ATOMS AND THE
PERIODIC TABLE
CHAPTER 4
Meet the Elements
VOCABULARY --REVIEW and
INTRODUCTION
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Atoms – smallest part of an element that still
retains all properties of that element.
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Atoms can be broken down into subatomic
particles.
Atoms can combine to form molecules.
Molecule – the smallest part of a compound
that still retains all properties of that
compound.
ELEMENTS, ATOMS, MOLECULES,
COMPOUNDS
Subatomic
Particles
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Nucleus – center of atom
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Neutrons – no charge
Protons – positive charge
Energy Levels – located around nucleus
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Electrons – negative charge
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Electrons move in a cloud around the nucleus
Atomic Models
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Bohr’s Model (1913)
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Niels Bohr suggested electrons moved in orbits
around the nucleus … similar to planets moving
around the sun.
Each electron could only move in specific orbits or
paths.
Atomic Models
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1925 – Electron Cloud Model
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Electrons move in a region or general area
surrounding the nucleus. (called an electron cloud)
An electrons exact speed, direction or location
cannot be determined at any one particular moment.
Electrons are located at various distances around
the nucleus
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Electrons close to the nucleus have LOW energy
Electrons far away from the nucleus have HIGH energy
Electron Cloud
Model
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Electrons exist in energy levels
The number of energy levels that are filled will
depend on the number of electrons of that
atom.
1st energy level holds 2 electrons
2nd energy level – 8 electrons
3rd energy level – 18 electrons
4th energy level – 32 electrons
Electron Cloud Model
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Octet Rule – An atom is considered stable
(happy) when its outer energy level is full of
electrons. (8 outer electrons is considered stable).
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Valence Electrons – Electrons found in the
outermost shell of an atom
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Valence Electrons determine the chemical properties of
an atom.
When valence shell is not full…the atom will be more
reactive
Dot Diagrams (Lewis Structure) and
Valence Electrons
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Uses the symbol of the element and dots to
represent the electron in the outer energy level
Periodic Table
Element Song
Dmitri Mendeleev: Father of the
Periodic Table
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HOW HIS WORKED…
Put elements in rows by
increasing atomic
weight.
Put elements in
columns by the way
they reacted.
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SOME PROBLEMS…
He left blank spaces for
what he said were
undiscovered elements.
(Turned out he was
right!)
He broke the pattern of
increasing atomic
weight to keep similar
reacting elements
together.
The Current Periodic Table
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Mendeleev wasn’t too far off.
Now the elements are put in rows by
increasing
ATOMIC NUMBER!!
Periodic Table
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The arrangement of elements according to
repeating changes in properties
Each box on the periodic chart contain the
atomic number, chemical symbol, name, and
average atomic mass.
Periodic Table Organization
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Groups – A vertical Column of
elements
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Elements in the same group have
the same number of valence
electrons.
Elements of the same group have
similar chemical properties.
Periods – Horizontal Rows
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The number of protons increase
by one from left to right (so do #
of electrons)
Periodic Table
Organization
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Chemical Symbol – Abbreviated way to write the
name of the element (EX: O – Oxygen)
Atomic Number – The number of protons in the
nucleus
Atomic Mass Number – The number of protons plus
neutrons in the nucleus (often a decimal number)
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This number may be rounded…round up if it is .5 or
above and down if .4 or below)
The mass number is an AVERAGE
Ions and Isotopes
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Ions – An atom or group of atoms that has lost
or gained one or more electrons and has a
negative or positive charge
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Occurs when an atom gives up an electron or takes
an electron because outer energy levels are not full
CATION – positive ion (loses electrons and
becomes positive)
ANION – negative ion (gains electrons and
becomes negative)
(pictures)
Ions and Isotopes
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Isotopes – An atom that has the same number
of protons as other atoms of the same element
do but has a different number of neutrons.
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Isotopes are often radioactive
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Used for cancer treatments, preserving foods, etc.
Example: Hydrogen has three isotopes
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Protium, Deuterium, Tritium
Isotopes of
Hydrogen and Carbon
Families of Elements
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Members of a family in the periodic table have
many chemical and physical properties in
common…they have similar valence electrons.
3 Groups:
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Metals, Nonmetals, Semiconductors
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The Periodic Table of Videos - University of
Nottingham
Hydrogen
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Hydrogen belongs to a family of
its own.
Hydrogen is a diatomic, reactive
gas.
Hydrogen was involved in the
explosion of the Hindenberg.
Hydrogen is promising as an
alternative fuel source for
automobiles
Metals
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Four different kinds
of metals
Share common
properties of:
existing as solids at
room temperature,
shiny, good
conductors of heat
and electricity
1. Alkali Metals
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Group 1
Very Reactive…Have only 1 valence electron
Always combined with something else in
nature.
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Example: Sodium must be stored in oil so as not to
react with moisture in air.
2. Alkaline-Earth Metals
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Located in Group 2
Have 2 valence electrons
Less reactive than Alkali Metals
Always combined with nonmetals in nature
Ex: Calcium and Magnesium
3. Transitional
Metals
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Groups 3-12
Much less reactive
These elements properties gradually change
from being more similar to Group 2 to being
more similar to Group 13 as you move from left
to right
Examples: Gold, Platinum, Silver
4. Synthetic Elements
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All elements above #92 are man-made
Many are radioactive
Nonmetals
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Located on the right side of the periodic table
Includes some elements in Groups 13-16 and
all elements in Groups 17-18
Plentiful on Earth
3 Groups
1. Halogens
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Group 17
Very Reactive
Always combined with another element in
nature
Has 7 valence electrons
Used as disinfectants and to strengthen teeth
2. Noble Gases
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Group 18
Unreactive; Do not
make compounds with
anything.
8 Valence Electrons
(full outer energy level)
3. Semiconductors (Metalloids)
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Intermediate conductors of heat and electricity
Includes 6 elements
Located on the “stairstep line”
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Includes: Boron, Silicon, Germanium, Arsenic,
Antimony, Tellurium
Diatomic
Molecules
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If these elements are found alone in nature
they are always bonded to themselves
because they are very reactive.
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Example: O2, H2, Fl2, Br2, I2, N2, Cl2
There are 7
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Including: Hydrogen, Oxygen, Fluorine, Bromine,
Iodine, Nitrogen, Chlorine