Download Atom - Montgomery County Schools

Atom
P’s, N’s and e’s oh please!!
Two regions
Nucleus and the electron cloud.
The nucleus in located in the center of the atom
with an overall positive charge.
The electron cloud surrounds the nucleus and it
has an overall negative charge.
The three particles
Electron, Proton, and Neutron
The electron is found in the electron cloud, it is
very small in mass (to the point that it is
normally a negligible amount).
The charge direction is negative.
The charge value is 1.6022*10-19C
The proton is found in the nucleus.
It has a positive charge direction.
Its charge value is 1.6022*10-19
Its mass is approximately 1 amu.
An amu is atomic mass unit.
The neutron is found in the nucleus.
It has no charge.
Its mass is approximately 1 amu.
Atomic Number (Z)
It is the smaller, whole number in a square on
the periodic table for one element.
It states the number of protons.
Mass number (A)
The mass number is the larger number with a
decimal.
The number states the total number of protons
and neutrons the average atom of that element
has.
The definition of an element is determined by
the number of protons.
To determine the number of neutrons, you need
to do a little subtraction.
First round the mass number to the nearest
whole number (because you either have a
proton or neutron or you do not)
Mass Number (A) – Atomic Number (Z) =
neutrons
Practice!
How many protons and neutrons does Ca
(calcium) have?
Mass number is 40
Atomic number is 20
40-20 = 20
Practice Individually Finding Protons
and Neutrons
Mg
Mn
• Mg
• 24-12 = 12
• Protons are 12 (because of the atomic
number)
• Neutrons are 12 (because of the subtraction)
Mn
Atomic number is 25
Mass number rounded is 55
25 protons
55-25 = 30 neutrons
Electrons
To determine the number of electrons, you need
to know if you have a charged atom (it is an ion)
or a neutron atom.
If it is neutral, then protons = electrons.
Neutral Ca
20 protons from its atomic number (Z)
Therefore it has 20 electrons
Write the symbol
When you write the atomic symbol you do the
following
Ions
An ion is a neutral atom which has gained or lost
an electron.
If an atom has an extra electron (or one more
electron then it has protons), what do you think
happens to the overall charge?
It will become negative by one, because
electrons have a negative charge.
When an atom has a negative charge it is known as
an anion.
What happens if the atom has one less electron
then it has protons?
The atom will have a positive change (it has more
protons which are positive then it has negative
electrons).
This is known as a cation.
So Ca looses two electrons, what will be the
resulting charge?
+2
What if N gained three electrons?
-3
How to determine the number of electrons with
a charge?
Look at the number of protons it has.
Then if it is positive, subtract that positive
charge from the protons and that is how many
electrons are left.
Ca has a +2 charge, it has 20 protons, so it would
have 20-2 = 18 electrons.
Element
Protons Neutrons Electrons
Charge
15
Mo
As
Na
O
0
-2