Atomic Bonds

FIRST: Pass up your homework “exit ticket”

THEN: Classify the following as elements, compounds, atoms, or molecules

1. A gold (Au) nugget

2. The smallest piece of water (H2O) possible.

3. A glass window (SiO2)

4. The smallest piece of sodium (Na) possible

Answers• A gold nugget is an element, since it is made of many

gold atoms (and only gold atoms!)

• The smallest piece of water is a single water molecule. Any smaller than that, and it’s not water!

• SiO2 (glass) is a compound, since it is made up of several types of atoms joined together. [note: the smallest piece of glass possible would be a single molecule of SiO2]

• Since sodium (Na) is an element, the smallest sample possible is a single sodium atom.

Atomic Bonds [aka chemical bonds]

• What is a bond?

• So what is an atomic bond?

• An attractive force between 2 atoms.

Please Copy the following chart into your notes:

Type of bond What happens Example molecule

What causes atomic bonds?

• When atoms change how they are bonded to one another, that is called a chemical reaction.

• Why do chemical reactions happen?

What’s more likely? Things go from high energy to low!

• Water flowing down a cliff to make a waterfall… or water flowing up?

• Falling down a flight of stairs or falling up?

• Dropping an egg and making a mess or dropping a broken egg and getting one that’s back together?

It’s all about Potential Energy• Atoms bond to get a

lower energy configuration.

Arrows indicate increasing potential energy

But Why? ELECTRONS DETERMINE HOW ATOMS BOND

• Atoms that have a full outer energy level are very stable. This is the driving force of bonding reactions.

• Atoms bond together in a way that fills their outermost electron energy level. (2 or 8)

• This is the lowest energy configuration possible.

Ionic Bonds

• An atom loses 1 or more valence electrons, giving it a positive charge.

• Another atom gains the electron(s) and becomes negatively charged

• + & - ions attract.

Na Cl

e-e-

e-

e-

e-

e-e-

e-

-+

Covalent bonds

• 2 atoms share a pair of valence electrons

He-

He-

It’s all about Energy

Ne

NeNe

2-7 NotStable

2-8 VERYStable

2-8-1NotStable

TWIST: Polar Covalent Bonds• In a polar covalent bond, a pair of electrons is

shared between two atoms… unevenly

• One part of the molecule now has a small – charge, and the other has a small + charge

Electron Sharing

100%Non-polar covalent

Polar covalent

100%Ionic

What types of bonds atoms formAlmost always lose electrons

Don’t bond

Almost always gain electrons

Polar (greedy for electrons)

Mostly non-polar

Metals (electrons “float” around nuclei)+ -

To the Video!

• HOMEWORK: Read 2-1, answer SR #1,2,4

Modeling Atomic Bonds

• Work in a group of NO MORE THAN 3, and explore the foam board bonding models.

• As you do so, complete the worksheet you picked up.