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

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

Question 1

Which of the following statements is NOT part of Dalton’s atomic theory as presented in this chapter?

Accepted Answer

Matter is neither created nor destroyed in chemical reactions.

Question 2

A neutral atom of magnesium-24 ($$^{24}\mathrm{Mg}) $$has how many protons, neutrons, and electrons?

Accepted Answer

12 protons, 12 neutrons, 12 electrons

Question 3

Which subatomic particle is responsible for the chemical identity of an element?

Accepted Answer

Proton

Question 4

A fluorine ion has 9 protons and 10 electrons. What is its symbol and charge?

Accepted Answer

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

Question 5

Which element is a metalloid and is commonly used in semiconductors?

Accepted Answer

Silicon

Question 6

How many electrons are present in a $$\mathrm{P}^{3-}$$ ion?

Accepted Answer

18

Question 7

Which of the following best describes a halogen?

Accepted Answer

A nonmetal in Group 7A that tends to gain one electron to form a $$-1$$ ion

Question 8

A sample of element X contains two isotopes: X-10 (mass $$10.0$$ amu, $$20\%$$ abundance) and X-11 (mass $$11.0$$ amu, $$80\%$$ abundance). What is the average atomic mass of X?

Accepted Answer

$$10.8$$ amu

Question 9

Which of the following ions has the same number of electrons as a neutral argon atom ($$Z=18$$)?

Accepted Answer

$$\mathrm{Cl}^{-}$$

Question 10

A certain isotope of iron is represented as $$^{56}\mathrm{Fe}^{3+}. $$How many protons, neutrons, and electrons does it have?

Accepted Answer

26 protons, 30 neutrons, 23 electrons

Question 11

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 12

Which element is expected to react with water most similarly to potassium?

Accepted Answer

Sodium

Question 13

A radioactive isotope is used in medical imaging because it emits radiation that can be detected by scanners. Which property makes this possible?

Accepted Answer

Its nucleus is unstable and emits energetic subatomic particles.

Question 14

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons and has a positive charge

Question 15

The atomic mass of chlorine is approximately $$35.45$$ amu. If chlorine consists of $$75.77\%$$ $$^{35}\mathrm{Cl} ($$mass $$34.97$$ amu) and $$24.23\%$$ $$^{37}\mathrm{Cl} ($$mass $$36.97$$ amu), which isotope is more abundant and why?

Accepted Answer

$$^{35}\mathrm{Cl}$$, because the average atomic mass is closer to $$34.97$$ amu

Question 16

Which of the following elements is a noble gas?

Accepted Answer

Argon

Question 17

A sample of gallium contains $$60.11\%$$ $$^{69}\mathrm{Ga} ($$mass $$68.9256$$ amu) and $$39.89\%$$ $$^{71}\mathrm{Ga} ($$mass $$70.9247$$ amu). What is the average atomic mass of gallium? (Round to two decimal places.)

Accepted Answer

$$69.72$$ amu

Question 18

Which of the following best explains why elements in the same group of the periodic table have similar chemical properties?

Accepted Answer

They have the same number of valence electrons.

Question 19

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

Accepted Answer

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

Question 20

A neutral atom of element Q has 20 protons and 20 neutrons. If it loses two electrons, what is its resulting ion symbol and charge?

Accepted Answer

$$^{40}\mathrm{Q}^{2+}$$

Atoms and Elements: Study Guide for Introduction to Chemistry (CHM1025, Chapter 4)

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