 Mass Number
 Isotopes
 Ion




Elements on the
periodic table are
made of atoms.
Atoms are the smallest
form of matter.
All atoms in an
element look the
same.
The structure of an
atom determines how
that atom will react
with other atoms of a
different element
Atom:
Element:
8
O
15.99999






Proton = p+
Electron = eNeutron = n0
Atomic # is the number
at the top of each
block on the periodic
table
Atomic # = #p
Neutral Atom #p = #e-
1
H
1.00784
Mass # = protons + neutrons
 always a whole
number
 NOT on the
Periodic Table!
© Addison-Wesley Publishing Company, Inc.
Each
element has billions
of atoms so it is important
to name each one
correctly.
Naming a single atom is
called atom notation
1. Nuclear Symbol: Mass #atomic #symbol
2. Hyphen Notation: element name – mass #
 Hyphen notation: carbon-12
 Nuclear symbol:
Mass #
Atomic #
12
6
C
REMEMEBER!!!
 # p = atomic #
 Mass # = #p + #n
Hyphen Notation:
Oxygen – 16
Nuclear Symbol:
16
8
O
 Chlorine-37
› atomic #:
17
› mass #:
37
› # of protons:
17
› # of electrons: 17
› # of neutrons:
20
37
17
Cl
Remember:
Neutral = same number of (+) and (-)

Neutral Atom = same number of p+ and e-
Atoms are not always neutral. Sometimes emove around – this causes and atom to
become an ion.
 An
atom with an unequal amount of
p+ and e- causes a charge to form
 Loses
e- (More protons) = (+) charge
 Gains
e- (More electrons) = (-) charge
 The
quantity of the electrons lost or
gained determines the charge quantity
Ion
Neutral
atom
Ion
Neutral
atom
An ion can only be named using the
nuclear symbol or if the picture is given.
 Nuclear Symbol:

19
9

F
-1
You cannot identify an ion or name an
ion by hyphen notation.

Oxygen - 16
› atomic #:
8
› mass #:
16
› # of protons:
8
› # of electrons:
10
› # of neutrons:
8
16
8
-2
O

Remember: an
element is made of
billions of tiny atoms.
(602,000,000,000,000,000,000,000)
Atoms all look alike
(same #p)
 Atoms do not weigh
alike (different mass#)

Atom:
Element:
12
12
148
12
12
12
12
12
12
14
8
12
Carbon – 12
Carbon – 14
© Addison-Wesley Publishing Company, Inc.

All elements have isotopes meaning all
elements are made of tiny atoms that
have different masses.