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 particlesElectron, 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 40Atomic number is 20

40-20 = 20

Practice Individually Finding Protons and Neutrons

MgMn

• Mg• 24-12 = 12• Protons are 12 (because of the atomic

number)• Neutrons are 12 (because of the subtraction)

MnAtomic number is 25Mass number rounded is 55

25 protons55-25 = 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 Ca20 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?+2What 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 0

O -2