CHAPTER 6- CHEMICAL NAMES AND FORMULAS

KEY TERMS

Anion- Any atom or group of atoms with a negative charge.

Binary Compound- A compound composed of two elements; NaCl and Al2O3 are binary compounds.

Cation- Any atom or group of atoms with a positive charge.

Chemical formula- Shows the number and type of atoms present in the smallest representative unit of a substance; the chemical formula of ammonia, with one nitrogen and three hydrogens, is NH3.

Formula unit- The lowest whole-number ratio of ions in an ionic compound; in magnesium chloride, the ratio of magnesium ions to chloride ions is 1: 2 and the formula unit is MgCl2.

Ion- An atom or group of atoms that has a positive or negative charge; cations are ions with a positive charge, and anions are ions with a negative charge.

Ionic compound- A compound composed of positive negative ions.

Law of definite proportions- If any sample of a chemical compound, the elements are always combined in the same proportion by mass.

Law of multiple proportions- Whenever two elements form more than one, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.

Molecular compound- A compound that is composed of molecules.

Molecular formula- A chemical formula that shows the actual number and kind of atoms present in a molecule of a compound.

Molecule- A neutral chemically bonded group of atoms that act as a unit.

Monatomic ion- A single atom with a positive or negative charge as a result of losing or gaining valence electrons.

Polyatomic ion- A tightly bound group of atoms that behaves as a unit and carries a charge.

Ternary compound- A compound containing atoms of three different elements, usually containing at least one polyatomic ion; Na2CO3 and Mg(OH)2 are ternary ionic compounds.

SUMMARY

Every substance is either an element or a compound. A compound consists of more than one kind of atom. A compound is either molecular or ionic in nature. Molecular compounds are composed of two or more nonmetals. A molecular formula shows the number and kinds of atoms present in a molecule of a compound. Ionic compounds are composed of oppositely charged ions (cations and anions) combined in electrically neutral groupings. A formula unit gives the lowest whole-number ratio of ions in the compound. The charges of the ions of the representative elements can be determined by the position of these elements in the periodic table. Most transition metals have more than one common ionic charge. A polyatomic ion is a group of atoms that behaves as a unit and has a charge. Binary (two-element) ionic compounds are named by writing the name of the cation followed by the name of the anion. Binary compounds end in –ide. When a cation can have more than one ionic charge, a Roman numeral is used in the name. Ternary ionic compounds contain at least one polyatomic ion. The names of these compounds generally end in –ite or –ate. Binary molecular compounds are composed of two nonmetallic elements. The name of a binary molecular compound always ends in –ide-. Prefixes are used to show how many atoms of each element are present in a molecule of the compound. The use of a flowchart is helpful in naming compounds.

To test your chemistry skill, try the practice test