2.2: Chem Formulas & Eqns

Chemical symbols make chemical formulas just as letters make wordsChemical formulas can be placed together to describe chemical rxns

2.2: Chem Formulas & Eqns

Chemical FormulaA shortened way using chemical symbols and numbers to represent a substance

Shows how many atoms are present in each molecule

2.2: Chem Formulas & Eqns

Chemical FormulaSubscripts are used to indicate how many of each atom are present

H2O2 hydrogen atoms1 oxygen atom

subscript

2.2: Chem Formulas & Eqns

Chemical FormulaSubscripts

If a subscript is not present with a chemical symbol, there is only 1 of that atom in the compound

2.2: Chem Formulas & Eqns

Formulas for Covalent CompoundsA covalent compound is made of 2 or more nonmetals

Prefixes are used to indicate the number of atoms of each element in the chemical formula

2.2: Chem Formulas & Eqns

Prefixes you must know

mono- 1 hexa- 6

di- 2 hepta- 7

tri- 3 octa- 8

tetra- 4 nona- 9

penta- 5 deca- 10

2.2: Chem Formulas & Eqns

Formulas for Covalent Compounds If the there is only 1 atom of the first nonmetal in a covalent compound, we do not usually use the prefix “mono”

CO2 – carbon dioxideSO3 – sulfur trioxide

2.2: Chem Formulas & Eqns

Formulas for Ionic CompoundsAn ionic compound is made of a metal and nonmetal

2.2: Chem Formulas & Eqns

Formulas for Ionic CompoundsTo write formula for an ionic compound, you need to figure out the charge that each ion will form

Use enough of each ion so the overall charge is 0

2.2: Chem Formulas & Eqns

Formulas for Ionic CompoundsTry this short cut:

Na1+ Cl1- NaCl

Mg2+ Cl1- MgCl2

2.2: Chem Formulas & Eqns

Chemical EqnsUses chemical symbols and formulas as a shortcut to describe a chemical rxn

Understood by scientists around the world

2.2: Chem Formulas & Eqns

Chemical EqnsReactants

The starting material in a rxnLeft side of equation

ProductsThe end material in a rxnRight side of the equation

2.2: Chem Formulas & Eqns

Chemical EqnsThe arrow is the “yield sign”, and separates the products and reactants

A plus (+) sign separates 2 or more reactants

2.2: Chem Formulas & Eqns

Balancing Chemical EqnsCoeffient

Numbers placed in front of chemical symbols or formulas

NEVER CHANGE SUBSCRIPTS WHEN BALANCING AN EQN

This changes the compound

2.2: Chem Formulas & Eqns

Chemical EqnsLaw of Conservation of Mass

Mass is neither created or destroyed in ordinary chemical or physical changes

Atoms must be equal on each side of a chemical equation