CHEMICAL FORMULAS AND

EQUATIONS

CHEMICAL FORMULAS Formulas use chemical symbols and

numbers for qualitative and quantitative information

Symbol = qualitative (element)Example, CO

Subscript = quantitative (amount) Example, CO2

TYPES OF FORMULAS There are two types of formulas,

empirical and molecular. The empirical formula represents the

simplest integer ratio in which atoms combine to form a compound.

Ionic compounds do not form molecules, so ionic formulas indicate a ratio of ions. Example, NaCl (1 sodium and 1 chlorine ion)Example, MgCl2 (1 magnesium and 2

chlorine ions) Formulas of ionic substance are

empirical

TYPES OF FORMULAS Molecular formulas may be a multiple of

the empirical formula. Covalently bonded substances form

molecules. A molecular formulas represents the

actual ratio of atoms in a molecule. Example, glucose is C6H12O6, but that

formula can be reduced to CH2O

ATOMS, COMPOUNDS, AND IONS Atoms and compound are electrically

neutral. In an atom protons = electrons In a compound the charges balance out. Ions are not neutral and may be either

positive or negative (cations and anions) An ionic charge is indicated by a

superscript. A sodium ion with a charge of 1+ is written

as Na+ (this is known as the oxidation state) Some atoms have more than one oxidation

state

POLYATOMIC IONS A polyatomic ion is a group of atoms

covalently bonded together possessing a charge.

Parentheses are used to enclose polyatomic ions when there is more than one of the ions in a compound.

A subscript after the parentheses tells how many polyatomic ions are present.

COEFFICIENTS A coefficient written in front of a formula

tells how many units of the formula are present and it applies to the entire formula

Example, 2H2O The elements present are: hydrogen and oxygen In water there are two hydrogens for every one

oxygen In 2H2O there are actually 4 hydrogen atoms and

2 oxygen atoms

How many of each atom in: 4 Ca(NO3)2

WHAT IS A HYDRATE A hydrate is formed when water gets

trapped with in the crystal lattice structure of an ionic compound.

These crystals have a definite number of water molecules for each unit of the compound

An anhydrous (opposite of hydrated) compound can be obtained by heating the crystals to drive off water.

In a chemical reactions, the water in the hydrate does not react, but it adds mass to the compound.

WRITING FORMULAS AND

NAMING COMPOUNDS

EQUALIZING CHARGES Compound are considered neutral by

having an equal number of positive and negative charges.

The criss-cross method is used to help figure out the correct formula when equalizing charges. Remember to transfer only the number and

not the sign and do not write the number 1

NAMING COMPOUNDS Compounds are named based on the

types of elements that form them. Ionic compounds are named by one

method. Covalent compounds that contain only

nonmetals are named differently.

BINARY IONIC COMPOUNDS The names of binary ionic compounds

come directly from the elements in the compound.

The positive particle (the metal) is placed first.

The negatively charged ion will end the formula.

The metal’s name remains the same and the nonmetal gets an –ide ending. Example, NaCl is sodium chlorideExample, CaBr2 is calcium bromide

IONIC COMPOUNDS WITH POLYATOMIC IONS Naming these kinds of compounds is

simple, just simple use the metal’s name and the polyatomic ions name.

Nothing needs to modified. Example: NaOH is sodium hydroxide

BINARY COVALENT COMPOUNDS A binary compound that contains two nonmetals

is arranged by electronegativity values. The element with the lower electronegative

value is written first. The name of the compound will end in –ide. These elements can often form more than one

compound, so a prefix is used to tell the reader how many atoms of each element are present. Example, CO is carbon monoxide Example, CO2 is carbon dioxide

If there is only one atom of the first element in the compound a prefix is not needed

THE STOCK SYSTEM Some metals (transition metals) have

more than one oxidation state. The stock system solves this problem by

simply stating the oxidation number by using Roman numerals after the name of the metal. Example, Iron (II) chloride tells the reader

that the iron has an oxidation number of +2 and the formula would be FeCl2

What would Iron (III) chloride look like?

CHEMICAL REACTIONSPhysical Change A change in the

appearance of the starting material

Phase changes are physical changes

Ex, melting, freezing, boiling

Chemical Change A change in which

the products are a different material than the reactants

Chemical reactions are chemical changes

Ex, burning, rusting

CHEMICAL EQUATIONS A chemical equation is used to show

what takes place during a chemical reaction.

The starting substance is called the reactant (located on the left side of the arrow)

The substance produced is called the product (located on the right side of the arrow)

H2 (g) + O2 (g) 2H2O (g)

ENDOTHERMIC AND EXOTHERMIC Chemical and physical changes involve

the loss or gain of energy. Endothermic – heat is absorbed during

the reaction Exothermic – heat is released during the

reaction

Type of reaction

Surrounding temperature

Potential Energy of the Reactants

Potential Energy of the Products

Value of Delta H

Endothermic Decreases Less More Positive

Exothermic Increases More Less Negative

ENDOTHERMIC Process that requires energy in order for

a chemical reaction to occur. Physical change – ice melting Chemical change – food cooking The reactants absorb energy as they

become products. The products have more potential

energy than the reactants.

EXOTHERMIC Process that release energy when a

chemical reaction occurs. Physical change – water freezing Chemical change – combustion The reactants release energy as they

become products. The products have less potential energy

than the reactants.

BALANCING CHEMICAL REACTIONS The Law of Conservation of Mass: mass

of the products = the mass of the reactants

There also has to be conservation of atoms

Coefficients in equations tells us how many atoms or molecules are present (Moles)

TYPES OF REACTIONS Synthesis reactions Decomposition reactions Single replacement reactions Double replacement reactions

SYNTHESIS REACTIONS When two or more reactants combine to

form a single product

A + B AB

A and B represent either elements or compounds and AB represents a compound

DECOMPOSITION REACTION The reverse of a synthesis reaction in

that a single compound is broken into tow or more simpler substances

AB A + B

A and B represent either elements or compounds and AB represents a compound

SINGLE REPLACEMENT REACTIONS A type of reaction where one element replaces

another element in a compound. This type of reaction always involves an

element and a compound.

A + BC B + AC

One can predict whether a reaction will happen or not using the Activity Series

A metal listed on the table will react with the compound of a metal below it.

A nonmetal will replace a less active nonmetal in a compound

DOUBLE REPLACEMENT REACTION These reactions generally involve two

soluble ionic compounds that react in solution to produce a precipitate, a gas, or a molecular compound

AB + CD AD + CB

There are three ways to determine if a double replacement reaction will occur

DOUBLE REPLACEMENT REACTION1) The reaction will occur if one of the

products is a solid. If one product is insoluble then the reaction will occur.

2) The reaction will occur if one of the products is a gas.

3) The reaction will occur if one of the products is water.