We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A cup of water contains millions of molecules of H 2 O.

Chemical, or molecular, formulas are a concise way of expressing information about the atoms that constitute a particular chemical compound. Wait…what? It is an expression which states the number and type of atoms present in a molecule of a substance.

MgSO 4

A subscript is used to represent the number of each atom being represented. If only one atom is represented, there is no subscript. In the formula for water, what is the subscript? There is only one atom of Oxygen, so it does not have a subscript. H2OH2OH2OH2O H = Hydrogen O = Oxygen

Usually the subscript just multiplies or shows the number of atoms of a single element. If the subscript exists outside of a set of parenthesis then it will multiply the atoms of all of the elements inside the parenthesis. How many of each atom are there now? Answer: Nitrogen-1, Carbon-3, Hydrogen-9 N(CH 3 ) 3 N = Nitrogen C = Carbon H = Hydrogen

In this image the Carbon atom is blue and the Oxygen atom is red. Write the chemical formula for this molecule. Answer: CO This substance is carbon monoxide

In this image the Carbon atom is black and the Oxygen atoms are red. Write the chemical formula for this molecule. Answer: CO 3 This substance is carbonate

In this image Hydrogen atoms are white and Nitrogen atom is red. Write the chemical formula for this molecule. Answer: NH 3 This substance is ammonia

In this image blue represents Nitrogen atoms, red represents Oxygen atoms, white represents Hydrogen atoms and black represents Carbon atoms. Write the chemical formula for this molecule. Answer: C 8 H 10 N 4 O 2 This substance is caffeine

7H 2 O Coefficients appear on the left side of a chemical formula. They are used to multiply all the atoms in a compound In the following formula, which is the coefficient? Earlier we learned that the subscript 2 meant that there were two Hydrogen atoms. The coefficient 7 means there are 7 times more. How many Hydrogen atoms do we have? How many Oxygen atoms? 7H2O7H2O

representation of chemical reaction in equation: a representation, using chemical symbols in a form resembling a mathematical equation, of the process involved in a chemical reaction This is an example of a chemical equation. The components on the left combine together to yield (represented by the arrow) the component on the right. 2H 2 +O 2  2H 2 O

Reactant Product Yields

Atoms are neither created, nor destroyed, during any chemical reaction. This means that the same number of atoms that are present after a reaction are the same number of atoms that are present before a reaction. There is only a rearrangement

Write out your “un-balanced” equation using formulas of reactants and products. CH 4 +O 2  CO 2 +H 2 O

Count up the atoms in the products and reactants. How many carbons, hydrogens, and oxygens are on each side? Are they equal? CH 4 +O 2  CO 2 +H 2 O C=1 H=4 O=2 C=1 H=2 O=3 They are NOT equal

Since our carbons are ok we will not mess with those now. However, we have half the number of hydrogens in the products than we do in the reactants. What do we need to add? Where do we add it? CH 4 +O 2  CO 2 +H 2 OCH 4 +O 2  CO 2 +2H 2 O C=1 H=4 O=2 C=1 H=4 O=4 They are still NOT equal

Now we have half the number of Oxygens. What do we need to add? Where do we need to add it? Is everything equal now? CH 4 +O 2  CO 2 +2H 2 O CH 4 +2O 2  CO 2 +2H 2 O C=1 H=4 O=4 C=1 H=4 O=4 They ARE now balanced

H 2 +O 2  H 2 O2H 2 +O 2  2H 2 O

Fe+Cl 2  FeCl 3 2Fe+3Cl 2  2FeCl 3

Cu+AgNO 3  Cu(NO 3 ) 2 +Ag Cu+2AgNO 3  Cu(NO 3 ) 2 +2Ag

Zn+HCl  ZnCl 2 +H 2 Zn+2HCl  ZnCl 2 +H 2

Pb(NO 3 ) 2 +AlCl 3  PbCl 2 +Al(NO 3 ) 3 3Pb(NO 3 ) 2 +2AlCl 3  3PbCl 2 +2Al(NO 3 ) 3