Chapter 2 Test your understanding

6. 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- Answer:B

7. 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 Answer:C

2. Compared with 31P, the radioactive isotope 32P has?

(A) a different stomic number. (B) one more proton. (C) one more electron. (D) one more neuron. Answer:D

4. 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. Answer:A

3. The reactivity of an atom arises from?

(A) the average distance of the outermost electron shell from the nucleus. (B) the exsistense of unpaired electrons in the calence shell. (C) the sum of the potential energies of all the electron shells. (D) the potential energy of the valence shell. Answer:B

5. 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. Answer:D

1. In the term trace element, the adjective trace means?

(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 elememt enhances health but is not essential for the organism's long-term survival.