Download Finding the Mass of Compounds Notes

Finding the Mass of Compounds Notes
What are compounds?
- Compounds are composed of 2 or more
atoms bonded together forming a single unit
Examples…
- H2O, NH3, Br2, C6H12O6, and NaCl
There are two main types of
compounds
To summarize:
1. Molecules: compounds composed of
atoms connected by covalent bonds (sharing
of electrons, usually between nonmetals)
2. Ionic Compounds (Formula Units):
compounds composed of atoms connected
by ionic bonds (giving up and accepting
electrons, occurs between metals and
nonmetals).
Compounds
Molecules
Covalent bonds
Chemical Formulas:
Ionic Compounds
Ionic Bonds
- designed to represent the number and types
of elements in a compound.
Important numbers in chemical
formulas:
1. Subscript
Example
- indicates the number of atoms of each type
of elements in a compound
H2O
and
CH4
Subscripts
written in the lower right-hand corner of
the element it represents
- If only one atom of an element is in the
compound, no subscript is written  in
the absence of a subscript, assume the
number is one.
Ca(NO3)2
- The () surround the NO3 portion of the
compound; the subscript 2 is in the lower right
hand corner of the (). The parentheses and
subscript indicate that that portion of the
compound appears twice in the formula
NO3-1–-Ca 2+– NO3-1
-In other words, there are two sets of NO3
molecules in this compound.
To determine the number of N and O, multiply
your subscripts (N 1 x 2 = 2 N, O 3 x 2 = 6 O)
-
Another example
What do the parentheses
indicate in this chemical
formula?
2. Coefficient
Example
- indicates number of compounds or moles
present in a chemical reaction
N2 + 3 H2  2 NH3
Coefficients
- written in normal script to the left of the
compound it represents
- If no coefficient is present assume the
number is one.
- Coefficients are used to group like molecules
in a chemical reaction making it easier to read.
Without Coefficients 
N2 + H2 + H2 + H2  NH3 + NH3
With Coefficients  N2 + 3 H2  2 NH3
How to find the mass of a
compound –
4 Steps to finding the
1. Take inventory of the elements in the
mass of a compound
compound (write out the element’s
symbol and the number of atoms of that
element)
2. Find the average atomic mass of each
element using your periodic table
3. Multiply the number of each element by
its atomic mass
4. Add up all the masses.
Examples
Find the mass of C6H12O6:
Step 1: C = 6
H = 12
O= 6
Step 2: C = 6
12.01
H = 12
1.01
O= 6
16.00
Step 3: C = 6 x 12.01 = 72.06
H = 12 x 1.01 = 12.12
O = 6 x 16.00 = 96.00
Step 4: C = 6 x 12.01 = 72.06
H = 12 x 1.01 = 12.12
O = 6 x 16.00 = +96.00
180.18
Mass of C6H12O6 is 180.18 amu
Final example
Find the mass of Sr(CO3)2
Step 1: Sr = 1
C=2
O= 6
Step 2: Sr = 1
87.62
C=2
12.01
O= 6
16.00
Step 3: Sr = 1 x 87.62 = 87.62
C = 2 x 12.01 = 24.02
O = 6 x 16.00 = 96.00
Step 4: Sr = 1 x 87.62 = 87.62
C = 2 x 12.01 = 24.02
O = 6 x 16.00 = +96.00
207.64
Mass of Sr(CO3)2 is 207.64 amu