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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
