• 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 (H2O).
• A cup of water contains millions of molecules of
H2O.
• 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.
MgSO4
• 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.
H2O
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.
N(CH3)3
• How many of each atom are there now?
• Answer: Nitrogen-1, Carbon-3, Hydrogen-9
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: CO3
This substance is carbonate
• In this image Hydrogen atoms are white and Nitrogen atom is
red.
• Write the chemical formula for this molecule.
Answer: NH3
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: C8H10N4O2
This substance is caffeine
•
•
•
•
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?
7H2O
• 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
2H2+O22H2O
• 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.
Yields
•2H2+O22H2O
Reactant
• 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.
CH4+O2CO2+H2O
• Count up the atoms in the products and reactants.
• How many carbons, hydrogens, and oxygens are on each side?
Are they equal?
CH4+O2CO2+H2O
C=1
H=4
O=2
They are
NOT equal
C=1
H=2
O=3
• 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
CH44+O
+O22CO
CO22+H
+2H
O
O
2 2
C=1
H=4
O=2
They are still
NOT equal
C=1
H=4
O=4
• 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
CO
+2H
O
CH44+2O
+O2CO
+2H
O
2
22
22
C=1
H=4
O=4
They ARE now
balanced
C=1
H=4
O=4
2H
H2+O22H
H2O
O
2
Fe+Cl2FeCl
2Fe+3Cl
2FeCl
3 3
2
Cu+2AgNO33Cu(NO
Cu(NO33)2)+2Ag
Cu+AgNO
+Ag
2
Zn+2HClZnCl
Zn+HClZnCl22+H
+H22
Pb(NO3)22+2AlCl
+AlCl33PbCl
PbCl2+2Al(NO
+Al(NO3)33
3Pb(NO