Chemical Formulas Symbol – abbreviation for the name of the element. Contain ONE capital letter followed by lowercase letter if necessary. Chemical Formula – combination of symbols showing what the molecule/ionic substance is made of and how many atoms in the molecule/ionic substance. -both qualitative and quantitative

Molecular Compounds Molecule – can be single atom, group of same atoms, or different elements (covalently bonded, almost always contain only nonmetals). -can be monatomic (one atom molecule), diatomic (two atom molecule), or polyatomic (many atom molecule)

Diatomic Molecules These seven elements occur naturally as molecules containing two atoms.

Types of Formulas Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound (ex. H2O2 = HO). Molecular formulas give the exact number of atoms of each element in a compound (ex. H2O2). Structural formulas show the way in which atoms are joined together in a molecule. ex.

Ions Ionic Bond – attractive force between ions resulting from the transfer of electrons of one atom to another. When atoms lose or gain electrons, they become ions. Cations are positive and are formed by elements on the left side of the periodic table (oxidation # = ionic charge) Anions are negative and are formed by elements on the right side of the periodic table (oxidation # = ionic charge)

Ionic Bonds Ionic compounds (most are salts such as NaCl) are generally formed between metals and nonmetals. -monatomic ions – one atom with a charge -polyatomic ions – group of atoms of more than one element with a charge (act as one unit) *atoms bond to achieve a stable octet – valence shell of s2p6 like a noble gas

Common Cations

Common Anions

Writing Formulas Binary Ionic Compounds 1. Write the symbol of the cation first, anion second 2. Determine the charge on the atoms of each element. 3. Select the subscripts that make the total positive charge equal to the total negative charge ex. Na2S

Multiple Oxidation States The cation that has multiple oxidation states must have a roman numeral which tells which oxidation state is used in the formula. ex: iron III oxide vs. iron II oxide

Writing Formulas Ternary Ionic Compounds Same as binary except polyatomic ions are used. Subscripts for polyatomic ions are placed outside the parentheses if necessary. ex. Ca(OH)2

Naming Ionic Compounds Write the name of the cation. If the anion is an element, change its ending to -ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion. If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses.

Naming Binary Molecular Compounds The less electronegative atom is usually listed first. A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however.)

Naming Binary Molecular Compounds The ending on the more electronegative element is changed to -ide. CO2: carbon dioxide CCl4: carbon tetrachloride

Naming Binary Molecular Compounds If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one: N2O5: dinitrogen pentoxide

Shortcut in Writing IONIC Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: The charge on the cation becomes the subscript on the anion. The charge on the anion becomes the subscript on the cation. If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.

International Union of Pure and Applied Chemists IUPAC International Union of Pure and Applied Chemists