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

$$\text{Average mass} = (\text{fraction}_1 \times \text{mass}_1) + (\text{fraction}_2 \times \text{mass}_2)$$

Question 1

Which of the following statements best explains why elements in the same group of the periodic table tend to form ions with the same charge?

Accepted Answer

They have the same number of valence electrons.

Question 2

A neutral atom of magnesium ($$Z = 12) $$has how many electrons, and what is the charge of the ion it most commonly forms?

Accepted Answer

12 electrons; forms a $$\mathrm{Mg}^{2+}$$ ion

Question 3

Which of the following ions is a polyatomic anion?

Accepted Answer

$$\mathrm{SO}_4$$^{2-}$$

Question 4

An atom has 17 protons and 18 neutrons. What is its mass number, and what is the correct isotope symbol?

Accepted Answer

Mass number = 35; $$^{35}_{17}\mathrm{Cl}$$

Question 5

Which of the following best describes isotopes of an element?

Accepted Answer

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

Question 6

A sample of chlorine contains 75.77% $$^{35}\mathrm{Cl} ($$mass = 35 amu) and 24.23% $$^{37}\mathrm{Cl} ($$mass = 37 amu). What is the average atomic mass of chlorine?

Accepted Answer

$$35.45$$ amu

Question 7

Which of the following statements about electrons in atoms is correct?

Accepted Answer

Electrons are located in specific energy levels or shells.

Question 8

When an atom emits light in its emission spectrum, what is happening at the atomic level?

Accepted Answer

Electrons are moving from a higher energy level to a lower energy level.

Question 9

Which of the following ions is most likely to be formed by an atom of sulfur ($$Z = 16$$)?

Accepted Answer

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

Question 10

A neutral atom of tin ($$Z = 50) $$has 69 neutrons. What is the isotope symbol for this atom?

Accepted Answer

$$^{119}_{50}\mathrm{Sn}$$

Question 11

Which of the following best explains why the emission spectrum of hydrogen consists of specific lines rather than a continuous spectrum?

Accepted Answer

Electrons can only occupy specific energy levels, so only certain energy transitions are possible.

Question 12

Which of the following ions is a cation?

Accepted Answer

$$\mathrm{NH}_4^+$$

Question 13

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

Accepted Answer

$$3-$$

Question 14

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

Accepted Answer

$$	ext{Average mass} = (	ext{fraction}_1 	imes 	ext{mass}_1) + (	ext{fraction}_2 	imes 	ext{mass}_2)$$

Question 15

Which of the following best describes a valence electron?

Accepted Answer

An electron in the outermost occupied shell of an atom.

Question 16

A hospital technician is analyzing a sample of titanium that contains 7.28% $$^{47}\mathrm{Ti} ($$mass = 47 amu), 73.94% $$^{48}\mathrm{Ti} ($$mass = 48 amu), 5.51% $$^{49}\mathrm{Ti} ($$mass = 49 amu), and 5.34% $$^{50}\mathrm{Ti} ($$mass = 50 amu). What is the approximate average atomic mass of this titanium sample?

Accepted Answer

$$48.93$$ amu

Question 17

Which of the following statements about core electrons is correct?

Accepted Answer

Core electrons are found in the innermost shells and do not participate in chemical bonding.

Question 18

Which of the following best explains why the number of protons in an atom determines its identity?

Accepted Answer

The number of protons defines the atomic number, which is unique for each element.

Question 19

Which of the following is a correct statement about the relationship between electrons and protons in a neutral atom?

Accepted Answer

The number of electrons equals the number of protons.

Periodic Table, Ions, Isotopes, and Atomic Structure: CHM 119 Lecture 3 Study Notes

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