Q: The atomic mass of gallium is calculated using its two isotopes: Ga-69 (mass = $$68.9256$$ amu, abundance = $$60.11\%) $$and Ga-71 (mass = $$70.9247$$ amu, abundance = $$39.89\%). $$What is the atomic mass of gallium?

$$68.9256 \times 0.6011 + 70.9247 \times 0.3989 = 69.72$$ amu

Q: A sample contains $$2.0$$ grams of carbon-12. How many atomic mass units (amu) does this sample contain? ($$1$$ amu $$= 1.66 \times 10$$^{-24}$$ g)

$$2.0 \text{ g} \div 1.66 \times 10$$^{-24}$$ \text{ g/amu} = 1.2 \times 10$$^{24}$$ amu

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

$$\text{Atomic mass} = (\text{fraction}_1 \times \text{mass}_1) + (\text{fraction}_2 \times \text{mass}_2) + (\text{fraction}_3 \times \text{mass}_3)$$

Question 1

Which of the following statements best explains the main conclusion from Rutherford’s gold foil experiment?

Accepted Answer

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

Question 2

A neutral atom of sodium (Na) has an atomic number of 11 and a mass number of 23. How many neutrons does it contain?

Accepted Answer

$$23 - 11 = 12$$ neutrons

Question 3

Which property is NOT typical of metals?

Accepted Answer

Brittle when solid

Question 4

What is the charge on an ion formed when a chlorine atom gains one electron?

Accepted Answer

$$1-$$

Question 5

Which of the following elements is a metalloid?

Accepted Answer

Silicon (Si)

Question 6

The atomic mass of gallium is calculated using its two isotopes: Ga-69 (mass = $$68.9256$$ amu, abundance = $$60.11\%) $$and Ga-71 (mass = $$70.9247$$ amu, abundance = $$39.89\%). $$What is the atomic mass of gallium?

Accepted Answer

$$68.9256 	imes 0.6011 + 70.9247 	imes 0.3989 = 69.72$$ amu

Question 7

Which of the following is the correct symbol for the element with atomic number 19?

Accepted Answer

K

Question 8

A neutral atom of aluminum (Al) loses three electrons. What is the resulting ion’s charge and symbol?

Accepted Answer

$$\mathrm{Al}^{3+}$$

Question 9

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 10

Which group in the periodic table contains elements that are all gases at room temperature and are chemically inert?

Accepted Answer

Group 8A (Noble gases)

Question 11

A sample contains $$2.0$$ grams of carbon-12. How many atomic mass units (amu) does this sample contain? ($$1$$ amu $$= 1.66 	imes 10$$^{-24}$$ g)

Accepted Answer

$$2.0 	ext{ g} \div 1.66 	imes 10$$^{-24}$$ 	ext{ g/amu} = 1.2 	imes 10$$^{24}$$ amu

Question 12

Which of the following best describes why sodium (Na) forms a $$1+$$ ion and chlorine (Cl) forms a $$1-$$ ion?

Accepted Answer

Sodium loses one electron to achieve a stable electron configuration, while chlorine gains one electron.

Question 13

Which of the following elements is most likely to be a good conductor of electricity and have a high melting point?

Accepted Answer

Copper (Cu)

Question 14

If an atom has 17 protons, 18 neutrons, and 17 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number $$= 17$$, Mass number $$= 35$$

Question 15

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

Accepted Answer

$$	ext{Atomic mass} = (	ext{fraction}_1 	imes 	ext{mass}_1) + (	ext{fraction}_2 	imes 	ext{mass}_2) + (	ext{fraction}_3 	imes 	ext{mass}_3)$$

Question 16

Which of the following elements is most likely to form a $$2+$$ ion?

Accepted Answer

Magnesium (Mg)

Question 17

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

Accepted Answer

Elements are arranged in order of increasing atomic number.

Question 18

A sample of an unknown element contains atoms with 82 protons. What is the element and its symbol?

Accepted Answer

Lead, Pb

Question 19

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

Accepted Answer

A cation has a positive charge due to loss of electrons, while an anion has a negative charge due to gain of electrons.

Atoms and Elements: Structure, Properties, and the Periodic Table

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