2.2 REVIEW
1. Atomic Number, Mass Number, Atomic Symbol
Atomic number, Z, is the number of protons
An atomic symbol represents the element
The mass number is equal to protons +neutrons
2.3 ISOTOPES
Definition: Two or more forms of the same element
containing different numbers of neutrons. Isotopes
of an element have the same chemical properties but
differing mass numbers.
Examples:
3. Mass Spectrometer and percent abundance
A device that measures both the individual mass
numbers and the percentages of each isotope that
exist in a sample of an element.
The percentage an isotope makes up of the entire isotope
that exists in nature.
2.4 ATOMIC WEIGHT
1. Atomic mass or Atomic weight
one amu (atomic mass unit) = exactly 1/12 of the
mass of a carbon-12 atom
Atomic weight (mass) is the weighted average of the
masses of an elements’ isotopes
*in chemistry the terms atomic weight and atomic mass
are used interchangeably
EX2.1
Boron exists in two naturally, occurring isotopes. B-10 ( 10.016 amu) makes
up 18.83% of each natural sample of this element. The remaining
81.17% of the sample is B-11 (11.013 amu). What atomic mass would
be calculated for this mixture of isotopes?
Solve by multiplying isotope mass by %
Boron -10
(10.016) (0.1883)
= 1.8860
Boron -11
(11.013) (0.8117)
= +8.9393
10.825 amu
Keep 5 sig figs – consider percent as exact number 
EX2.2
The two natural isotopes of Lithium are 6Li (6.01512 amu) which accounts
for 7.42% of the total and 7Li which accounts for the remaining amount.
If the mass of lithium is shown as 6.942 on the periodic table, what is
the mass of the Li -7 isotope? (answer = 7.016 amu)
4. MOST ABUNDANT NATURAL ISOTOPE
Hydrogen is the most abundant natural isotope
2.5 ATOMS AND THE MOLE
1. Definition: the amount of a substance that contains
as many “representative particles” ( atoms,
molecules, or other particles) as there are atoms in
12grams of carbon-12 atoms.
1 mole = 6.022045 x 1023 r.p.’s
ANALOGY
Bakery count
1 dozen = 12 donuts
Chemists use moles like dozens to make things more
manageable
http://www.youtube.com/watch?v=g_BelGwRxG8
3. Avogadro’s Number
1 mole = 6.022 x 1023 particles
4. Second Definition
The mass of 1 mole of atoms of a pure
element in grams is equal to the atomic mass
of that element in amu
EX 2.3
One mole of sulfur contains 6.022 x 10 23 atoms of sulfur and has a
mass of 32.06 grams. What is the mass of one atom of sulfur? (Use
32.1 to determine sig. figs.) (answer = 5.33x10-23 g)
EX 2.4
How many sulfur atoms are present in 1.00 grams of sulfur?
(answer = 1.88x1022 atoms S)
EQUIVALENCIES AND CONVERSION FACTORS
Formula
H
H2 =
H2O =
H2SO4 =
Formula mass (amu)
1.00794 amu
g/mole
g/mole
g/mole
Molar Mass (g)
1.00794 g/mole
SAMPLE MOLE PROBLEMS
Ex2.5 How many moles are equivalent to 5.00 g CaCO3?
(Add molar masses of calcium, oxygen and carbon present to get the
molar mass)
5.00 grams CaCO3 1 mole CaCO3
= 0.0500 moles CaCO3
100.1 g CaCO3
Ex2.6 A microchemical experiment requires 0.0100 moles
of Al(NO3)3. How many grams is this? (answer = 2.13 g)
MORE MOLE PROBLEMS
Ex. 2.7 For exactly 1.000 g of carbon disulfide (CS 2), how many molecules are
present? How many atoms of sulfur?
1.000 g CS2 1 mole CS2 6.022 x 1023 molecules CS2 = 7.903 x1021 molc. CS2
76.2 g CS2
1 mole CS2
7.903 x1021 molc. CS2
Ex2.8 A sample of sulfur hexafluoride (SF6) contains 1.69 x 1022 atoms of fluorine.
What is the mass of the sample? (answer = 2.48x1047 g SF6)
THE PERIODIC TABLE
1. History
Mendeleev, 1869 developed the first periodic table by identifying
similarities among the elements; based on increasing
atomic mass
Periodic Law – The properties of elements repeat when
arranged by atomic number (updated after Moseley’s
work)
Moseley, 1913 - organized the P.T. by atomic number
THE PERIODIC TABLE
Groups or families – columns down the P.T.
Periods or series – rows across P.T.
Metals - on the left side of the staircase , metalloids - along
the staircase, nonmetals - on the right side of the
staircase
Main group elements – the “A” groups of P.T.
Transition metals – in the middle
Lanthanides and Actinides – bottom double rows
Specific Family Names to Memorize:
Specific Family Names to memorize:
Group 1 – Alkali metals
Group 2 – Alkaline Earth metals
Group 17 (7A) – Halogens
Group 18 (8A) – Noble gases
PERIODIC TABLE
http://www.youtube.com/watch?v=SmwlzwGMMwc
Coulomb’s Law – a helpful tool in explaining P.T. trends
• Page 93 of the textbook
The magnitude of the electrostatic force of interaction
between two point charges is directly proportional to the
product of the charges and inversely proportional to the
square of the distances between them.
Two charges of the same sign=repulsive force; Two
charges of opposite sign=attractive force; At least one is
neutral=no force
• Like charges repel
• opposite charges attract
Coulomb’s Law
•
video
The Equation
q1q2
F  ke 2
d
where F is force ( Newtons ) , q1and q2 represent charge (Coulomb's),
d is distance ( meters ) between electrons, and ke is Coulomb's constant
Applying Coulomb’s Law to P.T.
• Throughout our study this year, we will apply
Coulomb’s Law to support observed properties
such as melting point and boiling point
• The product of the charges and the force of
attraction is directly proportional
• The square of the distances and the force of
attraction is inversely proportional
HOMEWORK CHAPTER 2
HW#1 -21, 23, 25, 27, 29, 47 Composition Atoms, Isotopes
HW#2 - 31, 33, 35 Atomic Symbols Wkst
HW #3 – 37, 39, 59, 61, 62, 63
HW #4 - Mole Relationships Wkst.
HW #5 - 43, 45, 57 PT