Download Atoms - TeacherWeb

Atoms
What are atoms?



An atom is the smallest
piece of an element. It is
one million times smaller
than the width of a piece
of hair.
Each type of atom
represents a different
element on the Periodic
Table.
All matter is made of
atoms.
What are the main sections of an atom?
What are the parts of an atom?
Where can each part be found?




An atom has a nucleus
in the center surrounded
by the electron cloud.
An atom has three parts:
protons, neutrons and
electrons.
Protons and neutrons are
found in the nucleus.
Electrons whiz around
outside of the nucleus in
the electron cloud.
Atoms



Each atom is different
because of the number
of protons it has.
This is called the
atomic number.
Atoms are arranged on
the Periodic Table by
their atomic number,
or, by the number of
protons in the nucleus.
Sodium – soft, silver metal that
can be cut with a butter knife and
explodes when in contact with
water
Chlorine – pale, green, poisonous
gas that was used in chemical
warfare in the past
Does an atom have mass?





Atoms are so small that
their mass is measured
in atomic mass units,
amu.
Each proton is 1 amu.
Each neutron is 1 amu.
An electron is 0 amu.
Where is most of the
mass of an atom?
0 amu
1 amu
1 amu
Atomic Mass

The mass of an atom is in its nucleus.

The mass is equal to the number of
protons and neutrons.
 Protons
+ Neutrons = Atomic Mass
Atomic Mass

The number of neutrons in an atom is not
given on the Periodic Table.

To determine the number of neutrons you
round the atomic mass and subtract the
atomic number.
Atomic Mass
atomic mass – atomic
number = number of neutrons
 rounded

(protons + neutrons) – protons = neutrons
Atomic Mass
 Examples
Sodium,
Na, is atomic #11 and has a
mass of 22.98 amu
23 – 11 = 12 neutrons
Chlorine,
Cl, is atomic #17 and has a
mass of 35.45 amu
35 – 17 = 18 neutrons
Does an atom have charges?





Protons are positive (+)
Neutrons are neutral (0)
Electrons are negative (-)
Is the nucleus charged?
Is the electron cloud
charged?
-
+
0
Does an atom have charges?






Protons are positive (+)
Neutrons are neutral (0)
Electrons are negative (-)
The nucleus is positive.
The electron cloud is
negative.
Because an atom has the
same number of + protons
and - electrons, an atom is
neutral.
-
+
0
Electron Clouds




The electron cloud is the area surrounding the
nucleus. The electrons whiz around here.
Most of the area is empty space!
Electrons are arranged into energy levels called
shells.
When the shell is full, it is said to be complete.
Electron configuration



Electrons fit into the energy
levels or shells around a
nucleus in specific
patterns. This arrangement
is called the electron
configuration and it is
given on the Periodic
Table.
If you add the numbers in
the electron configuration,
the sum is the total number
of electrons, which is equal
to the atomic number!
Electrons farther from the
nucleus have more energy.
Electron Configuration





K shell – closest to nucleus, holds 2 electrons
L shell – holds up to 8 electrons
M shell – holds up to 8 or up to18 electrons
N shell – holds up to 18 or up to 32 electrons
There are also O, P and Q shells for a maximum
of 7 energy levels.
Electron Configuration




Example: Sodium
(Na) has an electron
configuration of 2-8-1.
2 electrons in K shell
8 electrons in L shell
1 electron in M shell
Electron Configuration




Example: Chlorine
(Cl) has an electron
configuration of 2-8-7.
2 electrons in K shell
8 electrons in L shell
7 electrons in M shell
Are the shells “complete”?
Sodium:

2 electrons in K shell


8 electrons in L shell


full
full
1 electron in M shell

not full
Since this last shell
is not full, the atom is
not complete!
Are the shells “complete”?
Chlorine



2 electrons in K shell
 full
8 electrons in L shell
 full
7 electrons in M shell
 not full
Since this last shell
is not full, this atom
Is not complete!
Valence Electrons
Electrons in the shell farthest from the
nucleus are called valence electrons.
 These electrons form chemical bonds
with other atoms and give elements their
chemical properties.
 Atoms combine with other atoms to
complete their outermost or last energy
level, called the valence shell.

More on Atoms
Because atoms have the same number of
positive protons and negative electrons,
atoms are neutral. They have no charge.
 If an atom loses or gains electrons, it is
called an ion.
 An ion is a charged particle.

Ions
If an atom loses an electron (-), would it be a
positive or negative ion?
Ions
If an atom loses an electron (-), would it be a
positive or negative ion?
 Positive because you are taking away a
negative charge so there are more protons
than electrons
 Example: Sodium has 11 protons and 11
electrons. If it loses an electron, it has 11
positive protons but only 10 negative
electrons.
Ions
If an atom gains an electron (-), would it be a
positive or negative ion?
Ions
If an atom gains an electron (-), would it be a
positive or negative ion?
 Negative because you are adding a negative
charge so there are more electrons than
protons
 Example: Chlorine has 17 protons and 17
electrons. With an additional electron, chlorine
has 17 positive protons and 18 negative
electrons.
What happens to opposites?