Understanding Atomic Structure: Protons, Neutrons, and Electrons, Study notes of Chemistry

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Atom

P’s, N’s and e’s oh please!!

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.

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

• 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

Neutral Ca

20 protons from its atomic number (Z)

Therefore it has 20 electrons

Ions

An ion is a neutral atom which has gained or lost an electron.

An ion with a negative charge is called an anion. (it has extra electrons)

An ion with a positive charge is called a cation.

What if N (Nitrogen) gained three electrons?

Its resulting charge is: -

Nitrogen has 7 electrons when it is neutral.

It will need three more electrons to have a - charge.

7+3 = 10

Element Protons Neutrons Electrons Charge

Ar 15 Mo As 11 0 O - 2