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Physical Science
Parts of the Atom & The Periodic Table
History of the Atom
Democritus – first person to think of what
matter is made of around 400 BC. Theory
was that matter was made up of substances.
 Aristotle – disputed Democritus and came up
with his own theory that matter was uniform
throughout and NOT made of smaller
particles. Theory was accepted for 2000
years!!! UNTIL…
 John Dalton – proved that smaller “atoms”
existed proving Democritus right and Aristotle
wrong.
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Changes in the Atomic Model
Assignment
Read p. 548
 Sketch the five types atomic models and
label each with the year and the name and
discoverer.
 Place these sketches on white paper and
put in the basket.
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Parts of the Atom
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Protons (p+)
Electrons (e-)
Neutrons (no)
History of the Periodic Table
The periodic table was discovered by
Dmitri Mendeleev in the late 1800s.
He arranged the elements in order by
their atomic masses. The first periodic
table was written on paper!! p.554
In 1913, Henry Moseley
rearranged the periodic table by
their atomic numbers instead of
the atomic masses. p.555
Periodic Table
Atomic # = electrons
and protons
 Mass # = protons
plus neutrons
(average atomic
mass)
 Isotopes - atoms with
the same number of
protons but different
number of neutrons
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Practice Sheet
Half – Life
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1.
2.
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Def: the time it takes for half of the
radioactive atoms to change into another
element due to a change in protons
p. 552: Problem-Solving Activity
Look at the table.
How long does it take uranium-238 to turn
to lead-206?
How long would it take for 75% to change?
Solutions: 1. 4,460 years 2. 3,345 years
Families on the Periodic Table
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Group 1 = Alkali Metals
Group 2 = Alkaline Earth Metals
Group 3-12 = Transition Metals
Metalloids
Bottom groups= Inner Transition Metals
Group 13 = Boron Group
Group 14 = Carbon Group
Group 15 = Nitrogen Group
Group 16 = Oxygen Group
Group 17 = Halogens
Group 18 = Noble Gases
Masses of Atoms
mass of protons and neutrons are about
the same
 mass of an electron is very, very close to
zero (like a cloud)
 # of neutrons = mass # - atomic #
 average atomic mass – the weighted
average mass of the mixture of isotopes
(like grades done by %)

Electron Energy Levels
There are a possible 7 energy levels for the
periodic table.
 There are enough known elements to occupy
only 4 of these energy levels.
level 1 = 2 elevel 2 = 8 elevel 3 = 18 elevel 4 = 32 ep.558-559
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Electron Dot Diagrams
Valence electrons – outer energy level
electrons that can make chemical bonds
 Valence electrons are the ONLY electrons
used in dot diagrams.
 Once dot diagrams are made, then electrons
are paired to make compounds.
 Compounds are made by two ways:
Covalent bonding = sharing e- OR Ionic
bonding = transferring e- (taking them).
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Electron Dot Diagrams
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The Bohr model shows ALL electrons in their
orbitals or paths
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The Lewis Dot Diagram shows just the
valence electrons
Valence Electrons Across PT
Notice that
the transition
metals (3-12)
are skipped!!
Let’s Practice!!
How many valence electrons does
potassium have?
 How many valence electrons does bromine
have?
 How many valence electrons does xenon
have?
 How many valence electrons does
aluminum have?
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