Quick Review
•
Atoms are made up of three particles:
Question: Which of the three particles identifies what element an atom is?
The __________________! (very important)
All atoms of a __________________ element are not exactly alike.
Some elements have atoms with different __________________ (__________________)
Same Element Different Atom-Isotopes
Isotopes - Different Forms of the Same Element
•
In any element, the __________________ of __________________ is __________________
__________________.
•
Unlike the number of protons, the number of __________________ and __________________
can vary within an element without changing the __________________ of the
__________________.
Ex. Carbon (C) ALWAYS has 6 __________________, but it can have anywhere from 6-8
__________________ and 2-10 __________________
Masses of Atoms

A scale designed for atoms gives their small atomic masses in __________________
__________________ __________________ (____________)

An atom of 12C was assigned an exact mass of __________________ amu

__________________ __________________ of all other atoms was determined by comparing
each to the mass of __________________

An atom __________________ as heavy has a mass of __________________. An atom half as
heavy is __________________.
Atomic Mass

Listed on the __________________ __________________

Gives the mass of “__________________” atom of each element compared to 12C

Average atom based on all the __________________ and their __________________
__________________

Atomic mass is __________________ a whole number

Learning Check
o Using the periodic table, specify the __________________ __________________ of each
element (round to the tenths place):
o A. calcium
__________
o B. aluminum
__________
o C. lead
__________
o D. barium
__________
o E. iron
__________
Calculating Atomic Mass

Percent (%) abundance of isotopes

Mass of each isotope of that element

Weighted average =

mass isotope1(%) + mass isotope2(%) + …
100
100
Example: Atomic Mass of Magnesium
o Isotopes
Mass of Isotope Abundance
o
24Mg
=
24.0 amu
78.70%
o
25Mg
=
25.0 amu
10.13%
o
26Mg
=
26.0 amu
11.17%
Atomic mass (average mass) Mg = 24.3 amu
Isotopes

An __________________ is a form of an element that has a different number of
__________________ than “__________________”

Carbon has __________________ isotopes
Other Isotopes

Most atoms have __________________ occurring isotopes including:
o
o
o

When an element is “__________________” it means it has an __________________ number of
__________________ (an __________________ ISOTOPE)
Ions

An atom usually has a __________________ charge. That means it has the same number
of __________________ as __________________
o Remember, a __________________ has a positive charge and an electron has a
__________________ charge

__________________ – an atom that has __________________ or __________________ one or more
electrons and has become charged either __________________ or __________________
Positive Ions - Cations

When an atom __________________ electrons, it becomes more __________________
o Why?
o If you are getting rid of negative particles (__________________) but your number
of positive particles (__________________) are staying the same.
o In other words, you are __________________ __________________ __________________
Examples

What would the charge be if:
o The neutral form of Gold (Au) lost 4 of its 79 electrons. It now has 79
protons and 75 electrons
o The neutral form of Mg lost 2 of its 12 electrons. It now has 12 protons and
10 electrons.
Negative Ions - Anions

When an atom __________________ electrons it becomes more __________________
o Why?
o Electrons have a __________________ charge, so the more you have, the more
__________________ you become
Representing Ions

Ions are represented by placing a “__________________” charge number next to the
atomic symbol

Ex.
o O-2 = oxygen with a negative __________________ charge
o K+ = potassium with a positive __________________ charge
o N-3 = nitrogen with a negative __________________ charge
Periodic Table

The __________________, as they are found on the periodic table, are __________________
atoms and their __________________ is an __________________ of all __________________
o Remember the __________________ __________________ is the average of ALL
__________________, but when we round it for calculating the number of
neutrons, we always get the __________________ __________________ __________________.

Examples
Isotopes

Atoms with the same __________________ of __________________, but different numbers of
__________________.

Atoms of the same element (_____________________ __________________ _______________) with
__________________ __________________ __________________
Isotopes of chlorine
Learning Check
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.
#P _______
_______
_______
#N _______
_______
_______
#E _______
_______
_______
Learning Check
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
Learning Check
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-
___________
Learning Check
An atom has 14 protons and 20 neutrons.
A.
Its atomic number is
1) 14
2) 16
3) 34
2) 16
3) 34
B. Its mass number is
1) 14
C. The element is
1) Si
D.
2) Ca
3) Se
Another isotope of this element is
1) 34X
2) 34X
16
3) 36X
14
14