Explain why lattice energy is the key to the formation of a salt.

Why are ionic solids hard?

An ionic bond forms when:

a. atoms share electrons.

b. positively charged and negatively charged parts of polar covalent molecules attract.

c. ions with opposite electrical charges attract.

d. two atoms exchange protons.

e. an element has two types of isotopes.

How could each of the following atoms react to achieve a noble-gas configuration? a. iodine, b. strontium, c. nitrogen, d. krypton.

The electron affinity for chlorine has a negative value, indicating that the atom readily accepts another electron. Why does a chlorine atom readily accept another electron?

The electron configuration for arsenic, As, is $[\mathrm{Ar}] 3 d^{10} 4 s^{2} 4 p^{3}$. How many valence electrons does an As atom have? Write the symbol for the ion it forms to achieve a noble-gas configuration.

To achieve a noble-gas configuration, a phosphorus atom will form a $P^{3−}$ anion rather than forming a $P^{5+}$ cation. Why?

A restaurant offers a dinner special that lets you choose from 12 entrees, 10 side dishes, and 6 desserts. You can choose one entree, two side dishes, and one dessert. How many different meals are possible?

In a maternity ward, four babies become accidentally mixed up. The ABO types of the four babies are known to be O, A, B, and AB. The ABO types of the four sets of parents are determined. Indicate which baby belongs to each set of parents:

$$\text { (a) } A B \times O , ( b ) A \times O , ( c ) A \times A B \text { (d) } \mathrm { O } \times \mathrm { O }$$

Why do the properties of an ion differ from those of its parent atom?

How does the octet rule help predict the chemical reactivity of an element?

Explain why only a few metals are found in nature in their pure form, while most exist only as ores, which are metal-containing compounds.

What property do the noble gases share? How do the electron configurations of the noble gases give them this shared property?

Which of the following is NOT an endocrine gland?

(A) thyroid gland

(B) pituitary gland

(C) parathyroid gland

(D) sweat gland

(E) adrenal gland