The Atom
Atomic Number and Mass
Number
Isotopes
1
Atomic Theory
 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
Subatomic Particles
Particle
Symbol
Charge
Relative
Mass
Electron
e-
1-
0
Proton
p+
+
1
Neutron
n
0
1
3
Location of Subatomic Particles
electrons (-)
protons (+)
nucleus
neutrons (0)
4
Atomic Number
Counts the number
of
protons
in an atom
5
Periodic Table
 Represents physical and chemical
behavior of elements
 Arranges elements by increasing atomic
number
 Repeats similar properties in columns
known as chemical families or groups
6
Periodic Table
1
2
3
4
5
6
7
8
11
Na
7
Atomic Number on the
Periodic Table
Atomic Number
Symbol
11
Na
8
All atoms of an element have
the same number of protons
11 protons
Sodium
11
Na
9
Learning Check AT 1
State the number of protons for atoms of
each of the following:
A. Nitrogen
1) 5 protons
2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons
2) 16 protons
3) 6 protons
C. Barium
1) 137 protons 2) 81 protons
LecturePLUS Timberlake
3) 56 protons
10
Solution AT 1
State the number of protons for atoms of each
of the following:
A. Nitrogen
2) 7 protons
B. Sulfur
2) 16 protons
C. Barium
3) 56 protons
LecturePLUS Timberlake
11
Number of Electrons
 An atom is neutral
 The net charge is zero
 Number of protons = Number of electrons
 Atomic number = Number of electrons
A=P=E
Atomic# = #p+ = #e-
12
Mass Number
Counts the number
of
protons and neutrons
in an atom
M–A=N
Mass# - Atomic # = # n(0)
13
Atomic Symbols
 Show the mass number and atomic number
 Give the symbol of the element
mass number
23 Na
atomic number
sodium-23
11
14
More Atomic Symbols
16
O
31
P
65
8
15
30
15 p+
16 n
15
e
LecturePLUS Timberlake
30 p+
35 n
30 e-
8 p+
8n
8 e-
Zn
15
Isotopes
 Atoms with the same number of protons,
but different numbers of neutrons.
 Atoms of the same element (same atomic
number) with different mass numbers
Isotopes of chlorine
35Cl
37Cl
17
17
chlorine - 35
chlorine - 37
16
Learning Check AT 2
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
13C
14C
6
6
6
#P _______
_______
_______
#N _______
_______
_______
#E _______
_______
_______
17
Solution AT 2
12C
6
13C
14C
6
6
#P __6___
_ 6___
___6___
#N __6___
_ _7___
___8___
#E __6___
_ 6___
___6___
18
Learning Check AT 3
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
2) 35
3) 65
B. Number of neutrons in the zinc atom
1) 30
2) 35
3) 65
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) 37
2) 65
LecturePLUS Timberlake
3) 67
19
Solution AT 3
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
B. Number of neutrons in the zinc atom
2) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
3) 67
20
Learning Check AT 4
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-
___________
LecturePLUS Timberlake
21
Solution AT 4
16O
A. 8 p+, 8 n, 8 eB. 17p+, 20n, 17e-
8
37Cl
17
C. 47p+, 60 n, 47 e-
107Ag
47
LecturePLUS Timberlake
22
Learning Check AT 5
An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) 14
2) 16
3) 34
B. Its mass number is
1) 14
2) 16
3) 34
C. The element is
1) Si
2) Ca
3) Se
D. Another isotope of this element is
1)
34X
16
2)
34X
14
LecturePLUS Timberlake
3)
36X
14
23
Solution AT 5
An atom has 14 protons and 20 neutrons.
A. It has atomic number
1) 14
B. It has a mass number of
3) 34
C. The element is
1) Si
D. Another isotope of this element would be
3) 36X
14
LecturePLUS Timberlake
24
Masses of Atoms
 A scale designed for atoms gives their small
atomic masses in atomic mass units (amu)
 An atom of 12C was assigned an exact mass of
12.00 amu
 Relative masses of all other atoms was
determined by comparing each to the mass of
12C
 An atom twice as heavy has a mass of 24.00
amu. An atom half as heavy is 6.00 amu. 25
Atomic Mass
Na
22.99
 Listed on the periodic table
 Gives the mass of “average” atom of each
element compared to 12C
 Average atom based on all the isotopes and their
abundance %
 Atomic mass is not a whole number
LecturePLUS Timberlake
26
Learning Check AT6
Using the periodic table, specify the
atomic mass of each element (round to the
tenths place):
A. calcium
__________
B. aluminum
__________
C. lead
__________
D. barium
__________
E. iron
__________
27
Solution AT6
Using the periodic table, specify the
atomic mass of each element (round to the
tenths place):
A. calcium
_40.1 amu _
B. aluminum
_27.0 amu _
C. lead
_207.2 amu_
D. barium
_137.3 amu_
E. iron
_55.8 amu__
28