Chapter 6 Covalent Compounds. 6.1 Covalent Bonds Sharing Electrons Covalent bonds form when atoms...

Chapter 6

Covalent Compounds

Covalent Compounds

6.1 Covalent Bonds Sharing Electrons

Covalent bonds form when atoms share one or more pairs of electronsnucleus of each atom is attracted to electron cloud of other atom

neither atom removes an electron from the other

Covalent Bonding

6.1 Covalent Bonds Sharing Electrons

Covalent bondsspace where electrons move is called molecular orbitalmade when atomic orbitals overlap

Molecules

6.1 Covalent Bonds Energy and Stability

Noble gases are stable (full octet) (low P.E.)

Other elements are not stable (high P.E.)covalent bonding decreases potential energy because each atom achieves electron configuration like noble gas

6.1 Covalent Bonds Energy and Stability

because P.E. decreases when atoms bond, energy is released i.e., atoms lose P.E. when they bond

loss of P.E. implies higher stability

6.1 Covalent Bonds Energy and Stability

potential energy determines bond lengthat minimum P.E., distance between two bonded atoms is called bond lengthbonded atoms vibratetherefore, bond length is an average length

6.1 Covalent Bonds Energy and Stability

bonds vary in strengthbond energy is the amount of energy required to break the bonds in 1 mol of a chemical compound

bond energy predicts reactivity

bond energy is equal to loss of P.E. during formation

Bond Energies and Lengths

6.1 Covalent Bonds Electronegativity

Atoms share electrons equally or unequallynonpolar covalent bond: bonding electrons shared equally

polar covalent bond: shared electrons more likely to be found around more electronegative atom

6.1 Covalent Bonds Electronegativity

Atoms share electrons equally or unequallydifference in electronegativity can be used to predict type of bond (but boundaries are arbitrary)

I think this concept is important for AP Biology.

Bond Types

6.1 Covalent Bonds Electronegativity

Polar molecules have positive and negative endssuch molecules called dipoles

(“delta”) means partial in math and science

positive end—+

negative end—-

example: H+F-

Electronegativity Difference for Hydrogen Halides

6.1 Covalent Bonds Electronegativity

Polarity is related to bond strengthgreater electronegativity

means greater polarity

means greater bond strength

6.1 Covalent Bonds Electronegativity

Bond type determines properties of substancesmetallic bonds: electrons can move from one atom to another—good conductors

ionic bonds: hard and difficult to break apart

covalent bonds: low melting/boiling points

Properties of Substances with Different Types of Bonds

6.2 Drawing and Naming Lewis Electron-Dot Structures

Lewis structures represent valence electrons with dotsposition of electrons is symbolic (not literal)

shows only the valence electrons of an atom

dots around atomic symbol represent electrons

Lewis Structures of Second-Period Elements

Lewis Structures of Second-Period Elements

6.2 Drawing and Naming Lewis Electron-Dot

StructuresCl2

HCl

6.2 Drawing and Naming Lewis Electron-Dot

StructuresDrawing

1. Gather informationdraw Lewis structure for each atom in compound; place one electron on each side before pairing

determine total number of valence electrons

6.2 Drawing and Naming Lewis Electron-Dot

StructuresDrawing

2. Arrange atomsarrange structure to show bonding

halogens and hydrogen usually make one bond at end of molecule

carbon usually in center

6.2 Drawing and Naming Lewis Electron-Dot Structures

Drawing3. Distribute the dots so that each atom satisfies octet rule (except H, Be, B)

4. Draw the bonds as long dashes

5. Verify the structure by counting number of valence electrons

6.2 Drawing and Naming Lewis Electron-Dot

StructuresPolyatomic Ions

use brackets [] to show overall charge

example:

6.2 Drawing and Naming Lewis Electron-Dot

StructuresMultiple Bonds

sharing two pairs of electrons is a double bond

sharing three pairs of electrons makes triple bonds

example:

6.2 Drawing and Naming Lewis Electron-Dot

StructuresResonance Structures

sometimes, multiple structures are possible

show all possibilitiesexample:

6.2 Drawing and Naming Naming Covalent Compounds

First name: name of first element in formulausually least electronegativerequires a prefix if more than one of them

Second name: ends in –iderequires a prefix if more than one of them

Naming Covalent Compounds

6.3 Molecular Shapes Determining Molecular

ShapesThree-dimensional shape helps determine physical and chemical properties

valence shell electron pair repulsion (VSEPR) theory predicts molecular shapesbased on idea that electrons repel one another

Molecular Shapes

6.3 Molecular Shapes Determining Molecular

ShapesLet’s try some.

COCO2

BF3

CH4

SnCl2SO2

Simple Shapes

Trigonal Planar

Tetrahedral

Bent

6.3 Molecular Shapes Molecular Shape Affects

PropertiesShape affects polarity

compare CO2 and H2Opolarity affects properties (such as boiling point) due to attractions between molecules

Polar Bonds