IIIIIIIV Chemical Bonding I. Introduction to Bonding

A. Vocabulary zChemical Bond yattractive force between atoms or ions that binds them together as a unit

IONIC COVALENT Bond Formation Type of Structure Solubility in Water Electrical Conductivity Other Properties e - are transferred from metal to nonmetal high yes (solution or liquid) yes e - are shared between two nonmetals low no usually not Melting Point crystal lattice true molecules B. Types of Bonds Physical State solid liquid or gas odorous

“electron sea” METALLIC Bond Formation Type of Structure Solubility in Water Electrical Conductivity Other Properties Melting Point B. Types of Bonds Physical State e - are delocalized among metal atoms very high yes (any form) no malleable, ductile, lustrous solid

Ionic Bonding - Crystal Lattice RETURN B. Types of Bonds yRemember: Opposites Attract!

Covalent Bonding - True Molecules RETURN B. Types of Bonds Diatomic Molecule

Metallic Bonding - “Electron Sea” RETURN B. Types of Bonds

C. Bond Polarity zDifference in electronegativity determines bond type. yAbove 1.7 = ionic y = polar covalent y0-0.3 = non-polar covalent

C. Bond Polarity zElectronegativity yAttraction an atom has for a shared pair of electrons. yhigher e - neg atom has a partial negative charge   - ylower e - neg atom has a partial positive charge   +

zNonpolar Covalent Bond ye - are shared equally yusually between identical atoms Ex. F 2 C. Bond Polarity

++ -- zPolar Covalent Bond ye - are shared unequally yresults in partial charges (dipole)

zNonpolar zPolar zIonic View Bonding Animations.Bonding Animations C. Bond Polarity

Examples: zCl 2 zHCl zNaCl =0.0 Nonpolar =0.9 Polar =2.1 Ionic

D. Lewis Structures zElectron Dot Diagrams yshow valence e - as dots yEX: oxygen 2s2p O X

D. Lewis Structures zCovalent – show sharing of e - zIonic – show transfer of e -

D. Lewis Structures zCovalent – show sharing of e - zIonic – show transfer of e -

++ -- ++ D. Lewis Structures zNonpolar Covalent - no charges zPolar Covalent - partial charges

18 Steps for Building a Dot Structure Ammonia, NH 3 1. Decide on the central atom; never H. Why? If there is a choice, the central atom is atom of lowest affinity for electrons. (Most of the time, this is the least electronegative. Therefore, N is central on this one If there is a choice, the central atom is atom of lowest affinity for electrons. (Most of the time, this is the least electronegative.) Therefore, N is central on this one 2. Add up the number of valence electrons that can be used. H = 1 and N = 5 H = 1 and N = 5 Total = (3 x 1) + 5 Total = (3 x 1) + 5 = 8 electrons / 4 pairs = 8 electrons / 4 pairs

19 3.Form a single bond between the central atom and each surrounding atom (each bond takes 2 electrons!) H H H N Building a Dot Structure H H H N 4.Remaining electrons form LONE PAIRS to complete the octet as needed (or duet in the case of H). 3 BOND PAIRS and 1 LONE PAIR. Note that N has a share in 4 pairs (8 electrons), while H shares 1 pair.

20 5.Check to make sure there are 8 electrons around each atom except H. H should only have 2 electrons. This includes SHARED pairs. Building a Dot Structure 6. Also, check the number of electrons in your drawing with the number of electrons from step 2. If you have more electrons in the drawing than in step 2, you must make double or triple bonds. If you have less electrons in the drawing than in step 2, you made a mistake! H H H N

21 Carbon Dioxide, CO 2 1. Central atom = 2. Valence electrons = 3. Form bonds. 4. Place lone pairs on outer atoms. This leaves 12 electrons (6 pair). 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2. C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons

22 Carbon Dioxide, CO 2 6. There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each atom and replaced with another bond. C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons How many are in the drawing?

23 Double and even triple bonds are commonly observed for C, N, P, O, and S H 2 CO SO 3 C2F4C2F4C2F4C2F4

24 Now You Try One! Draw Sulfur Dioxide, SO 2