CHEMICAL COMPOUNDS AND FORMULAS

ELEMENTS

AN ELEMENT IS A PURE SUBSTANCE CONTAINING ONLY ONE KIND OF ATOM.

COMPOUNDS

COMPOUNDS:

• 2 OR MORE ELEMENTS CHEMICALLY COMBINED

• CREATES A NEW SUBSTANCE

MOLECULE

SUBSTANCE MADE OF TWO OR MORE ATOMS

CAN BE THE SAME ELEMENT OR DIFFERENT ELEMENTS

Element Molecule Compound

K

Au

Fe

Pb

I2

O2

CH4

H2O

H2O

CH4

C6H12O6

CaCO3

COMPOUNDS, MOLECULES, AND ELEMENTS

Compare and Contrast Molecules and CompoundsWhat do you notice?

• Compounds are 2 or more different atoms• Molecules are 2 or more atoms (can be the same or

different)

CHEMICAL COMPOUNDS

TWO OR MORE ELEMENTS CHEMICALLY COMBINED

AND FORMED BY CHEMICAL BONDS BETWEEN ATOMS.

IONIC BONDS: FORM IONS –

COVALENT BONDS: FORM MOLECULES

COMPOUNDS HAVE UNIQUE CHEMICAL AND PHYSICAL PROPERTIES.

THE PROPERTIES OF COMPOUNDS ARE VERY DIFFERENT FROM

THE PROPERTIES OF THE INDIVIDUAL ELEMENTS.

CHEMICAL FORMULAS

Chemical formulas describe compounds and list the atoms that are present in the compound.

NaCl – Sodium chloride (salt) – Na – Sodium, Cl - Chlorine

H2O – Dihydrogen monoxide (water) – H – Hydrogen, O - Oxygen –

CO2 – Carbon dioxide – C – Carbon, O - Oxygen

SUBSCRIPTS

NUMBERS WRITTEN BELOW AND TO THE RIGHT OF A CHEMICAL SYMBOL IN A FORMULA.

H2O – 2 HYDROGEN, 1 OXYGEN

• TELLS HOW MANY ATOMS OF AN ELEMENT ARE IN EACH MOLECULE.

• ONLY USED IF MORE THAN ONE ATOM IS PRESENT.

• CAN NEVER BE CHANGED IN A FORMULA

C9H8O4

C = CARBON – 9 ATOMS

H = HYDROGEN – 8 ATOMS

O = OXYGEN – 4 ATOMS

3 ELEMENTS 21 TOTAL ATOMS

H2SO4

H = HYDROGEN – 2 ATOMS

S = SULFUR – 1 ATOM

O = OXYGEN – 4 ATOMS

3 ELEMENTS 7 ATOMS

C12H22O11

C = CARBON – 12 ATOMS

H = HYDROGEN – 22 ATOMS

O = OXYGEN – 11 ATOMS

3 ELEMENTS 45 ATOMS

COEFFICIENTS• # PLACED IN FRONT OF A CHEMICAL SYMBOL OR FORMULA

• IDENTIFIES THE # OF MOLECULES OF A SUBSTANCE

2H2O = 2 MOLECULES OF H2O

2FEO3 = 2 MOLECULES OF FEO3

COEFFICIENTS X SUBSCRIPTS

• TO DETERMINE THE NUMBER OF ATOMS USING COEFFICIENTS YOU MULTIPLY THE COEFFICIENT WITH THE SUBSCRIPT.

• 2H2O - 2 MOLECULES OF H2O

= 4 HYDROGEN ATOMS AND 2 OXYGEN ATOMS

2FE2O3

• 2 MOLECULES OF FE2O3

=

• 2 X 2 = 4 FE (IRON) ATOMS

• 2 X 3 = 6 O (OXYGEN) ATOMS

COEFFICIENT PRACTICE: HOW MANY ATOMS ARE PRESENT?

Carbon: 2 atomsHydrogen: 8 atoms

Hydrogen: 2 atomsChlorine: 2 atoms

Hydrogen: 4 atomsOxygen: 4 atoms

USING PARENTHESES

• MULTIPLY THE SUBSCRIPT WITH EACH ELEMENT IN PARENTHESES.

• AL2(SO4)3

• AL = 2 ATOMS OF ALUMINUM

• S = 3 X 1 = 3 ATOMS OF SULFUR

• O = 4 X 3 = 12 ATOMS OF OXYGEN

(CH3)2CHOH

• C = CARBON = 2X1 = 2+1 = 3 CARBON ATOMS

• H = HYDROGEN = 3X2 = 6+2 = 8 HYDROGEN ATOMS

• O = OXYGEN = ONLY 1 OXYGEN ATOM

PARENTHESES

Ca

H

O

H

O

Calcium: 1 atomOxygen: 2 atomsHydrogen: 2 atoms

Chemical FormulasCheck out Potassium

Nitrate…

How many atoms of potassium are present?

KNO3How many atoms of nitrogen are

present?How many atoms of oxygen are present?

Now Ammonium Chloride…

NH4Cl

How many atoms of nitrogen are present?

How many atoms of hydrogen are present?How many atoms of chlorine are present?

Chemical Formulas

Check out Magnesium Hydroxide…

How many atoms of magnesium are present?

Mg(OH)2

How many atoms of oxygen are present?How many atoms of hydrogen are present?

Let’s take it up a notch…

Some formulas involve parenthesis. When this happens, multiply EVERYTHING inside the parenthesis by the subscript that is outside. The subscript outside can NEVER be changed.

Chemical Formulas

Check out Calcium Phosphate…

How many atoms of calcium are present?

Ca3(PO4)2

How many atoms of phosphorous are present?

How many atoms of oxygen are present?

Chemical FormulasCheck out the formula for aspirin…

How many atoms of carbon are present?

6C9H8O4

How many atoms of hydrogen are present?How many atoms of oxygen are present?

Let’s take it up a notch again…

The 6 in front of the formula is a coefficient. It tells how many molecules of a compound are present. You multiply the coefficient by EVERYTHING that comes after it.