CHEMISTRY BASICS 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

So overall, the nucleus…. Has a positive electrical charge The electrons have a negative electrical charge So this holds the electrons in their orbitals

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 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

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

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….. …..An apartment building 8 apartments / floor “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 example An atom with 3 valence electrons Comes near an atom with 5 valence electrons Will these atoms bond?

Here’s an example Yes! This atom moves its 3 electrons Into the 3 empty places in this atom And the atoms will get together and bond

Another example: An atom with 2 valence electrons Sees an atom with 5 valence electrons Will these atoms bond?

How could they bond? But this atom still needs one for the Octet Rule Move the electrons and this atom is happy… Where could they get it? A 3rd Atom with one electron

Bonds with more than 2 atoms You 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 4 The 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