Chemistry Review Part 2- Molecules and Bonding

Bonding Basics Understanding basic bonding is important in biology because the ability of elements and molecules to bind with one another is the basis of functions in our bodies!

Chemistry & Biology Remember, Without Chemistry…there is no Biology!

Covalent Bond Sharing of electrons between two atoms A single bond consists of 2 shared electrons, which occupy the valence shell of both atoms ▫Double bond = 4 electrons ▫Triple bond = 6 electrons

Lewis Structures A line represents 2 electrons, shared in a covalent bond Dots represent electrons that are held by only one atom (lone pairs) Only valence electrons are shown Each atom should have a total of 8 electrons (except H and He which hold 2)

Guidelines for Drawing Lewis Structures Carbons make up core Add Hs last (they can’t connect anything) Remember how many bonds each atom will make (using the periodic table

On your Whiteboard Draw or make: C 3 H 8 CH 3 OH CF 2 O 2 H 2

Double/Triple Bonds When the molecule has fewer electrons than required to have all single bonds, double or triple bonds may form E.g. O2

Draw and or make: N 2 HCOOHHCN

Polar vs. Non-Polar Covalent Bonds NonpolarPolar Electrons shared equally Both atoms have similar electronegativity (affinity for electrons) Neither atom ends up with any charge Electrons are not shared equally 1 atom is more electronegative (O, F, N, Cl are the usual culprits) Electronegative atom ends up with a partial – charge since they have the electron more often Other atom ends up with a partial + charge as they are deprived of the electron

Electronegativity – hunger for electrons

Water as a polar molecule

Non-PolarPolar

Ion Formation Some atoms more easily give up electrons (1 st and 2 nd columns) to end up with a full valence shell These electrons can be stripped by atoms in the 7 th column (need 1 e) Forms ions

Ionic Bonding Opposites attract! Significantly weaker than a covalent bond Can also occur between ionic molecules

It’s a continuum Ignore if you’re overwhelmed

Hydrogen Bonds Weak attraction between the partial charges of polar covalently bonded molecules In water, between O and H Means partial

Bonding Determines Properties of Molecules HydrophobicHydrophilic Mostly non-polar bonds No partial charges No H-bonding or ionic bonding Oils, waxes, fats, rubbers etc. AKA fat soluble Mostly polar and ionic bonds Partial and full charges H-bonding and ionic bonding Exhibit cohesion – stick together Salts, sugars, etc. AKA water soluble

Properties of Polar Molecules Like Water CohesionAdhesion Sticks to itselfSticks to other things

H-bonds and Ions + and – attract whether they are full or partial charges The stronger the charges, the stronger the attraction

Water dissolves hydrophilic nd.cc.mn.us/biolog y/Biology1111/anim ations/dissolve.htm l nd.cc.mn.us/biolog y/Biology1111/anim ations/dissolve.htm l om/physsci/chemis try/essentialchemis try/flash/molvie1.s wfhttp:// om/physsci/chemis try/essentialchemis try/flash/molvie1.s wf

The hydrophobic effect Non-polar do not attract water but water still attracted to itself so water forms a “cage” around the non-polar molecule.