Chemical Names and Formulas Molecules and Molecular Compounds 1.Molecule- the smallest electrically neutral unit of a substance that still has the properties of the substance 2.Molecular compound- a compound that is composed of molecules (two or more nonmetals)

Characteristics of molecular compounds  Representative unit- molecule  Type of elements- nonmetals  Physical state- solid, liquid or gas  Melting point- low

Ions and Ionic Compounds 1.Ion- atoms or groups of atoms with a charge. Ions form when an atom or group of atoms gain or lose electrons a. cation- a positive ion formed when an atom loses electrons. A positive ion would have the same name as a normal atom a. cation- a positive ion formed when an atom loses electrons. A positive ion would have the same name as a normal atom Example- Na and Na + Example- Na and Na + sodium atom sodium ion sodium atom sodium ion Even though they have the same name, they have different chemical properties Even though they have the same name, they have different chemical properties

Ions and Ionic Compounds b. anion- a negative ion formed when an atom gains electrons. The name of an anion is changed to -ide Example: Cl and Cl - Example: Cl and Cl - chlorine atom chloride ion chlorine atom chloride ion

Is the compound ionic or molecular 1.NaCl 2.N 2 O 3.SO 2 4.MgCl 2 5.CCl 2

Name each atom or ion 1.Mg 2.Li 3.Mg +2 4.Li +1 5.Cl 6.Br 7.Cl -1 8.Br -1

Ionic compounds Ionic compound- composed of metals and nonmetals (cations and anions) Characteristics Representative Unit -formula unit Type of elements -metals- nonmetals Physical State - solids Melting Point - high

Representing Chemical Compounds 1.Chemical Formula- show the kinds and numbers of atoms in the smallest representative unit of a substance Examples: O 2, N 2 A. Molecular Formula- shows the kinds and numbers of atoms in a molecule of a compound. (groups of nonmetals) Examples: CO 2, H 2 O B. Formula Unit- lowest whole-number ratio of ions in an ionic compound. (metals and nonmetals) Examples: MgCl 2, AlCl 3

Ionic Charges  Ionic compounds are electrically neutral  The charges on the anions and cations in the compound equal zero

Ionic Charges Group 1A ions = +1 Group 2A ions = +2 Group 3A ions = +3 Group 4A usually do not form ions Group 5A ions = -3 Group 6A ions = -2 Group 7A ions = -1

Transition Metals- can have more than one charge, a Roman numeral in parenthesis indicates the numerical value of the charge

Exceptions- Ag is always +1,cadmium and zinc are always +2 Practice: What is the charge of each ion typically formed by each element? 1.Sulfur 2.Lead, 4 electrons lost 3.Strontium 4.Argon 5.Bromine 6.Copper, one electron lost