Covalent Bonding (I) Sharing of Electrons in Single Bonds

Covalent Bonds: Sharing of Electrons Non-metal with Non-metal Sharing of electron(s) –Non-polar (equal sharing of electrons) –Polar (uneven sharing of electrons) Weak bonds…low melting points –Single, double and triple bonds

Definitions Molecule: a neutral group of atoms united by covalent bonds. Nonpolar bond: a bond that has an equal sharing of bonding electrons. Polar bond: a bond that has an unequal sharing of bonding electrons. Unshared pair: a pair of electrons that is not involved in bonding but is instead held exclusively by one atom.

Nonmetal with Nonmetal Group 4A, 5A, 6A, 7A and Hydrogen Review of Lewis Dot Diagrams –Group 4A:C –Group 5A:N –Group 6AO –Group 7AF –HydrogenH

Covalent bonding FF l Fluorine has seven valence electrons l A second F atom also has seven l By sharing electrons …

Covalent bonding FF l By sharing electrons l Both end with full orbitals (stable octets) 8 Valence electrons

The Octet Rule Again with one Exception Most elements want to achieve 8 electrons after sharing in the their outer valence shell. Hydrogen wants to achieve 2 electrons after sharing in its outer valence shell. Shared electrons get counted for both partner atoms involved in the sharing of electrons.

Water H O Each hydrogen has 1 valence electron. Each hydrogen wants 1 more electron to get up to 2. Oxygen has 6 valence electrons. Oxygen wants 2 electrons to get up to 8. They share to make each other happy.

l Put the pieces together l The first hydrogen is happy l The oxygen still wants one more H O

Water l The second hydrogen attaches l Every atom has full energy levels l A pair of electrons is a single bond HO H H HO

11 Ammonia l NH 3 l N has 5 valence electrons, but wants 8 in a covalent compound. l H has 1 valence electrons, but wants 2 in a covalent compound. l 4 atoms with 3 bonds N H

N H H H Ammonia l Draw in the bonds l All 8 electrons are accounted for l Everything is full

Carbon dioxide l CO 2 - Carbon is the central atom (I have to tell you this) l Carbon has 4 valence electrons l Wants 4 more l Oxygen has 6 valence electrons l Wants 2 more OC

Carbon dioxide l Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short O C

Carbon dioxide l Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short O C O

l The only solution is to share more l Requires two double bonds l Each atom gets to count all the atoms in the bond l 8 valence electrons Carbon dioxide O CO

l This shows all of the bonds. l Two double bonds, one between each oxygen and the central carbon. l Carbon dioxide O CO

More sharing examples O2O2 N2N2 O ONNOOO O NNNN NN double bond (2 pairs) triple bond (3 pairs) Share until octet is complete. octet complete

NaCl NaCl + - electron transfer and the formation of ions ionic bond This is the formation of an ionic bond. Cl Cl 2 covalent bond This is the formation of a covalent bond. sharing of a pair of electrons and the formation of molecules

ioniccovalent valence electrons Comparison of Bonding Types sharing of electrons transfer of electrons ions molecules  EN > 1.5  EN < 1.5 high mplow mp molten salts conductive non- conductive

Electronegativity (EN) - A measure of the ability of an atom in a compound to attract electrons

Electronegativity Difference: Ionic or Covalent Chlorides of Period 2 compound LiClBeCl 2 BCl 3 CCl 4 NCl 3 OCl 2 Cl 2  EN Chlorides of Period 3 Compound NaClMgCl 2 AlCl 3 SiCl 4 PCl 3 SCl 6 Cl 2  EN large differencesmall difference The electronegativity difference:  EN = EN higher – EN lower