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 statement best summarizes Dalton’s atomic theory as it relates to the composition of compounds?

Accepted Answer

Atoms combine in simple, whole-number ratios to form compounds.

Question 2

Rutherford’s gold foil experiment led to which major revision of the atomic model?

Accepted Answer

Most of the atom’s mass and all its positive charge are concentrated in a small nucleus.

Question 3

Which of the following correctly describes the electrical charge and location of subatomic particles in an atom?

Accepted Answer

Neutrons are neutral and found in the nucleus.

Question 4

A neutral atom of potassium (K) has an atomic number of 19. How many electrons does it have?

Accepted Answer

$$19$$

Question 5

Which element is a metalloid and is commonly used in the electronics industry as a semiconductor?

Accepted Answer

Silicon

Question 6

Which group in the periodic table contains elements that are highly reactive nonmetals and includes chlorine and iodine?

Accepted Answer

Group 7A (Halogens)

Question 7

A magnesium ion has 10 electrons. What is its charge and symbol?

Accepted Answer

$$\mathrm{Mg}^{2+}$$

Question 8

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

Accepted Answer

They have a full outer shell of electrons.

Question 9

How many neutrons are in an isotope of boron with a mass number of 10?

Accepted Answer

$$5$$

Question 10

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 11

A sulfur ion has 18 electrons. What is its charge and symbol?

Accepted Answer

$$\mathrm{S}^{2-}$$

Question 12

Which of the following elements is a main group element and a metal?

Accepted Answer

Barium

Question 13

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 14

Which of the following best describes the trend in properties for elements in the same group of the periodic table?

Accepted Answer

They have similar chemical properties.

Question 15

A neutral atom of gold (Au) has an atomic number of 79 and a mass number of 197. How many neutrons does it have?

Accepted Answer

$$118$$

Question 16

Which of the following ions is formed when a fluorine atom gains one electron?

Accepted Answer

$$\mathrm{F}^{-}$$

Question 17

Which of the following best explains why sodium reacts violently with water while magnesium reacts less vigorously?

Accepted Answer

Sodium is an alkali metal and more reactive due to having only one valence electron.

Question 18

Which of the following is the correct isotope symbol for a neon atom with 10 protons and 12 neutrons?

Accepted Answer

$$^{22}\mathrm{Ne}$$

Question 19

A sample of chlorine contains 75.77% chlorine-35 (mass 34.97 amu) and 24.23% chlorine-37 (mass 36.97 amu). What is the average atomic mass of chlorine? (Round to two decimal places)

Accepted Answer

$$35.45\ \mathrm{amu}$$

Question 20

Which of the following best describes the difference between a cation and an anion?

Accepted Answer

A cation has more protons than electrons, while an anion has more electrons than protons.

Atoms and Elements: Structured Study Notes for Introductory Chemistry

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