Q: Which equation correctly calculates the average atomic mass of an element with two isotopes: $$^{6}\mathrm{Li} (7.5$$% abundance, mass = 6.015 u) and $$^{7}\mathrm{Li} (92.5$$% abundance, mass = 7.016 u)?

$$\text{Average atomic mass} = (0.075 \times 6.015) + (0.925 \times 7.016)$$

Question 1

Which of the following statements best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 2

A neutral atom of sodium has 11 protons. If it loses one electron, what is the resulting charge?

Accepted Answer

$$+1$$

Question 3

Which equation correctly calculates the average atomic mass of an element with two isotopes: $$^{6}\mathrm{Li} (7.5$$% abundance, mass = 6.015 u) and $$^{7}\mathrm{Li} (92.5$$% abundance, mass = 7.016 u)?

Accepted Answer

$$	ext{Average atomic mass} = (0.075 	imes 6.015) + (0.925 	imes 7.016)$$

Question 4

Which force is responsible for holding protons and neutrons together in the nucleus?

Accepted Answer

Strong nuclear force

Question 5

What is the charge of an oxygen ion with 8 protons and 10 electrons?

Accepted Answer

$$-2$$

Question 6

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

Accepted Answer

They have equal numbers of protons and electrons.

Question 7

If a carbon atom has 6 protons, 6 neutrons, and 6 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number = 6, Mass number = 12

Question 8

Which statement about the electron cloud model is correct?

Accepted Answer

Electrons are found in regions of high probability called orbitals.

Question 9

A sample contains 90% $$^{12}\mathrm{C} ($$mass = 12.000 u) and 10% $$^{13}\mathrm{C} ($$mass = 13.003 u). What is the average atomic mass?

Accepted Answer

$$12.100\ \mathrm{u}$$

Question 10

Which of the following is a correct description of an ion?

Accepted Answer

An atom that has gained or lost electrons.

Question 11

Which of the following best describes the role of electrons in chemical bonding?

Accepted Answer

Electrons are shared or transferred between atoms to form bonds.

Question 12

What is the main reason why the nucleus of an atom does not fly apart due to repulsion between protons?

Accepted Answer

The strong nuclear force overcomes the repulsive electromagnetic force.

Question 13

Which of the following is true about the charge of a neutron?

Accepted Answer

It is neutral.

Question 14

A sodium ion ($$\mathrm{Na}^+) $$has 11 protons and 10 electrons. What is its net charge?

Accepted Answer

$$+1$$

Question 15

Which of the following best explains why isotopes of the same element have nearly identical chemical properties?

Accepted Answer

They have the same number of protons and electrons.

Question 16

Which process describes the spontaneous emission of particles or energy from an unstable nucleus?

Accepted Answer

Radioactivity

Question 17

If an atom has 15 protons, 16 neutrons, and 18 electrons, what is its charge?

Accepted Answer

$$-3$$

Question 18

Which of the following is NOT a property of the electron cloud?

Accepted Answer

It is a fixed path around the nucleus.

Question 19

Which of the following best describes the relationship between atomic number and the identity of an element?

Accepted Answer

The atomic number determines the number of protons and thus the element.

Question 20

Which of the following is a real-world application of ions?

Accepted Answer

Ions are used in the conduction of electricity in saltwater.

Class 3, Ch. 5.1: Structure of the Atom

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