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

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

Question 1

Which of the following statements best describes a chemical compound?

Accepted Answer

A substance composed of two or more different elements combined in a fixed ratio.

Question 2

Which group on the periodic table contains elements that are shiny, ductile, and good conductors of heat and electricity?

Accepted Answer

Metals (left side of the periodic table)

Question 3

Which of the following is the correct ground-state electron configuration for carbon (atomic number 6)?

Accepted Answer

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

Question 4

A sample of magnesium contains 78.70% $$^{24}Mg ($$mass = 23.99 amu), 10.13% $$^{25}Mg ($$mass = 24.99 amu), and 11.17% $$^{26}Mg ($$mass = 25.98 amu). What is the average atomic mass of magnesium? (Round to two decimal places)

Accepted Answer

$$24.31\ 	ext{amu}$$

Question 5

Which of the following statements about isotopes is TRUE?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 6

Which of the following best describes the location and charge of a neutron?

Accepted Answer

Located in the nucleus; no charge

Question 7

Which element is a member of Group 1A (alkali metals) and reacts vigorously with water?

Accepted Answer

Sodium (Na)

Question 8

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

Accepted Answer

Groups are vertical columns and periods are horizontal rows.

Question 9

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

Accepted Answer

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

Question 10

Which of the following best explains why metals are good conductors of electricity?

Accepted Answer

They have loosely held valence electrons that can move freely.

Question 11

Which of the following elements is a halogen?

Accepted Answer

Bromine (Br)

Question 12

Which of the following statements about electron energy levels is correct?

Accepted Answer

The number of sublevels in an energy level is equal to the principal quantum number $$n.$$

Question 13

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

Accepted Answer

15 protons, 16 neutrons, 15 electrons

Question 14

Which of the following best describes a metalloid?

Accepted Answer

An element that exhibits properties of both metals and nonmetals.

Question 15

Which of the following is the correct order of sublevels in an energy level, according to increasing energy?

Accepted Answer

$$s \u003c p \u003c d \u003c f$$

Question 16

Which of the following statements about atomic spectra is TRUE?

Accepted Answer

Atomic spectra are produced when electrons move from higher to lower energy levels and emit energy as light.

Question 17

Which of the following is a correct statement about the mass number of an atom?

Accepted Answer

It represents the total number of protons and neutrons in the nucleus.

Question 18

Which of the following elements is a noble gas?

Accepted Answer

Argon (Ar)

Question 19

A hospital uses a radioactive isotope with a half-life of 6 hours for diagnostic imaging. If a patient is injected with 80 mg of the isotope, how much remains after 18 hours?

Accepted Answer

$$10\ 	ext{mg}$$

Question 20

Which of the following best explains why nonmetals are often poor conductors of electricity?

Accepted Answer

They have tightly held electrons that do not move easily.

Fundamentals of Chemistry: Elements, Atomic Structure, and Electron Energy Levels

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