Mini-Lessons
The Atom
Mini-Lesson:
Parts of the Atoms
What is an atom made
of?
Protons
+1 Charge
1 amu (atomic mass unit)
1amu=1.7 * 10-24 g
Neutrons
0 (neutral) charge
1amu
The protons and
neutrons are
located within the
nucleus. It has very
little volume but
almost all of the
mass of the atom
so it is VERY dense!
Electrons
-1 Charge
Found around the nucleus in an electron cloud
Virtually no mass
What’s in The Box?
Element Symbol
Zr is Zirconium
Atomic Number- tells the number
of protons in one atom of the
element
Zr has 40 Protons
(therefore it also has 40
electrons)
Atomic Mass (Mass Number)
Tells number of protons and
neutrons combined (40 + ? =
91)
Elements And Their
Atoms
Each element has a
unique atomic number
The number of protons
for an element’s atom is
constant and unique
The number of electrons
will equal the number of
protons UNLESS the
atom is an ion
An element’s atom can
have a different
number of neutrons
Since the mass of an
atom depends on the
protons and neutrons,
the mass of an element
can change
To find neutrons,
subtract the atomic #
from the atomic mass
Mini-Lesson:
Isotopes and Ions
What is the Charge of
an Atom?
In a typical atom you will have the same
number of protons and electrons, what
charge does this give the atom?
0 Charge, or it is neutral!
Can a proton leave an
atom??
No
If it did you would have a NEW
element…more on this later!
Can an electron leave or
join an atom??
Yes!
This is called an Ion
If the atom is missing an electron it
will be a Positive Ion.
If the atom gains and electron it will
be a Negative Ion.
Can the number of neutrons
change?
Yes!
This is called an isotope, it will
cause the MASS of the atom to
change
For Example…
Look at the periodic table and find Carbon
What is the atomic number?
What is the mass number?
“Carbon 12” is the most common form of Carbon
But you’ve heard of Carbon 14…That is an isotope of
Carbon – it has two more neutrons, adding 2 amu to
its mass…but it still has only 6 protons
To name an Isotope
Element Name – Mass #
Isotope of Different Element
Element D has 6 protons and 7 neutrons
Element F has 7 protons and 7 neutrons
Different Element
Element J has 27 protons and 32 neutrons
Element L has 27 protons and 33 neutrons
Isotope
Element T has an atomic number of 20 and an
atomic mass of 40.
Element Z has an atomic number of 20 and an
atomic mass of 41.
Isotope
Mini-Lesson:
Electron Arrangement
and Bohr Model
Characteristics of Electrons
 Extremely small mass
 Located outside the nucleus
 Moving at extremely high speeds in a
sphere
 Have specific energy levels
LecturePLUS Timberlake
14
Electrons have special
rules….
You can’t just shove all of the electrons into
the first orbit of an electron.
Electrons live in something called shells or
energy levels.
Only so many can be in any certain shell.
The electrons in the outer most shell of
any element are called valance electrons.
Created by G.Baker
www.thesciencequeen.net
Electron Levels (Shells)
 Contain electrons that are similar in energy
and distance from nucleus
 Low energy electrons are closest to the
nucleus
 Identify by numbers 1, 2, 3, 4, 5, 6…..
 The first shell (1) is lowest in energy, 2nd level
next and so on 1<2<3<4
LecturePLUS Timberlake
16
Atom Models
There are two models of the atoms we
will be using in class.
Bohr Model
Lewis Dot Structure
Created by G.Baker
www.thesciencequeen.net
Bohr Model
The Bohr Model shows all
of the particles in the
atom.
In the center is circles.
Each circle represents a
single neutron or proton.
Protons should have a plus
or P written on them.
Neutrons should be blank
or have an N.
In a circle around the
nucleus are the electrons.
Electrons should have a
minus sign or an e.
Created by G.Baker
www.thesciencequeen.net
-
+
+
-
Nucleus
1st shell
2nd shell
3rd shell
Adapted from http://www.sciencespot.net/Media/atomsfam.pdf
Created by G.Baker
www.thesciencequeen.net
Order of Electron Filling
All electrons in the same energy level have similar energy.
Shell 1
2 electrons
Shell 2
8 electrons
Shell 3
18 electrons (8 first, later 10)
Order of filling for the first 20 electrons
Shell
LecturePLUS Timberlake
1
2e
2
8e
20
3
8e
4
2e
So let’s try it….
How to draw a Lithium atom
First, look at the Periodic Table
Second, determine the
number of protons (Look @
the atomic number)
Then determine the number of
neutrons (Atomic mass –
atomic number)
Then determine the number of
electrons (Look @ the atomic
number)
Created by G.Baker
www.thesciencequeen.net
3
Li
Lithium
7
So let’s try it…. Protons = 3
3
-
+
+
Li
+
-
Lithium
-
7
Electrons = 3
2 in the
1st
shell, 1 in the
2nd
shell
Neutrons = 4
(7-3=4)
Created by G.Baker
www.thesciencequeen.net
Lewis Dot Structure
Just shows the valance electrons.
How many does Lithium have?
Write the symbol
Li
Mini-Lesson
Forces in the Atom
The Fantastic Four!
What Forces Keep an Atom Together
?
There are four natural forces that are
responsible for the behavior of an
atom’s particles . . .
The Fantastic Four!
Forces In The Atom
Gravitational Force
Attractive force between all objects in the universe
Gravity depends upon mass of and distance between
objects…
This force is not very strong in the atom
Electromagnetic Force
Opposites attract; likes repel
Protons & electrons
Electrons and Nucleus
More Forces in the
Atom
Strong Force
Holds protons and neutrons together to make the
nucleus
Greater than electromagnetic force between protons
(since the protons would repel each other)
Weak Force – Yes, it’s a very weak force
Deals more with radioactive decay and nuclear fusion
Weak forces are important because they are
responsible for stabilizing particles through the
process of radioactive decay, in which a neutron in the
nucleus changes into a proton and electron.
Mini-Lesson
Groups, Periods, and
The Lewis Dot Structure
Lewis Dot Structure
The Lewis Dot
Structure is a bit
different from the
Bohr model.
It only shows the
element symbol
and it’s outer most
electron shell, the
valence electrons.
Created by G.Baker
www.thesciencequeen.net
-
-
-
+
+ + +
-
-
+ + +
+
-
-
••
•O •
•
•
-
The Periodic Table
Columns are called
groups or families, and
as family members,
they have similar
properties
Rows are called
periods. They do not
share properties, but
properties change as
one goes from left to
right
The Periodic Table
The first element in a period
is always an extremely active solid.
The last element in a period is always
a particularly inactive gas. These are
referred to as the “noble gases.”