Chapter 5 – Atomic Structure
 Atoms
 Structure of An Atom
 Distinguish Between
Atoms
 The Periodic Table
Ch 5.1 Atoms
 Democritus of
Abdera (Greece)
 4th Century BC
 Coined the term
“atom”
 Could not prove
because no
scientific research
was being done
John Dalton (1766-1844)
 Conducted research
as to the ratios of
elements in
compounds
 From the research
he came up with
Daltons Atomic
Theory
Dalton’s Atomic Theory
 1. All elements are
composed of tiny
indivisible particles
called atoms.
Dalton’s Atomic Theory
 2. Atoms of the
same element are
identical. The atoms
of one element are
different from those
of any other
element.
Dalton’s Atomic Theory
 3. Atoms of different elements can physically
mix together or can chemically combine with
one another in simple whole number ratios to
form compounds.
Dalton’s Atomic Theory
 4. Chemical reactions
occur when atoms are
separated, joined or
rearranged. Atoms of one
element, however, are
never changed into atoms
of another element as a
result of a chemical
reaction.
Atom
 The smallest particle
of an element that
retains the
properties of that
element.
Just How Small is an Atom
 A pure copper coin about the size of a penny
has 2.4 x 1022 atoms
 2,400,000,000,000,000,000,000,000 atoms
 Earths population is only 6 x 109 people
Just How Small is an Atom
 A 1cm long line of
copper atoms has
100,000,000 atoms
Ch 5.2 Structure of the
Nuclear Atom
 Particle Accelerators
are used to smash
particles at speeds near
the speed of light into
each other in order to
break them apart
 A bubble chamber is
used to track the paths
of the broken particles
 Cant ever see the
actual particles
Electrons
 Negatively charged
subatomic particle
 e-
Electrons
 J.J. Thomson (1856-
1940) discovered
electrons in 1897
 Invented cathode ray
tubes (used in TVs)
Electrons
 Robert Millikan
(1868 – 1953)
 Determined an
accurate mass of an
electron
 Mass 1/1840 of a
hydrogen atom
Protons
 E. Goldstein (1886)
discovered protons
in a cathode ray
tube
 Protons are
positively charged
 Mass is 1840 times
an electron
Neutrons
 James Chadwick
(1932) discovered
neutrons
 No Charge
 Mass the same as a
proton
Particle
Symbol Charge Relative Actual
Mass
Mass (g)
1/1840 9.11x10-28
Electron
e-
1-
Proton
p+
1+
1
1.67x10-24
Neutron
n0
0
1
1.67x10-24
Atomic Nucleus
 Rutherfords Gold Foil Experiment
 Shot rays of alpha particles at thin gold foil
 Most passed straight through
 Some bounced off at large angles
 Some bounced straight back
 Suggested that an atom is mostly empty
space with most of the mass and the positive
charge in the center (nucleus)
Ch 5.3 Distinguish Between
Atoms
 Atoms are made up
of

Electrons
 Protons
 Neutrons
 Nucleus contains
protons and
neutrons
Atomic Number
 The number of
protons in the
nucleus of an
element
 Every element has a
different atomic
number
Atomic Number
 The number of
protons equals the
number of electrons
 Protons are positive,
electrons are
negative, therefore
the total net charge
of an atom is 0
Mass Number
 The number of
protons and
neutrons.
 Number of neutrons
equals mass
number minus
atomic number
Mass Number
 The number of
protons does not
always equal the
number of neutrons
 Oxygen
 Beryllium
Isotopes
 There are different
types of neon
 What is different?
Isotopes
 All of the neon's
have the same
number of protons
and electrons, but
different number of
neutrons
 Ne-20 has 10
 Ne-21 has 11
 Ne-22 has 12
Isotopes
 Atoms that have the
same number of
protons and
electrons but
different numbers of
NEUTRONS.
 This also creates a
different mass
number for each.
Hydrogen
Atomic Mass
 AMU (Atomic Mass
Units) defined as
1/12 the mass of
carbon-12 or 1 amu.
Atomic Mass
 The weighted
average mass of the
atoms in a naturally
occurring sample of
the element.
 Based on the
percent of each
isotope present on
earth.
Atomic Mass
 Chlorine 35 – 75.77%
 Chlorine 37 – 24.23 %
 Average Mass based
on Percents = 35.453