Covalent Bonding Addison-Wesley Chemistry Chapter 16 GHS Chemistry 2015 – 2016 S.Fleck

16.1 Objectives O Use electron dot structures to show the formation of single, double, and triple covalent bonds. O Describe and give examples of coordinate covalent bonding, resonance structures, and exceptions to the octet rule.

Covalent Bonds O Nonmetal atoms are sharing electrons to form Covalent Bonds. O A “tug of war” for electrons is taking place between atoms.

Structural Formula O Chemical formulas that show the arrangement of atoms in molecules. O Each dash represents a pair of shared electrons. O Dashes are never used to show ionic bonds.

Single Covalent Bond O A bond in which two atoms share a pair of electrons. FluorineChlorine 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 3s 2 3p 5 *Unshared pairs are also known as lone pairs or nonbonding pairs.

Lets practice our single bonds! O H 2 O O NH 3 – Ammonia O CH 4 – Methane

Now you try HCl

Break into groups of 3 or 4 O Practice drawing orbital notation diagrams, electron dot, and structural molecules for the following molecules … 1. OF 2 2. SCl 2 3. CCl 4 4. NH 3 5. ClF 6. H 2 S

Double & Triple Covalent Bonds O Double bonds – involve 2 shared pairs of electrons. O 2 O Triple bonds – involve 3 shared pairs of electrons. N 2

Coordinate Covalent Bonds O When 1 atom contributes an unshared pair of electrons to a bond. O CO

Covalent Molecule Properties 1. Liquids or gases at room temperature. 2. Low boiling/melting points. 3. Don’t dissolve in H 2 O. 4. Don’t conduct electricity. 5. Mostly made of 2 nonmetals.

Bond Dissociation Energies O Bond Dissociation Energy (BDE) is the energy required to break a bond. O Energy is required to form and to break bonds. O BDE is equal to the energy released when a bond is formed. O The higher the BDE, the stronger the bond.

Bond Dissociation Demo VS.

Demo Reactions 2Mg + O 2  2MgO + Energy C + O 2  CO 2 + Energy

Resonance Structures OZONE *Structures that can be represented by two or more valid electron dot diagrams.

Octet Rule Exceptions O C, O, N, & F always follow the octet rule. ElementHappy with less than an Octet H2 Li2 Be4 B6 Al6

Polarity O The state of having two opposite or contradictory tendencies. O What does this mean in terms of molecules/bonds? O Atoms on either side of a bond can represent the “poles”. O Symmetrical molecules can also have poles.

Polarity vs Bonds O All covalent molecules have covalent bonds. O The bonds can differ in polarity depending on the kind and number of atoms that are joined together. O Nonpolar Covalent O Polar Covalent

Nonpolar Covalent O The bonding electrons are shared equally O The electrons are not favoring 1 pole (atom) over the other. O Example: All of our diatomic molecules O H 2, O 2, N 2, F 2, I 2, Br 2, Cl 2

Polar Covalent O The bonding electrons are shared unequally O The electrons are favoring 1 pole (atom) over the other. O The bonding electrons will have a stronger attraction to the more electronegative atom.

Polar or Nonpolar? O HCl δ + δ - H – Cl OH2OOH2O δ - OH δ + O Greek letter delta – δ, tells us that elements acquire partial charges, because they are sharing, not transferring electrons.

Electronegativity Differences and Bond Types Electronegativity Difference Type of BondExample 0.0 – 0.19Nonpolar CovalentH--H (0.0) 0.2 – 1.9Polar CovalentH--Cl (0.9) ≥ 2.0IonicNa + Cl - (2.1)

Polar Molecules O One end of the molecule is slightly negative and the other slightly positive. O If a polar bond is present, often times the entire molecule is polar. O Dipole – a molecule with 2 poles O H – Cl

Polar Molecules O What about CO 2 ? O = C = O O What is the polarity of the C = O bonds? O What type of molecule is this, polar or nonpolar?

Strength of Bonds O Triple bonds are much stronger than single bonds. O Recall Bond Dissociation Energy – the energy required to break a bond.

HW Packet O Page 3 O Work through questions 1-3. O Finish for homework.

VESPR Theory O Valence Electron Shell Pair Repulsion Theory O This theory is a way of determining the 3D SHAPE of molecules using the number of electron regions around a central atom. O Non-bonded electrons influence the shape (dot diagrams are needed to use this chart). O The VESPR Theory states that the molecular shape will adjust so the valence-electron pairs are as far apart as possible.