext{atoms}$$

Question 10

Which of the following best explains why chlorine has an atomic mass of 35.45 amu?

Accepted Answer

It is the weighted average of the masses of its naturally occurring isotopes.

Question 11

A main-group element in Group 2A will most likely form which ion?

Accepted Answer

$$2^+$$ cation

Question 12

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

Accepted Answer

When elements are arranged in order of increasing atomic number, certain sets of properties recur periodically.

Question 13

Which scientist is credited with the discovery of the electron?

Accepted Answer

J.J. Thomson

Question 14

A sample contains 3.00 g of magnesium (Mg). How many moles of Mg are present? (Molar mass of Mg = 24.31 g/mol)

Accepted Answer

$$\frac{3.00\ \mathrm{g}}{24.31\ \mathrm{g/mol}} = 0.123\ \mathrm{mol}$$

Question 15

Which of the following is a property of nonmetals?

Accepted Answer

They tend to gain electrons during chemical reactions.

Question 16

Which element is a metalloid and often used in semiconductors?

Accepted Answer

Silicon

Question 17

A chlorine atom has 17 protons and 18 neutrons. What is its mass number?

Accepted Answer

35

Question 18

Which of the following best describes a cation?

Accepted Answer

An atom that has lost one or more electrons.

Question 19

Which of the following is the correct sequence for converting grams of an element to number of atoms?

Accepted Answer

$$	ext{grams} ightarrow 	ext{moles} ightarrow 	ext{number of atoms}$$

Atoms and Elements: Foundations of Modern Chemistry

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