HOW THE WORLD WORKS, ACCORDING TO CHEMISTRY Part 8a

Part 8a Molecular Shape

THE MODEL WE WILL USE TO DETERMINE MOLECULAR SHAPE IS CALLED _________ (V_________ S_________ E__________ P________ R_______________)

THE ELECTRON PAIRS AROUND THE ____________ ATOM OF A MOLECULAR COMPOUND REPEL EACH OTHER, AND TRY TO GET THIS DETERMINES THE SHAPE OF THE MOLECULE

I HATE YOU!! GET AWAY FROM ME!!! CENTRAL ATOM PERIPHERAL ATOM ELECTRONS ON CENTRAL ATOM

VSEPR STEPS 1 and 2 1. Draw the _____________________ 2. Count the ____________________ _______________________________ What molecular shape gets the electrons as far from each other as possible?

Step 1 and Step 2: BeH 2 Note: compounds of beryllium (Be) are often exceptions to the Octet Rule. Beryllium may have only ____________ electrons pairs around it.

The pairs of electrons around the central atom are referred to as Think of these as balloons. What shape allows the “balloons” to get as far from each other as possible?

For 2 electron clouds around the central atom… The molecular geometry is The bond angle is

Compounds of BORON (B) are also often exceptions to the Octet Rule. H B H H Step 1 and Step 2: BH 3 They often have ______ electron clouds around the central boron.

For 3 electron clouds around the central atom, (no unshared pairs on the central atom)… The molecular geometry is The bond angle is

METHANE GAS (CH 4 ) is natural gas

Step 1 and Step 2

When there are ______ electron clouds around the central atom (none of which are unshared pairs), this shape is called _______________________

Build a “ball and stick” model of methane. WHITE – HYDROGEN BLACK – CARBON SINGLE BOND:

To draw a more 3-D Lewis structure: This shape of bond, indicates that the atom is sticking forward. This shape of bond, indicates that the atom is sticking back.

UNSHARED PAIRS ON THE CENTRAL ATOM Unshared pairs occupy a position in space, so any unshared pairs _______________________________ are included in the pairs of electrons that affect the shape.

AMMONIA (NH 3 )

Step 1 and Step 2

NH 3 : around the central atom, there are ____ electron clouds However, ____ of those clouds is an unshared pair, so the molecular geometry is called: _______________________________

Build a model of NH 3 BLUE - NITROGEN

Draw the Lewis structure with the 3-D bonds.

WATER

Step 1 and Step 2

For H 2 O: Around the central atom, there are ______ electron clouds However, ______ of those clouds are unshared pairs, so the molecular geometry is called_______________

Build a water molecule… RED - OXYGEN

Draw the Lewis structure of water with 3-D Bonds. Whenever you have only 3 atoms, they must ______________________ _______________________________ so the bonds you draw ___________ _______________________________

When drawing a linear molecule, you ALWAYS SOMETIMES NEVER use 3-D bonds.

Unshared pairs on the central atom take up more room than shared pairs because….

Which one of the molecules below has an unshared pair on the central atom? How do you know?

Double Or Triple Bonds On The Central Atom count as a ____________________________ in molecular geometry

SULFUR DIOXIDE SO 2

Step 1 and Step 2

SO 2 : Around the central atom, there are _____ electron clouds However, _____ of those clouds is an unshared pair, so the molecular geometry is called_______________

Build a model for SO 2 normally… sulfur is red – like oxygen. However, because it has more than 2 bonds to it, you must use a black atom. For a double bond -

MORE THAN ONE CENTRAL ATOM Molecules may have more than one central atom. A central atom is an atom that is _____________________________________ within a compound. When there is more than one central atom in a molecules, you must determine the shape around _____________________________________

ETHANOL - C 2 H 5 OH

Build an ethanol molecule.

CARBON #1 M. G. ____________________ CARBON #2 M. G. ____________________ OXYGEN M. G. ____________________

Our next step will be: 8b POLARITY