In the term trace element, the adjective trace means that a. the element is required in very small amounts. b. the element can be used as a label to trace atoms through an organism's metabolism. c. the element is very rare on Earth. d. the element enhances health but is not essential for the organism's long-term survival.

We can be sure that a mole of table sugar and a mole of vitamin C are equal in their a. mass. b. volume. c. number of atoms. d. number of molecules.

The reactivity of an atom arises from a. the average distance of the outermost electron shell from the nucleus. b. the existence of unpaired electrons in the valence shell. c. the sum of the potential energies of all the electron shells. d. the potential energy of the valence shell.

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.

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.

We can represent atoms by listing the number of protons, neutrons, and electrons—for example, 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-

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

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

DRAW IT 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. a.