Atomic Mass and Isotopes in Atoms
S
ECTION
2: M
ASSES
OF
A
TOMS
Chapter 17: Properties of Atoms
W
ARM
-U
P
:
Which of the following can change
within an element and not change
the identity of that element?
Proton
Neutron
Electron
L
EARNING
G
OALS
Compute the atomic mass and mass
number of an atom.
Identify the components of isotopes.
Interpret the average atomic mass of
an element.
A
TOMIC
M
ASS
The nucleus contains most of the
mass of the atom.
Protons and neutrons are far more
massive than electrons
The mass of a proton and a neutron is
almost 1 atomic mass unit (amu)
A
TOMIC
M
ASS
Different elements are distinguished
by the number of protons that their
atoms have
Every carbon atom has six protons
Every oxygen atom has eight protons
Atomic Number
: the number of
protons in an atom
A
TOMIC
M
ASS
Mass Number
: the sum of the number of
protons and the number of neutrons in a
single atom
If you know the mass number and the
atomic number, you can calculate the
number of neutrons
# of neutrons = mass number - atomic
number
A
TOMIC
M
ASS
Example:
An atom of potassium (K) has a
mass number of 40. How many neutrons
does it have?
I
SOTOPES
Not all atoms of an element have the
same number of neutrons.
Isotopes
: atoms of the same element
that have different numbers of
neutrons
I
SOTOPES
Suppose you have a
sample of boron (B):
Naturally occurring
atoms of boron have
mass numbers of 10
or 11. How many
neutrons are in each
isotope of boron?
I
SOTOPES
Because most elements have more
than one isotope, each element has
an average atomic mass.
Average atomic mass
: the weighted
average of mass of the mixture of its
isotopes
The average atomic mass for each
element is listed in the periodic table!
I
SOTOPES
Four out of every five atoms of boron
are boron-11 and one out of every five
are boron-10.
11
11
11
11
10
4/5(11 amu) + 1/5(10 amu) = 10.8 amu
C
HECK
-I
N
:
What is the mass number of an
isotope of neon (Ne) that has 11
neutrons? What is the average atomic
mass of neon?
Explore the concept of atomic mass in atoms, learn to compute atomic mass and mass number, identify isotopes, and calculate the number of neutrons in an atom. Understand the significance of the atomic number and mass number in determining the characteristics of elements.
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Presentation Transcript
SECTION 2: MASSES OF ATOMS Chapter 17: Properties of Atoms
WARM-UP: Which of the following can change within an element and not change the identity of that element? Proton Neutron Electron
LEARNING GOALS Compute the atomic mass and mass number of an atom. Identify the components of isotopes. Interpret the average atomic mass of an element.
ATOMIC MASS The nucleus contains most of the mass of the atom. Protons and neutrons are far more massive than electrons The mass of a proton and a neutron is almost 1 atomic mass unit (amu)
ATOMIC MASS Different elements are distinguished by the number of protons that their atoms have Every carbon atom has six protons Every oxygen atom has eight protons Atomic Number: the number of protons in an atom
ATOMIC MASS Mass Number: the sum of the number of protons and the number of neutrons in a single atom If you know the mass number and the atomic number, you can calculate the number of neutrons # of neutrons = mass number - atomic number
ATOMIC MASS Example: An atom of potassium (K) has a mass number of 40. How many neutrons does it have?
ISOTOPES Not all atoms of an element have the same number of neutrons. Isotopes: atoms of the same element that have different numbers of neutrons
ISOTOPES Suppose you have a sample of boron (B): Naturally occurring atoms of boron have mass numbers of 10 or 11. How many neutrons are in each isotope of boron?
ISOTOPES Because most elements have more than one isotope, each element has an average atomic mass. Average atomic mass: the weighted average of mass of the mixture of its isotopes The average atomic mass for each element is listed in the periodic table!
ISOTOPES Four out of every five atoms of boron are boron-11 and one out of every five are boron-10. 11 11 11 11 10 4/5(11 amu) + 1/5(10 amu) = 10.8 amu
CHECK-IN: What is the mass number of an isotope of neon (Ne) that has 11 neutrons? What is the average atomic mass of neon?
