Covalent BondsBoth atoms involved (typically

nonmetal) “want” to gain e- to become stable

Electrons are shared in order to allow this to happen

The number of e- shared depends on the element

When atoms share two, or more, electron(s), they form a molecule

Compounds formed with covalent bonds are neutral and, generally, follow the OCTET rule!

All atoms are most stable when they have the electron configuration of a noble gases (THIS MEANS HAVING EIGHT* VALENCE ELECTRONS)* For nonmetals the most common

exception to the octet rule (when forming bonds) is HYDROGEN.

Highly Stable = Noble gas configuration

Hydrogen - will share 1 e-

Oxygen - will share 2 e-

Nitrogen - will share 3 e-

Chlorine - will share 1 e-

Carbon - will share 4 e-

Covalent Bonding in Hydrogen

Electron sharing can occur only when electron orbitals from two different atoms overlap.

Formation of a Covalent Bond

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The number of covalent bonds formed by a nonmetallic element is often directly related with the number of electrons it must share (commonly equivalent to the number of lone pairs of e- the atom has) in order to obtain an octet of electrons.

Types of Covalent BondsSingle - ONE pair of e- sharedDouble - TWO pair of e- sharedTriple - THREE pair of e- sharedCoordinate - Both electrons

being shared originate from a single atom

(a) A “regular” covalent single bond is the result of overlap of two half-filled orbitals. (b) A coordinate covalent single bond is the result of overlap of a filled and a vacant orbital.

- atoms participating in cc bonding generally do not form their normal # of covalent bonds

Ex.: HO2Cl, CO

Types of Covalent Bonds

Electron Dot Structuresof HCl

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Lewis StructuresStructures which represent in a

drawing the arrangement of the atoms and the types of covalent bonds

There are FIVE basic steps to follow.

We’ll use water as an example:).

Step 1:Arrange the atoms!

Remember, Hydrogens always on the periphery

Use the expected bonding patterns to arrange the atoms

• the atom that forms the most bonds is typically in

the middle of the structure.

Step 2:

Count the electronsObtain a total to work from

Step 3:Add the bonds & lone

pairsRemember to give each atom (except H) an “octet” of e- (but, don’t exceed the number of e- available)

Step 4:

Use multiple bonds to fill octets when neededConvert one lone pair to a bonding pair for each pair of e- needed to complete an octet

Step 5:Exceptions to the octet

ruleLess than an octet

Hydrogen & BoronMore than an octet

Phosphorus & Sulfur, Noble gases

Lewis Structures - examples

CCl4PBr3

F2

H2S

NH4+

SO4-2

O3

Double BondsO2

C2H4

CO2

CH2CHCHCH2

NO3-

CO3-2

Triple bondsN2

C2H2

HCN

Exceptions (more than an octet) - Only elements in rows 3 and beyond Why?PCl3 and NCl3

PCl5 but not NCl5

XeF4

SF6

Resonance

Some molecules have measured values of bond lengths which do not support the Lewis structure drawn for the molecule

Example: Ozone, O3

To adequately represent such molecules with Lewis structures, you should draw all possible arrangements of ELECTRONS.

Naming Binary Molecular Compounds

Used only with the second element

Ex. Dihydrogen monoxide

Ex. Tetraphosphorus decoxide

Common vs. Chemical Names

Chemical Name

3-D arrangements of electron pairs

Arrangement of valence electron pairs about a central atom that minimize repulsions between the pairs.Since double & triple bonds are multiple electron pairs in the same location, they act like a single pair when determining the geometry of the molecule

3-D Models of Molecules

(a) Acetylene molecule. (b) Hydrogen peroxide molecule. (c) Hydrogen azide molecule.

Bonding

Molecular Geometry - VSEPR

Bond Polarity & Electronegativity

The difference in the electronegativities (ability of an atom to attract electrons) of the two bonded atoms can be used to define the “polarity” of the bond.

Abbreviated periodic table showing Pauling electronegativity values for selected representative elements.

Bond Polarity

(a) In the nonpolar covalent bond present, there is a symmetrical distribution of electron density. (b) In the polar covalent bond present, electron density is displaced because of its electronegativity.

•Bond LengthsBond lengths are measured

using nucleus-nucleus distances.

For bonds between the same two atoms:Single > Double > Triple

Example: C-O

Molecular Polarity

(a) Methane is a nonpolar tetrahedral molecule.

(b) Methyl chloride is a polar tetrahedral molecule.

Hint: Is the molecule SYMMETRICAL?

Determining Molecular Geometry & Polarity- a Shortcut!Geometry Polarity

A. Look @ center atom1. All bonds non-polar = NON-

POLAR molecule2. Bonds are Polar

a) Only VSEPR bonding groups - go to B.

b) Has VSEPR nonbonding groups = POLAR molecule

B. Look @ attached atoms1. All attached atoms the

same = NON-POLAR molecule

2. One or more different element’s atoms attached = POLAR molecule

Examples- use Lewis structures to guide you

Determine the geometry & polarity (look for symmetry) of these “molecules”:

1. HF2. H2O

3. SF2

4. NI35. SiBr4

6. SeO3

7. CO2

8. CO3-2

9. Na2SO4