Inside the atom….

There is the nucleus

The nucleus has protons and neutrons

The protons have a positive electrical charge

And the neutrons don’t have any electrical charge

electron

neutron

proton

CHEMISTRY BASICS

So overall, the nucleus….

Has a positive electrical charge

The electrons have a negative electrical charge

So this holds the electrons in their orbitals

electron

neutron

proton

There are several layers of orbitals…

And there are electrons in each layer

So overall,

The positive charge in the nucleus balances the negative charge of the electrons

electron

neutron

proton

So the atom has a neutral charge

But when 2 atoms get close… Something else happens….. The negative electrons of one atom…

Feel the positive nucleus of the other atom

And the electrostatic forces hold them together

It isn’t always a happy meeting…. The electrons on one atom like the nucleus of another atom

But the electrons on that atom don’t like the electrons

And they don’t want the other electrons near

So when they do get close….. The electrons have to move around each other

How they move around each other controls what kind of chemical bond is made

electron

neutron

proton

Not all of the electrons care… Remember the different orbital layers….

The electrons on the outside may see the other atom…

But the electrons close in are happy with their own nucleus

electron

neutron

proton

Not all of the electrons care… So only the outer or valence electrons…

Interact with the other atoms to make a chemical bond

Valence Electrons• When an atom undergoes a chemical reaction,

only the outermost electrons are involved.

• These electrons are of the highest energy and are furthest away from the nucleus. These are the valence electrons.

• The valence electrons are the outermost s and p electrons.

Predicting Valence Electrons• The Roman numeral in the American convention

indicates the number of valence electrons.

– Group IA elements have 1 valence electron

– Group VA elements have 5 valence electrons

• When using the IUPAC designations for group numbers, the last digit indicates the number of valence electrons.

– Group 14 elements have 4 valence electrons

– Group 2 elements have 2 valence electrons

Not all atoms can bond It depends on the number of valence electrons

Think of…..

8 apartments / floor

…..An apartment building

“Eight is Great”

When atoms bond…

If they can’t fill or empty a floor

The atoms don’t want to bond

Here’s how it works….An atom with 2 valence electrons

Wants to Bond with an atom with 6 valence electrons

Atoms aren’t happy – floors aren’t fully empty or full

This atom takes its electrons

And moves them to the other atom

Now both atoms are happy and can bond

Here’s how it works….This is called the “rule of eight”

Or the “Octet Rule”

Remember – “Eight is Great”

If the atom can’t fill or empty the floor…

The Octet Rule isn’t followed…

And the atoms don’t want to bond

Here’s an exampleAn atom with 3 valence electrons

Comes near an atom with 5 valence electrons

Will these atoms bond?

Here’s an exampleThis atom moves its 3 electrons

Into the 3 empty places in this atom

And the atoms will get together and bond

Yes!

Another example:An atom with 2 valence electrons

Sees an atom with 5 valence electrons

Will these atoms bond?

How could they bond?Move the electrons and this atom is happy…

Where could they get it?

But this atom still needs one for the Octet Rule

A 3rd Atom with one electron

Bonds with more than 2 atomsYou bring in a 3rd atom with 1 valence electron

And both atoms move their electrons

Now all 3 atoms have met the Octet Rule

And all 3 atoms will bond together!

Does this work the other way?Will an atom with 5 valence electrons

Move those 5 to an atom with only 3?

It is easier to move 3 electrons than 5

No – 3 electrons will move to the atom with 5

How about this one…It sees 2 other atoms with 2 valence electrons

Will it bond with these 2 atoms?

Yes!

The 2 electrons from the new atoms will move to the atom with 4The Octet Rule is satisfied for all 3 atoms!

One more situation…You have an atom with 8 valence electrons

It sees atoms with 1 and 2 valence electrons

Will the atoms bond?

No!

The first atom has 8 valence electrons

It already meets the Octet Rule

The other 2 atoms don’t have enough to either fully fill or empty their 8

So they won’t bond

What group of atoms have 8 valence electrons?

The Noble Gases (group 18)

Because these atoms have all 8 valence electrons…

They don’t bond (react) with other atoms

That is why the Noble Gases don’t react

They are monatomic atoms

The hermits of the Periodic Table