Q: Calculate the molecular mass of carbon dioxide ($$\mathrm{CO_2$}) $$using the following atomic masses: C = $$12.01\ \mathrm{u}$$, O = $$16.00\ \mathrm{u}.$$

$$12.01\ \mathrm{u} + 2 \times 16.00\ \mathrm{u} = 44.01\ \mathrm{u}$$

Question 1

Which statement best describes the Law of Definite Composition as proposed by John Dalton?

Accepted Answer

A compound always contains the same elements in the same proportion by mass.

Question 2

According to Dalton’s Atomic Theory, which of the following is NOT true?

Accepted Answer

Atoms of the same element can have different numbers of protons.

Question 3

Which experiment led to the discovery of the electron?

Accepted Answer

Thomson’s cathode ray tube experiment

Question 4

What is the charge and relative mass of a proton?

Accepted Answer

Charge: $$+1$$, Relative mass: $$1$$

Question 5

Which scientist is credited with discovering the neutron?

Accepted Answer

James Chadwick

Question 6

An atom of oxygen has 8 protons and 10 neutrons. What is its mass number?

Accepted Answer

$$A = 8 + 10 = 18$$

Question 7

Which of the following best explains why atoms are electrically neutral?

Accepted Answer

The number of protons equals the number of electrons.

Question 8

What is the nuclear symbol for an isotope of uranium with 92 protons and 143 neutrons?

Accepted Answer

$$\mathrm{^{235}_{92}U}$$

Question 9

Which statement about ions is correct?

Accepted Answer

A cation is formed when an atom loses electrons.

Question 10

A sample of carbon contains 98.9% $$^{12}C$$, 1.1% $$^{13}C$$, and less than 0.1% $$^{14}C. $$What is the average atomic mass of carbon?

Accepted Answer

$$12.011\ \mathrm{u}$$

Question 11

Which model of the atom first proposed the existence of a dense, positively charged nucleus?

Accepted Answer

Rutherford’s nuclear model

Question 12

If a sodium atom ($$Z=11) $$loses one electron, what is the resulting ion’s charge?

Accepted Answer

$$+1$$

Question 13

Which of the following best describes isotopes?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 14

Calculate the molecular mass of carbon dioxide ($$\mathrm{CO_2$}) $$using the following atomic masses: C = $$12.01\ \mathrm{u}$$, O = $$16.00\ \mathrm{u}.$$

Accepted Answer

$$12.01\ \mathrm{u} + 2 	imes 16.00\ \mathrm{u} = 44.01\ \mathrm{u}$$

Question 15

Which of the following is a consequence of the Law of Conservation of Mass?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 16

Which subatomic particle has a relative mass close to zero and a charge of $$-1$$?

Accepted Answer

Electron

Question 17

A magnesium atom has 12 protons, 12 neutrons, and 12 electrons. What is its atomic number and mass number?

Accepted Answer

Atomic number: $$12$$, Mass number: $$24$$

Question 18

Which statement about the space occupied by electrons in the atom is correct according to the nuclear model?

Accepted Answer

Electrons occupy a large volume of space around the nucleus.

Question 19

Which of the following best explains why the atomic mass listed on the periodic table is not a whole number?

Accepted Answer

It is a weighted average of all naturally occurring isotopes of the element.

Atoms and Elements: Foundations of Atomic Theory

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