
Atoms are the
smallest
quantities of
matter that still
retain the
property of that
matter


Democritus was the first to develop this idea
of an atom in the 5th century
John Dalton was the first to formalize the
idea of an atom with Dalton’s atomic theory
 Known as the “father of atomic theory”

The word “atom” comes from the Greek word
“atomos” meaning “uncuttable.”





All matter is made up of atoms
Atoms are indivisible
Atoms of the same element are identical
Atoms of one element are different than
atoms of another element
Atoms come together to form compounds

If two elements can combine to create
multiple compounds, then the ratios of the
masses of the second element which
combine with a fixed mass of the first
element will be ratios of small whole numbers

CO
100 g of C
133 g of O


CO2
100 g of C
266 g of O
Discovery
Who Discovered It
How was it
Discovered
Electron (and
Charge-to-Mass
ratio)
Charge of the
Electron
Proton & Nucleus
J.J. Thomson
Cathode Ray Tube
(Cathode Ray
Experiment)
Oil Drop
Experiment
Gold Foil
Experiment
Neutron
James Chadwick
Robert Millikan
Ernest Rutherford
Beryllium
Bombardment
Subatomic
Particle
Proton
Charge
Location
+1
Neutron
0
Electron
-1
In the
nucleus
In the
nucleus
Outside
nucleus
Contributio
n to Atom
Mass
Mass
Volume

Not all atoms of a given element are identical
 Most elements have 2 or more isotopes (atoms
with same # of protons, different # of neutrons)


Isotopes behave like each other
Named after their mass number
 Ex: U-235 (“Uranium two thirty five”)



If mass number is not given, use rounded atomic
mass from PT.
If mass number is given (or if protons & neutrons
are given), use that value instead of on the PT.
If mass # is different than what’s on PT, it is an
isotope

Atoms with charges (different # of electrons)
 Positive ions called cations
 Negative ions called anions
# of
Protons
14
# of
Neutrons
# of
Electrons
Mass
Number
14
18
20
14
13
Atomic
Number
10
29
6
Ion?
Isotope?

List the number of protons, neutrons, and
electrons in the following elements:
Carbon-14

Iodine-128
An atom has a mass number of 114 and 66
neutrons. Write the isotope notation for this atom.

Mass of an atom in atomic mass units (a.m.u)
 Based off of 1/12 of a carbon atom

Most elements are mix of isotopes in nature
 Average Atomic Mass is reported

The atomic masses of two stable isotopes of
copper, copper-63 and copper 65, are
62.929599 and 64.927793 amu, respectively.
If copper-63 is 69.17% and copper-65 is
30.83%, what is the average atomic mass of
copper?

The atomic masses of 34Cl and 35Cl are
34.0578 amu and 35.0147 amu, respectively.
Calculate the natural abundance of these two
isotopes. The average atomic mass of Cl is
35.45 amu.

Mostly metals (left of stair step)
 Good conductors of heat/electricity

Non metals (right of stair step)
 Poor conductors of heat/electricity

Metalloids/Semi-metals (on stair step)
 Properties of both metal and nonmetal
 B, Si, Ge, As, Sb, Te, Po, At

Groups: vertical columns
 Elements in the same group share similar
chemical properties
 18 groups

Periods: horizontal rows
 Elements transition from metal to nonmetal
across a period

A unit of quantity (how much)
 Mole = mol

1 mole = 6.022 x 1023 “particles”
 “particles” can be atoms, molecules, or formula
units
 This number is called Avogadro’s Number

Molar Mass = the mass of ONE MOLE of a
substance
 g/mol

1 mole of water = 18.02 grams

1 mole sodium chloride = 58.44 g

1 mole helium gas = 4.003 g

Molar mass is found by
 Listing elements in compound
 Determining their mass found on periodic table
 Multiplying by how many atoms there are
 Adding these values
 Ex: H2SO4

How many molecules of magnesium chloride
(MgCl2) are there in 67.35 grams of
magnesium chloride?

How many chlorine atoms are there in the
same mass of magnesium chloride?
1)Write the appropriate isotope notation for the
following: Z=29, A=64
+3
2)How many protons, neutrons, & electrons in
3)Rb-85(72.17%) is 84.911794. If the average atomic
mass of Rb is 85.4678, what is the atomic mass of
Rb-87(27.83%).
4)How many grams is 5.30 x 1023 molecules of K2O?