Chapter 19,
S
ection 2 Section 1 Review
1
Question 1
Which is the smallest piece of matter that
still retains the property of the element?
A. atom
B. quark
C. neutron
D. proton
Section 1 Review
1
Answer
The answer is A. An atom is the smallest
piece of matter that still retains the property
of the element.
Section 1 Review
1
Question 2
What particles are found in the nucleus of an
atom?
A. protons and electrons
B. protons and neutrons
C. neutrons and electrons
D. quarks and electrons
Section 1 Review
1
Answer
The answer is B.
Electrons are
located in an
electron cloud
surrounding the
nucleus of the
atom.
Section 1 Review
1
Question 3
What is the name of the small particles that
make up protons and neutrons?
Answer
Protons and neutrons are made of smaller
particles called quarks.
Structure of the Atom
1
The Atom
Atomic Number
Represents the number
of
protons
in an atom
Atomic Number on the Periodic
Table
Atomic Number
Symbol
Na
Atomic Number on the Periodic
Table
Atomic Number
Symbol
11
Na
Solution
State the number of protons for atoms of each of the
following:
A. Nitrogen
7 protons
B. Sulfur
16 protons
C. Barium
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
The mass number is not found on the periodic table.
Atomic Mass on the Periodic Table
Atomic Number
Symbol
Atomic Mass
11
Na
22.99
Atomic Mass
Atomic mass is the weighted average mass
of all the atomic masses of the isotopes of
that atom.
Chapter 4
Atomic Structure
Isotopes
•  Isotopes are atoms with the same number of protons but
different numbers of neutrons.
Chapter 4
Atomic Structure
Isotopes
•  To distinguish one isotope of an element from another,
sometimes we say the mass number with the name of
the atom.
For example, this isotope can be called
Sodium -23
And this one is called
Sodium -24
Atomic Mass
Atomic mass is the weighted average mass
of all the atomic masses of the isotopes of
that atom.
Atomic Mass
Atomic mass is the weighted average mass
of all the atomic masses of the isotopes of
that atom.
This is different from the mass number!!
Learning Check
Naturally occurring carbon consists of three isotopes,
Carbon-12, Carbon-13, and Carbon-14. State the
number of protons, neutrons, and electrons in each of
these carbon atoms.
Carbon-12
Carbon-13
Carbon-14
#p
6
6
6
#n
6
7
8
#e
6
6
6