 Atoms are building blocks of elements
 Similar atoms in each element
 Different from atoms of other elements
 Two or more different atoms bond in
simple ratios to form compounds
2
3
Particle Symbol Charge Relative
Mass
Electron e-
1-
0
p+
+
1
0
1
Proton
Neutron n
4

Atoms are composed of 2 regions:
Electron
Cloud
Nucleus
 Nucleus: the center of the
atom that contains the mass
of the atom
 Electron cloud: region that
surrounds the nucleus that
contains most of the space in
the atom
Number of protons in an
atom
All atoms of an element
have the same number of
protons
7
Atomic Number
Symbol
11
Na
8
11 Protons
Sodium
11
Na
9
State the number of protons for atoms of each of
the following:
Nitrogen
10
7 Protons
Nitrogen
7
N
11
State the number of protons for atoms of each of
the following:
Sulfur
12
16 Protons
Sulfur
16
S
13
State the number of protons for atoms of each of
the following:
Barium
14
56 Protons
Barium
56
Ba
15
Counts the number of
protons and neutrons in
an atom
Mass number=
+
p
+
0
n
16
Show the mass number and
atomic number
Give the symbol of the
element
17
Mass
number
23
11
Na
Atomic
number
18
What is the element?
Mass
number
35
17
Cl
How many protons?
How many neutrons?
Atomic
number
19
What is the element?
Mass
number
35
17
Cl
Chlorine
Atomic
number
20
Mass
number
35
17
Atomic
number
How many protons?
Cl p = atomic
# = 17
21
0
n
Mass
number
= 35 (mass number– 17
0
n
35
17
Cl
+
(p )
= 18
How many neutrons?
Atomic
number
22
An atom is neutral
The net charge is zero
Number of protons = Number of
electrons
Atomic number = Number of
electrons
23
=
8
n0 =
8
e- =
8
+
p
16
8
O
24
+
p
31
15
P
=
15
n0 =
16
e- =
15
25
=
30
n0 =
35
e- =
30
+
p
65
30
Zn
26
 Atoms with the same number of
protons, but different numbers of
neutrons.
 Atoms of the same element (same
atomic number) with different mass
numbers
27
Isotopes of chlorine
35Cl
17
chlorine - 35
37Cl
17
chlorine - 37
28
Naturally occurring carbon consists of three isotopes,
12C, 13C, and 14C. State the number of protons,
neutrons, and electrons in each of these carbon
atoms.
12C
6
13C
6
14C
6
#p _______
#n _______
_______
_______
_______
_______
#e _______
_______
_______
LecturePLUS Timberlake
29
12C
6
13C
6
6
14C
#p 6
6
6
#n 6
7
8
#e 6
6
6
LecturePLUS Timberlake
30
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
B. Number of neutrons in the zinc atom
C. What is the mass number of a zinc isotope
with 37 neutrons? Draw its atomic symbol.
31
An atom of zinc has a mass number of 65.
A.Number of protons in the zinc atom
30
32
An atom of zinc has a mass number of 65.
B. Number of neutrons in the zinc atom
35
33
C. What is the mass number of a zinc isotope
with 37 neutrons? Draw its atomic symbol.
67
67
30
Zn
34
Write the atomic symbols for atoms with
the following:
A. 8 p+, 8 n, 8 e___________
B. 17p+, 20n, 17e-
___________
C. 47p+, 60 n, 47 e-
___________
35
A. 8 p+, 8 n, 8 e-
16O
8
B.17p+, 20n, 17e-
37Cl
17
C. 47p+, 60 n, 47 e-
107Ag
47
36
Atomic Number
Symbol
Atomic Mass
11
Na
22.99
37

Atomic mass is the
weighted average mass
of all the atomic masses
of the isotopes of that
atom.
38
Ion – charged particle
that forms when an
atom gains or loses
one or more electrons
Cation – positively
charged particle when
an atom loses electrons
protons(+) > electrons(-1)
+2
Ca
protons(+) = 20
electrons(-) = 18
Anion – negatively
charged particle when
an atom gains electrons
electrons(-) > protons(+)
-3
N
protons(+) = 7
electrons(-) = 10