Download Atomic Mass

Chapter 4
“Atomic Theory
and Structure”
 OBJECTIVES:
 Explain
Dalton’s atomic theory.
 Identify the parts of an atom,
their location, charge, and
relative mass.
 Determine the numbers of
subatomic particles in an atom.
Democritus’s Atomic Philosophy

Democritus created the idea
that all matter is made up of
various imperishable,
indivisible units, which he
called atoma.
This idea was soon
rejected and forgotten.

Dalton’s Atomic Theory
1)All elements are
composed of tiny
indivisible particles
called atoms.
John Dalton
(1766 – 1844)
2) Atoms of the same
element are identical.
Atoms of different
elements are different.
3) Atoms of different elements combine
in simple whole-number ratios to
form chemical compounds
4) In chemical reactions, atoms are
combined, separated, or
rearranged, but never changed into
atoms of another element.
What are the main components of
the atom?

Atoms have two main regions
1.
________________
2.
________________
 One
change to Dalton’s atomic
theory is that atoms are divisible
into subatomic particles:
 Electrons
 Protons
 Neutrons
The Subatomic Particles
Location
Proton
Neutrons
Electrons
Charge
Relative
mass in
amu
Function
Atom Math


Protons: atomic number
Electrons: protons – charge
(same as protons if atom is neutral)

Neutrons: mass number – atomic number
protons: ________
electrons: ________
neutrons: ________
Atom Math
Atomic number:
• number of protons
• (also electrons IF atom
is neutral)
Atomic mass:
• Average value of all isotopes
• called mass number when
rounded to nearest whole
number
• Mass Number equals
protons + neutrons
Atomic Number
Atomic number of an element is the number of protons in
the nucleus of each atom of that element.
Element
Carbon
Phosphorus
Gold
Atomic
Number
Number
of
Protons
Number
Number
of
of
Electrons Neutrons
Ions
 When
an atom loses or gains
electrons it is called an ion
 Loses—positive ion
 Gains—negative ion
Ions-counting electrons
# electrons
•
•
•
•
•
-2
O
Al +3
Be +2
-1
Br
+1
K
gain/lost
Isotopes
Atoms of the same element can
have different numbers of
neutrons.
Thus, different mass numbers.
Naming Isotopes
 We
can also put the mass
number after the name of the
element:
 carbon-12
 carbon-14
 uranium-235
 uranium-238
Isotopes are atoms of the same element having
different masses, due to varying numbers of
neutrons.
Isotope
Protons Electrons
Neutrons
Hydrogen–1
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium)
1
1
0
1
1
1
1
1
2
Nucleus
Isotopes
Elements
occur in
nature as
mixtures of
isotopes.
Isotopes-counting neutrons
Mass #
•
•
•
•
•
Oxygen-18
Aluminum-25
10Be
79Br
Potassium-41
# Neutrons
Relative Atomic Mass

Atoms are very small particles. It is very difficult to do
calculations with the mass of an atom measured in grams.


Exmp. The mass of an atom of oxygen is
0.00000000000000000000002657 g.
Instead, scientists use a relative unit of mass based on the
mass of the nuclide Carbon-12 called the atomic mass
unit.

Exmp. The mass of an oxygen atom is
16 amu.
How are atomic number, atomic
mass, and charge calculated?
Atomic number = ______________
Mass Number= Protons + ______________
Charge = Protons - _________________
Calculating Protons, Neutrons,
and Electrons

Protons = _________________

Neutrons = Mass Number - ________

Electrons = Protons - __________
Complete Symbols
Contain the symbol of the element,
the mass number and the atomic
number.
Mass
Superscript →
number

Subscript →
Atomic
number
X
Review Subatomic Particle Counting
1.
How many protons, neutrons, and electrons are in Chromium?



2.
P = atomic number = 24
N = mass # - protons = 52 - 24 = 28
e = protons – charge = 24 – 0 = 24
How many protons, neutrons, and electrons are in
the element with an atomic number of 57?



