Key Terms for your Glossary

• Octet Rule

• Isoelectronic

• Lattice

Why do atoms form bonds?

The Octet Rule

• Atoms bond in order to achieve an electron configuration (EC) that is the _________________________________

• When two atoms or ions have the same EC, they are said to be __________ of each other.

• Eg. Cl- is __________ with Ar

Calculating EN differencesCalculating EN differences• The first step in defining the polarity of a

bond is to calculate electronegativity difference ( EN)

EN = EN large - EN small• E.g. for NaCl, EN = 2.9 - 1.0 = 1.9• Next, estimate from fig 7.12 the % ionic

character: about 65% (60 - 70%)Q-Give the % ionic character for MgO, CH, HCl

MgO = 3.5 - 1.3 = 2.2 … 80% ionic (75-85)CH = 2.5 - 2.1 = 0.4 … 7% ionic (5 - 10)HCl = 2.9 - 2.1 = 0.8 … 20 % ionic (15-25)

Note if % ionic is 20%, then % covalent is 80%

Ionic Bonding

• NaCl = , therefore ________• Na transfers its valence e to Cl = Na+Cl-

• How does this reflect the ____________• _____________________________________

____________________• Cl gains an e, and becomes anion Cl-,

becomes isoelectronic with Ar• http://www.youtube.com/watch?v=9pHOiJRBXRc

Lewis Structure for Ionic Bonds

Tips for Lewis structures dealing with bonds: use two different symbols. For example: o and x’s, or open o’s and filled in o’s

Transferring Multiple Electrons

• What about Mg and O?• Electronegativity = 3.4-1.3 = 2.1= ______• Mg = 2 valence e, O = 6 valence e• What do they need to do to become

isoelectronic with a noble gas?• __________________________________

__________• Try drawing a Lewis Structure for

Magnesium Oxide.

Practice!

• For each bond, determine EN, type of bond, and the Lewis Structure:

• Ca – O

• K – Cl

• Li – Br

• Ba - O

Ionic Bonding with MORE than 2 ions

• Consider Ca and F

• EN = 4.0-1.0 = 3.0 = ________

• ____________________________________________________________________

• So, Ca will form Ca2+ and F will form F-

• How do you think this will happen?

Calcium Fluoride, CaF2

• Ca bonds with 2 F atoms

• Ca2+ + 2F = ____________

Practice!

• For each bond, determine DEN, type of bond, and the Lewis Structure:

• Mg – Cl

• Na – O

• Ca - Br

Conductivity of Ionic Compounds

What happened in our lab?

Conductivity of Ionic Compounds

• Why are ionic compounds good conductors when dissolved and not in their solid state?

• What is required for electrical conductivity?

• What is the structure of ionic compounds in the liquid, solid, and dissolved states?

Conductivity of Ionic Compounds

• An electrical current can flow _______________________________________________________________

• Is there a mobile charge in solid NaCl?• Salt crystals are held together by rigid strong

ionic bonds, in a ____________.• __________-, not Ladas :O)• In a solid state, ions can’t move very much.

There is no mobile charge, that’s why solid NaCl _______________________

What do you think?

• What happens when we dissolve NaCl in H20?

Aqueous NaCl as a conductor

• When dissolved, the lattice __________

• Ions are free to move around = ________________________

• Salt water is a __________________

• See Figure 3.14 pp.79

Stalagmites and Stalactites

• Crystal columns that form when water containing dissolved lime (CaO) drips down.

• From limestone (CaCO3)• Clear ionic solution over a

crystal of the same compound = will continue the arrangement of the crystal

Covalent Bonds – Key Terms

• Diatomic elements

• Double bond

• Pure covalent bond

• Triple Bond

Covalent Bonds

• What happens when the EN is very small?• _________________ (shared e)• What happens when the EN is 0?• ____________________________________

_______________________________________________________________

• This happens in ___________________• http://www.youtube.com/watch?v=UR4eG60jjQQ

•

Diatomic elements

• I Bring Clay For Our New House

• Have No Fear of Ice Cold Beer

• ___________________________________

• Only 7 elements that exist as pure covalent diatomic elements

• There are numerous other molecules that diatomic, but not with the same element

• Noble gases do not form diatomic elements

Carbon – The Master Bonderbetween C and H =

_________________________________really small difference, almost __________

Eg. Methane CH4

Each H shares 1 e with C, C shares each of it’s 4 e with H = ____________________________________________

When checking your Lewis Diagrams, count the shared e as If they belong to each of the bonding atoms.

Practice!

• Show how each pair of elements forms a covalent compound, and give the compound formula.

• H and O

• Cl and O

• N and H

• I and H

Multiple Covalent Bonds

• Some atoms need to share more than one pair of electrons.

• They may need to share 1, 2, or 3 pairs.• Eg. Diatomic molecule of _______________

Double and Triple Covalent Bonds

• These bonds can form between ______________________.

• Eg. Carbon Dioxide (CO2)

• * Tip* - make sure that each element has 8 e by drawing circles around them in different colours.

Double and Triple Covalent Bonds

• Atoms that share three pairs of e form _________________________

• Eg. Diatomic N

Practice!

• CS2

• C-H-N

• CH2

Polar Covalent Bonds“Monkey in the Middle”

Polar Covalent Bond

EN the is _______________

• Although higher _____________________________, the is not high enough to make an ionic bond.

is high enough to make the bonding pair want to be _____________________________________________

-/+ Partial Charges (

• Eg. O – H• EN of O = __________• _____________________ = _______• Therefore between 0.5 and 1.7• O has a higher EN so it attracts

e more strongly and therefore has a slightly more ______________________

• Also known as _________________________

• H has a __________________

What About Water H20?

• What do you think the partial charges would be?

Water vs. Carbon Dioxide

Predicting Molecular Shape

• Why is H2O bent and CO2 straight?

• Look at the Lewis Structures• e- pairs that are not involved in bonding are

called _____________• e- pairs are that involved in bonding are called

______________• e- pairs are arranged around molecules so that

they have a ____________________________________

Shape of a H20 Molecule

Water

• Water is a polar molecule, as it has two negatively charged parts (the electron pairs that are unbound) and two positive parts (the Hydrogen atoms). These opposite charges are attracted to each other. This holds water molecules together which explains why water is a liquid at room temperature while almost all other similar sized molecules are gases. This also accounts for water's excellent dissolving capacity for other charged substances such as salt, and why uncharged substances (non polar) such as oil do not mix readily with water.

Shape of a CO2 Molecule

• Each double bond uses 2 bond pairs - which are then thought of as a single unit. Those two double bond units will try to get as far apart as possible, and so the molecule is linear. The structure we've drawn above does in fact represent the shape of the molecule.

Other Examples

• What about ammonia (NH3)? Or methane (CH4)?

LOTS of new stuff tonight!!

• 2nd half of lesson #3 on Monday (polarity of bonds)

• We will be taking up the test Monday• We will be doing an activity with molecular

building kits as well.• Please if you haven’t done the

readings…..DO THEM!• Make sure that all homework for Lessons

1,2,3 is complete so that you can benefit and understand the activity.