Chapter 3
Atoms to Molecules
A mass spectrometer can measure
relative masses of isotopes.
For example, the ratio of the mass
13
12
of C to C is found to be
13
Mass C
=1.0836129
12
Mass C
So we can say
the mass of 13C = (1.0836129)(12 amu) = 13.003355 amu
Average Atomic Mass
(AAM)
AAM = (f1)(m1) + (f2)(m2) + (f3)(m3) + …
fn = fractional abundance of isotope n
mn = mass of isotope n (in amu)
Ex.// Copper has two naturally occurring
isotopes: 63Cu ( 62.929599 amu, 69.17%)
and 65Cu(64.927793 amu, 30.83%). What is
the AAM of copper?
63.55 amu
Ex.// Nitrogen has two naturally occurring isotopes,
14
N (14.003074002 amu) and 15N (15.000108898
amu). What are the percent abundances of the two
isotopes of nitrogen? (AAM of N = 14.00674 amu)
N = 99.632%
15
N = 0.368 %
14
A mole is defined as the number of
12
atoms in exactly 12 grams of C.
1 mole _____ = 6.0221418 x 10 23 ______
Avogadro’s Number, NA, is 6.0221418 x 1023
The mass of 1 mole of something is
called it's molar mass.
The units are usually taken as g/mol.
The molar mass of any element is numerically equal to its
AAM.
For example, the molar mass of carbon is 12.011 g/mol.
To find the molar mass of a compound, add up the molar
masses of all atoms that make up the compound.
For example, we calculate the molar
mass of CO2 this way:
C = 12.011 g/mol
O = 15.9994 g/mol
CO2 = 12.011 g/mol + 2(15.9994 g/mol) = 44.010
We can combine what we know
about the mole and molar mass.
For example, we can find how many atoms of
nitrogen, and how many atoms of hydrogen
there are in 3.141 grams of N 2H4.
We use molar mass to find how many moles we
have.
For every mole of N2H4 we have we have 2 moles of
N and 4 moles of H.
Now we use Avogadro's number to convert moles to
individual atoms.
1.181 x 1023 atoms of N
2.361 x 1023 atoms of H
Molarity (M) is a measure of how
many moles of something is in a liter
of solution.
n
M=
V
What is the [CoCl2] in a solution that is
made by dissolving 3.141g of CoCl2 in
enough water to make 100.0 mL of
solution?
0.2419 M
Ions make ionic compounds, molecules
are made from only nonmetals.
An ion is an atom that has lost or gained one or
more electrons
When we add more solvent to a
solution we dilute it.
M1V1 = M2V2
What is the [NaNO3] in a solution that is
made by dissolving 0.6158 g of NaNO3 in
enough water to make 75.00 mL of solution,
then diluting 5.00 mL of this solution to 125.0
mL?
0.00386 M
A chemical equation describes a
chemical reaction.
C2H6O (l ) + 3O2(g)
2CO2(g) + 3H2O(g)
Coefficients
Phases
Balancing
We have different systems of
nomenclature. The common
naming system is one...
Water - H2O (MEMORIZE)
Ammonia - NH3 (MEMORIZE)
Baking Soda - NaHCO3
Brimstone - S
Grain Alcohol - C2H5OH
Laughing Gas - N2O
We have a more systematic method
now. Let's start simple, with
elements.
For most elements the name is just the name
of the element and the formula is just the
symbol.
There are some elements that are diatomic:
HOFBrINCl
Monatomic Cations
Formed by the loss of 1 or more electrons
from a neutral element.
Name is the same as the neutral element.
If that element can form more than one
cation, use a Roman Numeral.
Mercury is special: mercury (I) versus mercury (II)
Figure 3.9 pg. 130 shows some
common ions. MEMORIZE IT.
Monatomic Anions
Formed by adding 1 or more electrons
to a neutral element.
Anions consisting of only 1 element
are named by changing the ending of
the element’s name to “ide”.
Binary Ionic Compounds
One metal element and one
nonmetal element.
The cation is the first element, the
anion is the second.
The name of a binary ionic
compound is:
Name of cation + name of anion
Binary Molecular Compounds
2 nonmetal elements.
The name of a binary molecular
compound is:
Name of first element, then
name of second element,
ending changed to “ide”
USE PREFIXES
MEMORIZE TABLE 3.6 Pg. 132
No “mono” for first element
Ternary Ionic Compounds
3 or more different elements in the
compound.
The cation (usually a metal, but could be a
polyatomic ion), is written first.
The anion (usually a polyatomic ion) is
written second.
The name of a ternary ionic compound is:
Name of cation + name of anion
MEMORIZE TABLE 3.5 pg. 129
+
8 OTHERS
BrO−
BrO2−
hypobromite
bromite
BrO3−
bromate
BrO4−
perbromate
IO−
IO2−
hypoiodite
iodite
IO3−
iodate
IO4−
periodate
If the name of the anion in an acid
ends in “ide” just fill in the blank.
Acids have one, two, or three H+ ions written
first in the formula.
The rest of the formula is an anion.
When the name of the anion ends in “ide” the
name of the acid is:
Hydro______ic acid
Here the root of the anion fills in the blank.
If the anion contains oxygen, then
the ending changes.
If the anion in an acid contains oxygen change the
ending of the polyatomic ion:
“ate” to “ic”
“ite” to “ous”
Then say the name of the polyatomic ion with the
changed ending followed by “acid”