Concepts of Chemical Bonding Chapter 12 – Basic Concepts Chapter 13 – Molecular Structure Chapter 14 – Polarity

Salt vs. Sugar

Salt vs. Sugar  Night and Day ► Salt  Ionic compound  Na + and Cl -  Held together by opposite charges (ionic bond)  An electrolyte (will conduct electrical current when dissolved in solution) ► Sugar (sucrose)  Covalent compound  C 12 H 22 O 11  Atoms share electrons and are held together by covalent bonds  A non-electrolyte (will NOT conduct an electrical current when dissolved in solution)

Two Things You Should Always Remember: ► Atoms bond with other atoms to complete their outer energy levels  become stable. ► The properties of substances are determined in large part by the chemical bonds that hold atoms together.

Types of Bonding ► Chemical bond – forms when atoms or ions are strongly attracted to one another. There are three basic types: 1) Ionic bond 2) Covalent bond 3) Metallic bond

Valence electrons are the outer shell electrons of an atom. The valence electrons are the electrons that participate in chemical bonding. 1A 1ns 1 2A 2ns 2 3A 3ns 2 np 1 4A 4ns 2 np 2 5A 5ns 2 np 3 6A 6ns 2 np 4 7A 7ns 2 np 5 Group# of valence e - e - configuration

Lewis Dot Structures ► Includes chemical symbol of element, plus dots for each valence electron. Try 1) Li 2) O 3) Ar

The Octet Rule ► We last stated: atoms that have eight valence electrons are chemically stable. ► Related to bonding: atoms will gain, lose, or share valence electrons until they are surrounded by eight valence electrons. ► For the exceptions on table: atoms will gain, lose or share valence electrons to achieve the same number of electrons as the noble gas closest to them on the periodic table.

Li + F Li + F - The Ionic Bond 1s 2 2s 1 1s 2 2s 2 2p 5 [He][Ne] Li Li + + e - e - + FF - F - Li + + Li + F - The actual bond  attraction of opposite charges.

Ionic Bonding ► Use Lewis dot symbols to show the formation of NaCl.

Ionic Bonding ► Use Lewis dot symbols to show the formation of aluminum oxide.

A covalent bond is a chemical bond in which two or more electrons are shared by two atoms. Why should two atoms share electrons? FF + 7e - FF 8e - F F F F Structure of F 2 lone pairs single covalent bond 9.4

Covalent Bonding ► H 2, HCl, H 2 O, NH 3, and CH 4 ► Lewis Structures – shared electron pairs are shown as lines; unshared electron pairs are shown as dots.

8e - H H O ++ O HH O HHor 2e - Lewis structure of water Double bond – two atoms share two pairs of electrons single covalent bonds O C O or O C O 8e - double bonds Triple bond – two atoms share three pairs of electrons N N 8e - N N triple bond or 9.4

Bond Type Bond Length (pm) C-CC-CC-CC-C154 CCCCCCCC133 CCCCCCCC120 C-NC-NC-NC-N143 CNCNCNCN138 CNCNCNCN116 Lengths of Covalent Bonds Bond Lengths Triple bond < Double Bond < Single Bond 9.4

Ionic vs. Covalent Compounds ► Ionic  High melting points  Conduct electricity in molten state or when dissolved in solution  Tend to be soluble in water  Usually crystallize as sharply defined particles.  Usually solid at room temp.

More Ionic...

Covalent Properties ► Covalent  Low melting points  Do not conduct electricity  Not very soluble in water  Usually liquid or gas at room temperature. Some are low-melting solids.

► Covalent Bonds ► Bond Axis ► Bond Angle ► Bond length  NOT FIXED

Covalent Bond Length ► Bond length measurements are average measurements because the molecules undergo a variety of motions. (they have energy) ► Symmetric stretching (same direction) ► Asymmetric stretching (opp. direction) ► Bending (opp. Direction) ► Rotating (wagging) {same direction}

Get up and do the MOLECULE DANCE!! in/MoleculeHTML/H2O_html/H2O_ page.html in/MoleculeHTML/H2O_html/H2O_ page.html

How do you know what type of bond will form???

Electronegativity ► The ability of an atom in a molecule to attract electrons to itself. A tug of war for those shared electrons!!

► A highly electronegative atom will really attract electrons toward itself.  High electron affinity  High ionization energy ► Yes, there is a trend!!!!

F – F

N – O

Rb – F

Which is Which?

Classify the following bonds as ionic, polar covalent, or covalent: The bond in CsCl; the bond in H 2 S; and the NN bond in H 2 NNH 2. Cs – 0.7Cl – – 0.7 = 2.3Ionic H – 2.1S – – 2.1 = 0.4Polar Covalent N – – 3.0 = 0Covalent 9.5

Most Ionic; Most Covalent? Which of the following bonds is the most ionic? Li-O, Na-O, K-O, Rb-O, Cs-O Which of the following bonds is the most covalent? Li-O, Na-O, K-O, Rb-O, Cs-O

Metallic Bonding ► Form between metal atoms ► Metals hold on to their valence electrons weakly. ► Think of them as positive ions floating in a sea of electrons. ► The negative ‘cloud’ covers the positive charges forming a ‘glue’ that hold the metal together.

Metallic Bonding

► A. Outermost electrons wander freely through metal. Metal consists of cations held together by negatively-charged electron "glue." ► B. Free electrons can move rapidly in response to electric fields, hence metals are a good conductor of electricity. ► C. Free electrons can transmit kinetic energy rapidly, hence metals are good conductors of heat. ► D. The layers of atoms in metal are hard to pull apart because of the electrons holding them together, hence metals are tough. But individual atoms are not held to any other specific atoms, hence atoms slip easily past one another. Thus metals are ductile. Metallic Bonding is the basis of our industrial civilization.