Atomic Number
the number of protons in an atom
The number of protons establishes the identity
of the element.
On a Periodic Table of Elements, the Atomic Number usually
appears above the chemical symbol.
| Examples: |
|
Remember
Atoms are electrically neutral.
Therefore,
the number of electrons equal the number of protons.
What subatomic particle establishes
the identity of the element?
Practice Problems
Answer the following questions: |
|
| 1. What does an atom’s atomic
number mean?
2. Do atoms have an electrical charge?
Why or why not?
3. Using the Periodic Table state the atomic number,
number of protons, and number
of electrons for an atom
of each of the following elements:
a) nitrogen
b) magnesium
c) bromine
4. For an atom with 26 electrons:
a) How
many protons are in the nucleus?
b) What
is its atomic number?
c) What
is its name and what is its symbol?
|
|
Mass Number
the total number of neutrons and protons in the nucleus
of an atom
Mass number = number of protons + number of neutrons
Examples:
|
Element
|
Symbol
|
Atomic
Number
|
Mass Number
|
Number of Protons
|
Number of Neutrons
|
Number of Electrons
|
| Hydrogen |
H
|
1
|
1
|
1
|
0
|
1
|
| Nitrogen |
N
|
7
|
14
|
7
|
7
|
7
|
| Iron |
Fe
|
26
|
57
|
26
|
31
|
26
|
| Gold |
Au
|
79
|
197
|
79
|
118
|
79
|
What is the significance of the
mass number?
Practice Problems
Answer the following questions: |
|
| 1. What does the mass number
of an atom indicate?
2. For an atom with atomic number of 26 and a mass
number of 56, determine the
following:
a) the
number of protons
b) the
number of electrons
c) the
number of neutrons
d) the
identity of the element
3. How many neutrons are in the nucleus of a bromine
atom that has a mass number
of 80? |
|
|
