The atomic number of sulfur is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound.
a. HS
b. HS₂
c. H₂S
d. H₄S

Which of the following statements correctly describes any chemical reaction that has reached equilibrium?

a. The concentrations of products and reactants are equal.

b. The reaction is now irreversible.

c. Both forward and reverse reactions have halted.

d. The rates of the forward and reverse reactions are equal.

Which statement is true of all atoms that are anions?

a. The atom has more electrons than protons.

b. The atom has more protons than electrons.

c. The atom has fewer protons than does a neutral atom of the same element.

d. The atom has more neutrons than protons.

Draw Lewis dot structures for each hypothetical molecule shown below, using the correct number of valence electrons for each atom. Determine which molecule makes sense because each atom has a complete valence shell, and each bond has the correct number of electrons. Explain what makes the other molecule nonsensical, considering the number of bonds each type of atom can make.

What coefficients must be placed in the following blanks so that all atoms are accounted for in the products?

C₆H₁₂O₆ → _____C₂H₆O + _____CO₂

a. 2; 1

b. 3; 1

c. 1; 3

d. 2; 2

We can represent atoms by listing the number of protons, neutrons, and electrons—for example, 2p+, 2p+,2n0,2e− for helium. Which of the following represents the ¹⁸O isotope of oxygen?

a. 7p+, 2n0, 9e−

b. 8p+, 10n0, 8e−

c. 9p+, 9n0, 9e−

d. 10p+, 8n0, 9e-