Chemical Formula Notes

TEKS 8.5D recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts TEKS 8.5F recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass

Atoms are the basic units of matter. Atoms join together chemically to form elements.

Elements are pure substances made of only one kind of atom.

Elements are represented by 1-2 letters called symbols on the Periodic Table.

Molecule is a term used to refer to 2 or more atoms which are bonded. Examples are O2 and CO2.

CO2 is both a molecule and a compound as well.

Compounds are substances made of two or more different elements chemically combined in a set ratio.

A chemical bond, or electric force, holds the atoms together in a compound.

The properties of a compound are totally different from the

elements that make up the compound.

+ = carbon oxygen carbon dioxide

For example, salt is composed of sodium (Na); a silvery metal; and chlorine (Cl); a stinky, green gas.

Salt=> (1 sodium, 1

chlorine)

When the two elements bond to form NaCl, they form solid white crystals which you can eat!

Chemical formulas are used to show the ratio of elements in a compound. The elements present in a compound are identified with the element’s symbol.

Chemical formula

If more than 1 atom of an element is in the compound, it is shown with a subscript.

O 2

For example, water; H2O; has 2 atoms of hydrogen. Since oxygen has no subscript, there is only 1 atom of oxygen

Sometimes, substances contain more than 1 molecule of an individual compound.

This is shown with a coefficient. Coefficients are written in front of the compound’s formula.

H2 4

For example, 2SO3 means there are 2 molecules of sulfur oxide. The total number of the atoms in 2SO3 would be 8; 2 atoms of sulfur and 6 atoms of oxygen.

Compound Name Elements present Total # of atoms # of molecules

H2O water 2-hydrogen 1-oxygen 3 1

ZnCO3 zinc carbonate 1-zinc

1-carbon 3-oxygen

5 1

Al2O3 aluminum

oxide 2-aluminum

3-oxygen 5 1

3Na2SO3 sodium sulfate 6-sodium 3-sulfur

9-oxygen 18 3

C6H12O6 glucose 6-carbon

12-hydrogen 6-oxygen

24 1

CH4 methane 1-carbon 4-hydrogen 5 1

2HCl hydrochloric acid

2-hydrogen 2-chlorine 4 2