 Smallest
part of an element
with all the properties of that
element.
 2 parts
Center of
atom
 most of
atomic mass
 contains
protons &
neutrons

Nucleus

5
B



Mass # = Mass of
the nucleus
1 proton = 1amu
(atomic mass unit)
1 neutron = 1 amu
The average #
protons + #
neutrons
Electrons too small
to contribute to mass
Boron

10.81
Mass
11
24
36
Na
Cr
Kr
Sodium
22.99
Chromium
51.99
Krypton
83.80
A. 11
A. 24
A. 36
B. 23
Na = 23
C. 22.99
B. 51
Cr = 52
C. 51.99
B. 83
Kr = 84
C. 83.80
D. 22
D. 52
D. 84




Cloud of electrons
that surrounds the
nucleus
Individual electrons
move so fast, they
appear as a cloud
Most of the volume of the
atom.
Mostly empty space.
-
-
Electron Cloud
1.
2.
3.
Protons: positive charge (+)
located in nucleus
Neutrons: neutral charge (=)
located in nucleus
Electrons: negative charge (-)
located in the electron cloud


# protons (positive charges) = atomic #
Atoms of different elements have different
numbers of protons.
Atomic
Number
5
B
Boron
-
= +
+ = =
= + =
+ = +
-
10.81
-
11
24
36
Na
Cr
Kr
Sodium
22.99
A. 11
Chromium
51.99
A. 24
Krypton
83.80
A. 36
B. 23Na = 11+
Cr = 24+
B. 51
Kr = 36+
B. 83
C. 22.99
C. 51.99
C. 83.80
D. 22
D. 52
D. 84



Which atom has 8 protons?
Which atom has 6 protons?
Which atom has 7 protons?
A. Carbon B. Nitrogen
C. Oxygen D. Moccium
Oxygen
Carbon
Nitrogen
6
7
8
C
N
O
Carbon
12.01
Nitrogen
14.00
Oxygen
15.99

# neutrons (neutral, no charge) =
mass – protons (atomic #)
Atomic
Number
(#
protons)
5
-
B
Boron
Mass
(#
protons + #
neutrons
-
10.81
-
= +
+ = =
= + =
+ = +
-
-
11 (rounded)
-5
6 neutrons
11
24
36
Na
Cr
Kr
Sodium
22.99
A. 11
Na
B. 12 23
-11
C. 22.99
12 =
D. 22
Chromium
51.99
A. 24
Cr
B. 26 52
C. 28 -24
28 =
D. 52
Krypton
83.80
A. 36
Kr
B. 48 84
-36
C. 83.80
48 =
D. 84


# electrons (negative) = # protons (atomic #)
# negative charges = # positive charges, the
atom is neutrally charged (has no charge)
Atomic
Number
5
B
Boron
-
= +
+ = =
= + =
+ = +
-
10.81
-
11
24
36
Na
Cr
Kr
Sodium
22.99
A. 11
Chromium
51.99
A. 24
Krypton
83.80
A. 36
B. 23Na = 11-
Cr = 24B. 51
Kr = 36B. 83
C. 22.99
C. 51.99
C. 83.80
D. 22
D. 52
D. 84
1.
13
2.
Al
Aluminum
26.98
3.
How many protons (+) does an
atom of Aluminum have?
A. 13
B. 14
13 +
C. 26
D. 27
How many electrons (-) does an
atom of Aluminum have?
A. 13
B. 14
13 C. 26
D. 27
How many neutrons (=) does an
atom of Aluminum have?
27
A. 13
B.(mass
14 #)
-13 (atomic #)
C. 26
14D.= 27
1.
12
2.
Mg
Magnesium
24.31
3.
How many protons (+) does an
atom of Magnesium have?
A. 12
B. 13
12 +
C. 24
D. 25
How many electrons (-) does an
atom of Magnesium have?
A. 12
B. 13
12 C. 24
D. 25
How many neutrons (=) does an
atom of Magnesium have?
24B.(mass
A. 12
13 #)
-12 (atomic #)
C. 24
12D.
= 25
1.
15
2.
P
Phosphorus
30.97
3.
How many protons (+) does an
atom of Phosphorus have?
A. 15
B. 16
15 +
C. 30
D. 31
How many electrons (-) does an
atom of Phosphorus have?
A. 15
B. 16
15 C. 30
D. 31
How many neutrons (=) does an
atom of Phosphorus have?
31
A. 15
B.(mass
16 #)
-15 (atomic #)
C. 30
16D.= 31
How many
What
is the protons
atomic #(+),
of Neon,
and
neutrons
massand
of (=),
Fluorine,
how
and
many
electrons
and
protons
how(-)
does
(+)
many
and
an
electrons
neutrons
atom of(-)
Boron
(=)
does
does
have?
anan
atom
atom
of of
it have?
it have?
A. At#10,
5 (+), 5(=),
20(+),
mass
5(-)
19,
10(=)
10(-)B. 11(+),
B. At#19,
At#10,
11(=), mass
10(+),
11(-) 9,10(=)
9(-)
C. At#9,
5 (+), 6(=),
At#20,
mass
10(+),
5(-)
10,10(=)
9(-) D. 5(+),
D. 11(=),
At#10,mass
At#9,
5(-)
10(+),
19,20(=)
9(-)
Element Atomic #
Mass #
Protons Neutrons Electrons
+
=
-
Boron
5
11
5
Neon
10
20
10
Fluorine
9
19
9
6
5
10
10
10
9

# shells = # of ROW on Periodic Table
2 Energy
Levels
2nd Row
5
B
Boron
-
= +
+ = =
= + =
+ = +
-
10.81
-




1st Shell = No more than 2
2nd Shell = No more than 8
3rd Shell = No more than 8
Last Shell = # of COLUMN on Periodic Table
5 Electrons
5
B
Boron
-
= +
+ = =
= + =
+ = +
-
10.81
2 Electrons
in 1st shell
-
B is in 3rd Column
 3 electrons in
last shell





Teacher demonstrates diagramming atoms
with atomic #1, #2, #3, #10, #18
Students work with partners – one sheet of
paper per team.
Take turns diagramming the atoms. While one
draws, the other checks work.
One person diagrams the odd numbered
elements, partner checks work.
The other person diagrams the even numbered
elements, partner checks work.