Unit 6: Properties of
Matter
Ch 18: Atoms and Elements
Unit Six: Properties of Matter
 18.1
Atomic Structure
 18.2 Comparing Atoms
 18.3 The Periodic Table of
Elements
Chapter 18 Learning Goals
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Use indirect measurement to determine the radius of a
circle.
Build models of atoms.
Research one of the historical atomic models.
Understand how atoms of each element differ.
Describe the forces that hold an atom together.
Use the concept of electron shells to arrange electrons in
atomic models.
Understand how elements are organized in the periodic
table.
Use the periodic table to identify the atomic number and
mass numbers of each element.
Calculate the numbers of protons and neutrons in each
stable isotope of an element.
Chapter 18 Vocabulary Terms
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atomic mass
electrons

neutrons

nucleus
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periodic table of
elements
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atomic mass units
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atomic number
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atomic theory
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protons
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energy levels

strong nuclear force
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group of elements

subatomic particles
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isotopes
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valence electrons
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mass number
I. Atomic Structure
A. What are atoms?
1. atoms are building block of
molecules
a. Every element is made of tiny, unique
particles called atoms that cannot be
subdivided stably
b. Atoms of the same element are exactly
alike
c. Atoms of different elements can join to
form molecules
d. An atom is the smallest part of an
element that still has the properties of
the element
B. Make-up of the Atom
1. nucleus
a. the center of an atom
b. made up of protons and neutrons
2. proton
a. a positively charged subatomic
particle in the nucleus of an atom
3. Neutron
a. a neutral subatomic particle in the
nucleus of an atom
4. Electron
a. a tiny negatively charged subatomic
particle moving around the nucleus
C. Atoms have no overall charge
1. atoms have the same number of
protons (+) and electrons (-)
2. ie - Helium
protons
2
2+
neutrons
2
0
electrons
2
2TOTAL CHARGE 0
The symbols for
some elements
don’t always
obviously match
their names.
II. Comparing Atoms
A. atomic number
1. the number of protons in the
nucleus
2. also the number of electrons in a
neutral atom
B. mass number
1. the total number of protons and
neutrons in the nucleus
C. Calculating the number of neutrons
mass number
- atomic number
number of neutrons
D. Isotopes
1. any atoms having the same number
of protons, but different numbers of
neutrons
Isotopes of Hydrogen
E. Mass of an atom
1. atomic mass
a. the weighted average of all the
masses of all naturally occurring
isotopes of an element
18.1 Changing model of the
atom
John Dalton's Atomic Theory 1808
1.
2.
3.
4.
5.
Each element is composed of extremely small
particles called atoms.
All atoms of a given element are identical.
Atoms of different elements have different
properties, including mass and chemical
reactivity.
Atoms are not changed by chemical reactions,
but merely rearranged into different
compounds.
Compounds are formed when atoms of more
18.1 Changing model of the
atom

The Thompson model
suggested negative
electrons were
embedded in a
positive sphere.
18.1 Changing model of the
atom

Bohr's model
showed electrons
moving around the
nucleus in fixed
orbits.
18.1 Changing model of the
atom

Schrödinger's
mathematical model
demonstrated that the
electron position could
be predicted, but not
pinpointed exactly.
18.1 Changing model of the
atom

Dalton pictured the
atom as a small
hard sphere.
18.1 Atomic Structure
Key Question:
How was the size of an
atom's nucleus
discovered ?
F. Electron Arrangement
1. electron cloud
a. the area outside the nucleus
where electrons are found
2. energy level
a. a region around the nucleus of an
atom where electrons are most likely
to be found (within the cloud)
b. electrons move so fast that it is
almost impossible to determine their
exact location at any given moment
c. Number of Electrons in Energy Levels
1) energy level 1 – 2 electrons
2) energy level 2 – 8 electrons
3) energy level 3 – 18 electrons
4) energy level 4 – 32 electrons
d. Electrons are found in orbitals within
energy levels
1) s orbital
a) sphere shaped
b) closest to the nucleus
c) holds 2 electrons
2) p orbital
a) dumbbell-shaped
b) 3 different orientations each
holding 2 electrons – total 6 electrons
3) d orbital
a) 5 different orientations
b) each can hold 2 electrons
c) total 10 electrons
4) f orbital
a) 7 different orientations
b) each can hold 2 electrons
c) total 14 electrons
5) s orbital has the lowest energy and f
orbital has the highest energy level
6) Electrons will be found in the lowest
energy level and then fill higher levels
18.3 The Periodic Table of
Elements
Key Question: What does atomic
structure have to do with the periodic
table?
II. The Periodic Table of the Elements
A. Periodic Law
1. properties of elements tend to
change in a regular pattern when
elements are arranged in order of
increasing atomic number, or number
of protons in their nucleus
B. Period
1. a horizontal row of elements in the
periodic table
2. the number of protons increases by
one from left to right
3. the number of electrons increases
by one from left to right
4. the row number indicates how many
energy levels are present
C. Group
1. a vertical column of elements in the
periodic table
2. elements in the same group have
similar properties
3. valence electrons
a. an electron in the outermost
energy level of an atom
b. determines the atom’s chemical
properties
IV. Families of Elements
A. Classifying Elements
1. metals
a. the elements that are good
conductors of heat and electricity
2. nonmetals
a. the elements that are poor
conductors of heat and electricity
3. semiconductors/metalloids
a. the elements that are intermediate
conductors of heat and electricity
B. Metals
1. alkali metals
a. the highly reactive metallic
elements located in Group 1 of the
periodic table
b. one valence electron – highly
reactive
c. Bond with other elements to form
compounds
2. alkaline-earth metal
a. the reactive metallic elements
located in Group 2
b. 2 valence electrons – thus they react
with other elements
3. Transition metals
a. the metallic elements located in
Groups 3-12
b. less reactive than the alkali and
alkaline-earth metals
c. valence electron number varies
1) 2-5 ?
4. Synthetic elements
a. all elements with atomic numbers
greater than 92
b. found at bottom of periodic table
C. Non-Metals
1. on the right side of periodic table
plus hydrogen
2. carbon is found in three different
forms and can also form many
compounds
3. nonmetals and their compounds are
plentiful on Earth
4. Halogens
a. the highly reactive elements located
in Group 17
b. 7 valence electrons
5. Noble gases
a. the non-reactive gaseous elements
in Group 18
b. 8 valence electrons
6. semiconductors/metalloids
a. classified as nonmetals
b. have some properties of metals
c. conduct heat and electricity
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