Transcript Atoms & Isotopes - La Salle High School

The Atom
Atomic Number and Mass
Number
Isotopes
Three fundamental parts of an atom are:
protons
electrons
neutrons
Structure of the atom is:
protons and neutrons are found in the nucleus
electrons are located outside of the nucleus
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
Subatomic Particles
There are three subatomic particles that are of
interest to chemists. These particles define the
nature of atoms and how they are put together.
These particles are:
• Neutrons
• Protons
• Electrons
Properties of Subatomic Particles
Relative
mass to
C-12, amu
Charge,
Coulombs
Unit
Charge
Particle
Mass, g
proton
1.6726 x 10
-24
1.00728
1.67 x 10-19
+1
electron
9.1096 x 10
-28
0.000549
-1.67 x 10-19
-1
neutron
1.6749x 10
1.00867
0
0
-24
Subatomic Particles
Particle
Symbol
Charge
Relative
Mass
Electron
e-
1-
0
Proton
p+
+
1
Neutron
n
0
1
Location of Subatomic Particles
10-13 cm
electrons
protons
nucleus
10-8 cm
neutrons
Representation of Atoms
Mass
Number
Atomic
Numbe
r
A
Z
X
Element
Symbol
Atomic Number
Counts the number
of
protons
in an atom
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
Periodic Table
1
11
Na
2
3
4
5
6
7
8
Atomic Number on the
Periodic Table
Atomic Number
Symbol
11
Na
All atoms of an element have
the same number of protons
11 protons
Sodium
11
Na
Counting Protons
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
3) 56 protons
Solution
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
Number of Electrons
 An atom is neutral
 The net charge is zero
 Number of protons = Number of electrons
 Atomic number = Number of electrons
Mass Number
Counts the number
of
protons and neutrons
in an atom
Atomic Symbols
 Show the mass number and atomic number
 Give the symbol of the element
mass number
23 Na
atomic number
11
sodium-23
More Atomic Symbols
16
O
31
P
65
8
15
30
15 p+
16 n
15 e-
30 p+
35 n
30 e-
8 p+
8n
8 e-
Zn
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
Counting Protons, Neutrons &
Electrons
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 _______
_______
_______
Solution
12C
6
13C
14C
6
6
#P __6___
_ 6___
___6___
#N __6___
_ _7___
___8___
#E __6___
_ 6___
___6___
Protons, Neutrons & Electrons
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
3) 67
Solution
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
Atomic Symbols
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-
___________
Solution
16O
A. 8 p+, 8 n, 8 eB. 17p+, 20n, 17e-
8
37Cl
17
C. 47p+, 60 n, 47 e-
107Ag
47
Identifying Elements
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
3)
36X
14
Solution
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
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.
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
Atomic Mass
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
__________
Solution
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__
Calculating Atomic Mass
 Percent(%) abundance of isotopes
 Mass of each isotope of that element
 Weighted average =
mass isotope1(%) + mass isotope2(%) + …
100
100
Atomic Mass of Magnesium
Isotopes
24Mg
=
Mass of Isotope
24.0 amu
Abundance
78.70%
25Mg
=
25.0 amu
10.13%
26Mg
=
26.0 amu
11.17%
Atomic mass (average mass) Mg = 24.3 amu
Mg
24.3
Calculating
Atomic Mass
Gallium is a metallic element found in
small lasers used in compact disc players.
In a sample of gallium, there is 60.2% of
gallium-69 (68.9 amu) atoms and 39.8% of
gallium-71 (70.9 amu) atoms. What is the
atomic mass of gallium?
Solution
Ga-69
68.9 amu x
60.2
=
41.5 amu for
69Ga
28.2 amu for
71Ga
100
Ga-71 (%/100)
70.9 amu x 39.8
=
100
Atomic mass Ga =
69.7 amu
Finding An Isotopic Mass
A sample of boron consists of 10B (mass
10.0 amu) and 11B (mass 11.0 amu). If
the average atomic mass of B is 10.8
amu, what is the % abundance of each
boron isotope?
Assign X and Y values:
X = % 10B
Y = % 11B
Determine Y in terms of X
X
+
Y
= 100
Y = 100 - X
Solve for X:
X (10.0) + (100 - X )(11.0)
100
100
= 10.8
Multiply through by 100
10.0 X + 1100 - 11.0X = 1080
Collect X terms
10.0 X - 11.0 X
=
1080 - 1100
- 1.0 X = -20
X
=
-20
- 1.0
=
Y = 100 - X
% 11B = 100 - 20% =
20 %
10B
80% 11B
Isotopes of Copper
Copper has two isotopes 63Cu (62.9
amu) and 65Cu (64.9 amu). What is the
% abundance of each isotope? (Hint:
Check periodic table for atomic mass)
1) 30%
2) 70%
3) 100%
Solution
2) 70%
Solution
62.9X + 6490 = 64.9X = 6350
-2.0 X = -140
X = 70%
Isotopes of chlorine
Naturally occurring chlorine consists of 75.53%
of the isotope with mass number 35 and
24.47% of the isotope with mass number 37.
What is the average atomic mass of
naturally occurring chlorine?
35
17
Cl
37
17
Cl 17 protons 20 neutrons 17 electrons
17 protons 18 neutrons 17 electrons
Solution
(0.7553)(34.97 u) = 26.41 u
(0.2447)(36.95 u) = 9.04 u
Atomic mass of Cl = 35.45 u
Where Are the Electrons
Located?
This question becomes important since
the nuclear model of the atom proposed
by Rutherford accounted only for the
location of the positively charged
particles. The location of the electrons is
the key to understanding chemistry.