Chemical Bonding Chapter 12

May the force be with you… Chemical Bond: The force that holds 2 or more atoms together and makes them function as a unit. (Intramolecular force) Bond Energy: The energy required break a given chemical bond

Types of Chemical Bonds Ionic Bonding: Electrons are transferred from one atom to another. (Ions are formed) Metal + Non Metal

Covalent Bonding: Electrons are shared between atoms (NO ions) nonmetal + nonmetal

Some at ms don’t like to share. Electronegativity: Tendency of an atom to attract electrons in a chemical bond.

If one atom in a bond has a greater electronegativity… Polar Covalent Bond: Unequal sharing of electrons. The electrons still are not completely transferred! CovalentPolar CovalentIonic

Determining Bond Polarity Look up the electronegativities of both atoms involved in the bond. If there’s a difference, it’s a polar bond. The bigger the difference, the more polar. Polar bonds? O-H, S-H, P-S, F-S, N-O, H-H

Representing Polar Bonds A dipole is drawn with a plus sign on the lower electronegative element with an arrow going towards the more electronegative element.

More dipoles More on what polarity means to molecules to come in later units.

A closer look at ionic bonding A few observations… Plus, the noble gases don’t react. What does it all mean?

Let’s look at the e - configurations See a pattern?!??!?

The envy of the all the elements… the noble gases When atoms become ions they want to have a noble gas electron configuration – Metals lose electrons to reach noble gas configuration – Nonmetals gain electrons to reach noble gas configuration But what do ionic compounds look like?

LiF

What about nonmetals? A few things to remember… ***ONLY THE VALENCE ELECTRONS ARE INVOVLVED IN CHEMICAL BONDING!! ***ATOMS WANT TO ACHIEVE A NOBLE GAS e - CONFIGURATION A Lewis Structure is a representation of a molecule that shows how the valence electrons are arranged among the atoms in the molecule

Back to noble gases Neon: 1s 2 2s 2 2p 6 = 8 valence electrons Argon: 1s 2 2s 2 2p 6 3s 2 3p 6 = 8 valence e - Xenon: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 = 8 valence e - See a pattern? Octet Rule: Atoms (except for hydrogen & helium) want to be surrounded by 8 electrons in the valence principle energy level. Hydrogen and helium want to be surrounded by 2 valence electrons, known as the duet rule

Steps for writing Lewis Structures 1. Obtain the sum of the valence electrons from all of the atoms. Do not worry about where the electrons come from, just find the sum. 2. Use one pair of electrons (or a line) to form a bond between each pair of bound atoms. 3. Arrange the remaining electrons to satisfy the octet (or duet) rule. 4. Check to make sure you have the right number of electrons and that each atom as the octet rule satisfied.

Your first Lewis Structure: F 2 FF Electrons Bonding Electron Pair Shared Between Both Atoms Lone Pairs of e - -Nonbonding pairs -Not involved with the bonding More lone pairs

Often, a line will represent a bonding pair of electrons FF = F

Lewis Structure for Water

Atoms that really like to share… Single bond – covalent bond in which 1 pair of electrons is shared by 2 atoms Double bond – covalent bond in which 2 pairs of electrons are shared by 2 atoms Triple bond – covalent bond in which 3 pairs of electrons are shared by 2 atoms

Resonance A molecule shows resonance when more than one Lewis structure can be drawn for the molecule

What about polyatomic ions? Same rules apply as with molecules, only add or subtract the charge of the ion from the total valence electrons. Draw the Lewis Structure for CN - Hint: There are 10 total valence electrons.

[ C N ] - **NOTE: The Lewis Structure is put in brackets with the charge outside of it to indicate that the structure is an ion.

There are a few exceptions BF 3 NO NO 2

We’re going 3D! What do these molecules look like? What is their shape? VSEPR Theory VSEPR = Valence Shell Electron Pair Repulsion Electrons have the same charge, so they repel each other. VSEPR works on putting electron pairs (both bonding and lone pairs) as far apart from each other.

Steps for VSEPR Theory 1. Draw the Lewis Structure 2. Count the electron pairs and arrange them so that they are as far apart from each other as possible 3. Determine the positions of the atoms from where the bonding electron pairs are shared. 4. Name the molecular structure based on the positions of the atoms

Oh the possibilities…

Remember… A double or triple bond acts as a single electron pair in VSEPR

Polar Bond = Polar Molecule? What is a polar bond? Nonpolar bonds never produce polar molecules Polar bonds usually produce polar molecules, unless the polar bonds cancel each other out.