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Atomic Model
Matter

Anything that has mass and volume
– Mass the amount of particles making up a
substance
– Volume is the amount of space taken up by
the particles

The basic unit of matter is the atom,
which is made up of protons, neutrons
and electrons
Proton
Positively charged (+)
 Located in the nucleus
 Mass number of 1
 Atomic Number = Number of Protons

– Atomic number on the periodic table
– Gives the identity of the atom
Neutron
No charge (neutral)
 Located in the nucleus
 Mass number of 1
 Mass of atom = protons + neutrons

– Must have a whole number of neutrons
– Average mass can be found on the
periodic table

Neutron number may be different to
form an isotope
Electron
Negatively charged (-)
 Constantly, randomly moving around
the nucleus in energy levels
 Mass number of 0
 If the atom is neutral (has a charge of
zero) then:

– Proton number = electron number

Electron number may change to form an
ion
– An atom with a + or - charge
Determining amount:

How many protons, neutron and
electrons are in an atom of Lead:
82
Atomic Number
Pb
Element Symbol
Lead
Element Name
207.2
Atomic Mass
Determining amount

How many protons, neutron and electrons are
in an atom of Lead:
 Number of protons = atomic number

– Atomic number = 82 = # of protons
Number of electrons = number of protons
– 82 = # of electrons

Atomic mass = protons + neutrons
207.2 = 82 + x
x = 125.2 must be a whole number
125 = number of neutrons
Try one on your own

How many protons, neutrons and
electrons are in an atom of silver:
47
Atomic Number
Ag
Element Symbol
Silver
Element Name
107.9
Atomic Mass
Model of atom
An atom can only be represented by a model since the
electrons are in constant random motion.
4th energy level _____ (can hold 8 electrons)
3rd energy level _____ (can hold 8 electrons)
2nd energy level _____ (can hold 8 electrons)
1st energy level _____ (can hold only 2 electrons)
Nucleus
Model: Atom of Sulfur (S)
Atomic number = 16
Determine total number of electrons
4th ____
3rd 6e2nd 8e1st 2eNucleus
Electrons
The number of electrons in the highest
energy level determines the behavior
and characteristics of the element
 Electrons in the highest energy level are
valence electrons
