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Unit 2: The Atom and Periodic Table
ISOTOPES
REVIEW
Atomic
symbol
Atomic
number
Protons
2
Neutrons
Electrons
Atomic
mass
6
11
31
24
37
28
REVIEW… FIX THE ERROR
Protons have a positive
charge and are located on
the outer portion of the
atom.
REVIEW … FIX THE ERROR
The
gold foil experiment
showed that the nucleus
has a dense negative
center, called the
nucleus.
REVIEW … FIX THE ERROR
Neutrons have the same
mass as protons and are
located inside of the
nucleus.
REVIEW … FIX THE ERROR
Electrons have a mass of
1.00 amu and are located
on the outer portion of
the atom.
ISOTOPE DEFINITION
Atoms of same
element with different
numbers of neutrons.
ISOTOPIC NOTATION
A way to represent an
isotope
Mass of Isotope
Atomic Number
Element Symbol
Give Isotopic Notation for Carbon-13
EXAMPLES
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
6
13C
6
14C
6
#P _______
_______
_______
#N _______
_______
_______
#E _______
_______
_______
PRACTICE
An atom of zinc has a mass number of 65.
A.
Number of protons in the zinc atom
1) 30
B.
2) 35
3) 65
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
PRACTICE
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-
___________
ATOMIC MASSES OR MASS NUMBER
A scale designed for atoms gives their small
atomic masses in atomic mass units (amu)
Listed on the periodic table
Average atom based on all the isotopes and
their abundance %
Atomic mass is not a whole number
Na
22.99
ATOMIC MASSES OR MASS NUMBER
Each atomic weight is multiplied by its
percent abundance (expressed as a
decimal).
Add the results together
Round off to an appropriate number of
significant figures.
CALCULATING AVERAGE ATOMIC MASS
Isotopes Mass of Isotope
Abundance
24Mg
=
24.0 amu
78.70%
25Mg
=
25.0 amu
10.13%
26Mg
=
26.0 amu
11.17%
Atomic mass (average mass) Mg =
PRACTICE
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)
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