Chemical formulas indicate the relative number of atoms of each kind element in a chemical compound (ionic and molecular) Ionic compound the number of atoms in a formula units NaCl Molecular compound the number of atoms in a molecule CH 3 Cl Subscript # atoms Capital letter each element

Monatomic ions - ions formed from a single atomNa + orS 2- usually tell by column on periodic table, some elements have more than one oxidation number or charge Binary compounds- only 2 elements in the compound Na 2 S Polyatomic ions - ions formed from more than one type of atom covalently bonded together OH - PO 4 3- NH 4 + Ionic Compounds

Quiz yourself How many oxygen atoms in the following? –CaCO 3 –Al 2 (SO 4 ) 3 How many ions in the following? –CaCl 2 –NaOH –Al 2 (SO 4 ) 3

Rules for writing formulas for ionic compounds 1. when making the formula the cation (positive ion) always goes 1 st then the anion (negative ion) 2. the compound is neutral + = - charge 3. subscripts added to make charges cancel 4. When adding subscript to polyatomic ion it is put in ( )’s 5. Formula unit is always the simplest ratio of ions must ÷ subscripts

The positive side of the formula must = the negative side of the element Examples on board 1. Sodium chloride Na + Cl - NaCl ( no charges written in the formula) 2. Calcium cholride Ca 2+ Cl - CaCl 2 3. Potassium sulfideK + S 2- K 2 S

4. Aluminum chlorideAl 3+ Cl - AlCl 3 5. Barium phosphateBa 2+ PO 4 3- Ba 3 (PO 4 ) 2 Cross over method - the charges become the subscripts of the other ion Beware subscripts must be simplest ratios

Naming ionic compounds (stock system) 1. Binary compound - 2 elements when naming the compound the name of the first element(+ion) stays the same the last element ends in “ide” example NaCl sodium chloride

Formula: ZnS Compound Name: Zinc Sulfide

2. Polyatomic ions- use their own name ( on ion sheets). Example NH 4 Cl ammonium chloride Ba 3 (PO 4 ) barium phosphate Na OH sodium hydroxide

Stock System 3. Elements with more than one oxidation number (charge) -put the oxidation number in Roman numerals in ( )’s Example Pb(NO 3 ) 2 lead (II) nitrate Usually transition metals have more then one oxidation number also lead and tin Check ion sheet

Molecular Compounds- made of neutral atoms sharing electrons & form neutral molecules 2 types of formulas molecular formula- represents a molecule C 6 H 6 empirical formulas - simplest ratio of atoms (formula units are always empirical formulas) CH

diatomic molecule - 2 atoms of the same element covalently bonded together H 2 N 2 O 2 F 2 Cl 2 Br 2 I 2 There are 7 diatomic elements and they form the shape of a 7 on the periodic table except for H which is always an oddball Only diatomic when pure element not necessarily when forming a compound

Use prefixes to name molecular compounds prefix subscript monono subscript (1 atom) di 2 tri3 tetra4 penta5 hexa6 hepta7 octa8 nona9 & deca10

Rules for molecular compounds 1. The less electronegative element is given 1st and only given a prefix if it has a subscript >1 (never start a name with mono) 2. Second element- add a prefix and add “ide” (drop prefix ending if first letter in the name of the element is a vowel) P 4 O 10 tetraphosphorous decoxide

Oxidation Numbers In polar covalent bonds, the electrons are located closer to one atom than the other. This is reflected in a partial charge,  + and  -, for each atom. The oxidation state or oxidation number of an atom is an indication of the amount of charge each atom carries. The one with the greater EN gets both e -

Example: We know that in HCl, H has a lower EN and is  + and Cl has a greater EN is  -. We say H is in the +1 oxidation state and Cl is in the  1 oxidation state.

Acids endings change “-ate” to “-ic” H 2 SO 4 sulfuric “-ite” to “-ous” H 2 SO 3 sulfurous Important acids to know: HCl hydrochloric HNO 3 nitric H 3 PO 4 phosphoric HC 2 H 3 O 2 acetic (also CH 3 COOH) H 2 CO 3 carbonic