Q: Calculate the average atomic mass of an element that has two isotopes: 70.0% of isotope X-35 (mass = 34.97 amu) and 30.0% of isotope X-37 (mass = 36.97 amu).

$$(0.700 \times 34.97) + (0.300 \times 36.97) = 24.479 + 11.091 = 35.570$$ amu

Q: A sample of magnesium contains 78.99% $$^{24}\mathrm{Mg} (23.985 $$amu), 10.00% $$^{25}\mathrm{Mg} (24.986 $$amu), and 11.01% $$^{26}\mathrm{Mg} (25.983 $$amu). What is the average atomic mass of magnesium?

$$0.7899 \times 23.985 + 0.1000 \times 24.986 + 0.1101 \times 25.983 = 18.949 + 2.499 + 2.861 = 24.309$$ amu

Question 1

Which of the following statements is NOT a postulate of Dalton's Atomic Theory?

Accepted Answer

Atoms can be subdivided into protons, neutrons, and electrons.

Question 2

Which experiment led to the discovery that atoms have a small, dense, positively charged nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 3

A neutral atom of sodium 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 4

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons

Question 5

Which type of radiation is correctly matched with its charge?

Accepted Answer

$$\gamma$$ rays: no charge

Question 6

Calculate the average atomic mass of an element that has two isotopes: 70.0% of isotope X-35 (mass = 34.97 amu) and 30.0% of isotope X-37 (mass = 36.97 amu).

Accepted Answer

$$(0.700 	imes 34.97) + (0.300 	imes 36.97) = 24.479 + 11.091 = 35.570$$ amu

Question 7

Which of the following elements is a diatomic molecule in its natural state?

Accepted Answer

Oxygen ($$\mathrm{O}_2)$$

Question 8

Which of the following best explains why ionic compounds have high melting points?

Accepted Answer

They are composed of ions held together by strong electrostatic forces.

Question 9

What is the correct formula for a compound formed between aluminum and oxygen?

Accepted Answer

$$\mathrm{Al}_2\mathrm{O}_3$$

Question 10

Which of the following ions is isoelectronic with neon ($$\mathrm{Ne}$$)?

Accepted Answer

$$\mathrm{Na}^+$$

Question 11

A sample of magnesium contains 78.99% $$^{24}\mathrm{Mg} (23.985 $$amu), 10.00% $$^{25}\mathrm{Mg} (24.986 $$amu), and 11.01% $$^{26}\mathrm{Mg} (25.983 $$amu). What is the average atomic mass of magnesium?

Accepted Answer

$$0.7899 	imes 23.985 + 0.1000 	imes 24.986 + 0.1101 	imes 25.983 = 18.949 + 2.499 + 2.861 = 24.309$$ amu

Question 12

Which of the following is the correct name for $$\mathrm{FeCl}_3$$?

Accepted Answer

Iron(III) chloride

Question 13

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons

Question 14

Which of the following is a property of metals?

Accepted Answer

Forms cations by losing electrons

Question 15

What is the correct name for $$\mathrm{N}_2\mathrm{O}_5$$?

Accepted Answer

Dinitrogen pentoxide

Question 16

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

Accepted Answer

Elements in the same group have similar valence electron configurations.

Question 17

Which of the following is the correct formula for copper(II) sulfate pentahydrate?

Accepted Answer

$$\mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}$$

Question 18

Which of the following is the correct name for $$\mathrm{SO}_2$$?

Accepted Answer

Sulfur dioxide

Question 19

Which of the following ions has the same number of electrons as argon ($$\mathrm{Ar}$$)?

Accepted Answer

$$\mathrm{K}^+$$

Atoms, Molecules, and Ions: Foundations of Matter

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