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aqueous solution (aq) is hydrofluoric acid.

 The formulas and systematic names for a selection of common strong acids.

Acid Formula Non-metal Present in Acid Systematic Name HCl(aq) Chloride Hydrochloric acid HBr(aq) Bromide Hydrobromic acid HI(aq) Iodide Hydroiodic acid

HNO3(aq) Nitrate Nitric acid H2SO4(aq) Sulfate Sulfuric acid

Diatomic Elements

Diatomic elements do not have full valence electron shells and cannot exist as a single atom. For example, the reactivity of hydrogen causes lone atoms to combine into diatomic (two atom) molecules forming hydrogen gas (H2(g)) or liquid hydrogen (H2(l)). Element names ending in “-gen” or “-ine” are diatomic. The names and formulas for the seven diatomic elements can be found in Table 4.

Note: These elements are diatomic ONLY when they are the only element present, NOT when they are chemically bonded to other elements.

Table 4. The formulas and names of the seven diatomic elements.

Seven Diatomic Elements

Hydrogen H2 Nitrogen N2 Oxygen O2 Fluorine F2 Chlorine Cl2

Bromine Br2

Iodine I2

Review and Tips

In the Exercises, you will study the periodic table and familiarize yourself with polyatomic ions, common acids, and the diatomic elements. Then, you will practice the discipline of following a set of rules to write the names and formulas of ionic and molecular compounds. It is important to follow all of the rules and not to skip steps. Do not go too fast, or guess at names, charges, or formulas. If you guess incorrectly you may learn or memorize the rules incorrectly. Review the flowchart in Figure 7 for help differentiating between molecular and ionic compounds.