P = atomic number = 57
N = mass # - protons = 139 - 57 = 82
e = protons – charge = 57 – 0 = 57
Chapter 4
Part 2“Isotopes”
Atomic Mass

The average atomic mass: is based on
the abundance (percentage) of each
variety of that element in nature.
To calculate the average
atomic mass:
 Multiply
the atomic mass of
each isotope by its
abundance percentage
(expressed as a decimal),
then add the results.
Atomic Masses
Atomic mass is the average of all the
naturally occurring isotopes of that element.
Isotope
Mass #
% in nature
Carbon-12
98.89%
Carbon-13
1.11%
Carbon-14
<0.01%
negligible
Carbon = 12.011
Average Atomic Mass
Rubidium has two common isotopes, Rb-85
and Rb-87. If the abundance of Rb-85 is 72.2%
and the abundance of Rb-87 is 27.8%, what is
the average atomic mass of rubidium?
On Your Own
Titanium has five common isotopes: 46Ti
(8.0%), 47Ti (7.8%), 48Ti (73.4%), 49Ti (5.5%),
50 Ti (5.3%). What is the average atomic mass
of titanium?
Poll everywhere response
Argon has three naturally occurring isotopes:
argon-36, argon-38, and argon-40. Based on
argon’s reported atomic mass, which isotope
do you think is the most abundant in nature?
Calculate the weighted average atomic
mass of the following mix of isotopes:
Isotope
Total
Number
Total
Mass
A
15
45
B
5
10
Mass of one
Atom
Percent
Abundance
(in decimal form)
Beanium:
Atomic and Isotopic Mass
Purpose:
• To illustrate the relationship between
isotopic mass, isotopic abundance, and
atomic mass.
Data Table:
Weighte
Total #
d
Total
Mass of Percent
of atoms
abundan Isotopic average
mass of
one
mass
in
atomic
ce
sample
atom
(in decimal form)
sample
mass for
beanium
Black
beanium
White
beanium
Spotted
beanium
Total
beanium
sample
1
Related Questions: Show all work.
1. Chlorine:
a. Chlorine exists in nature as chlorine-35 (% abundance = 75%) and
chlorine-37 ( % abundance = 25%). Calculate the atomic mass of chlorine.
b. What is the essential difference in the structure between the chlorine
atoms found in question
Number 1a?
2. Oxygen: Oxygen gas consists of isotopes with atomic masses of 16.00,
17.00, and 18.00 amu. Their abundances are 99.76%, 0.04%, and 0.20%
respectively. What is the atomic mass of oxygen?
3. Nitrogen: nitrogen has two isotopes, N-14 and N-15, with masses of
amu and amu respectively. If the atomic mass of nitrogen is 14.00674
amu, what is the abundance of each
isotope?
Data Table:
Weighte
Total #
d
Total
Mass of Percent
of atoms
abundan Isotopic average
mass of
one
mass
in
atomic
ce
sample
atom
(in decimal form)
sample
mass for
beanium
Black
beanium
White
beanium
Spotted
beanium
Total
beanium
sample
1
Lab Report – Related Questions
1. Chlorine: Chlorine exists in nature as chlorine-35 (%
abundance = 75%) and chlorine-37 (% abundance =
25%). Calculate the atomic mass of chlorine.
2. Oxygen: Oxygen gas consists of isotopes with atomic
masses of 16.00, 17.00, and 18.00 amu. Their
abundances are 99.76%, 0.04%, and 0.20% respectively.
What is the atomic mass of oxygen?
3. Nitrogen: nitrogen has two isotopes, N-14 and N-15,
with masses of 14.0031 amu and 15.001 amu
respectively. If the atomic mass of nitrogen is 14.00674
amu, what is the abundance of each isotope?
What’s on the quiz?
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Vocabulary
Dalton
Counting
Ions
Isotopes
Weighted average atomic mass
Friday, September 20, 2013
BR: What is the structural
difference between Chlorine-35
and Chlorine-37?
Dalton
Counting
Ions
Isotopes
Average atomic mass
Basic Atomic Theory Review
Basic Atomic Theory Review
Basic Atomic Theory Review
Basic Atomic Theory Review
Friday, September 20, 2013
EQ: What characteristics of the
atom are explained by the modern
atomic theory?
Quiz
•
•
•
•
•
Dalton
Counting
Ions
Isotopes
Average atomic mass