Bonding Unit Learning Goal #1: Analyze the relationship between the valence (outermost) electrons of an atom and the type of bond formed between atoms.

Electrons e-e-  Negative Charge  Mass = 1/2000 amu  Found in the Electron Shell Arranged in Energy Levels  In a neutral atom the electrons equal the protons.  Electrons are gained or lost in the formation of an ion.

Electron Shells (Energy Levels)

Review of Valence Electrons Remember : Remember : – Valence electrons are the electrons in the OUTERMOST energy level… that’s why we did all those electron configurations! B is 1s 2 2s 2 2p 1 The outer energy level is 2 B is 1s 2 2s 2 2p 1 The outer energy level is = 3 electrons These are the valence electrons! Br is [Ar] 4s 2 3d 10 4p 5 How many valence electrons are present? Br is [Ar] 4s 2 3d 10 4p 5 How many valence electrons are present?

Electron Distribution in Molecules Valence Electron distribution is depicted with Lewis (electron dot) structures Valence Electron distribution is depicted with Lewis (electron dot) structures This is how you decide how many atoms will bond covalently! (In ionic bonds, it was decided with charges) This is how you decide how many atoms will bond covalently! (In ionic bonds, it was decided with charges) G. N. Lewis

Practice

Bond Formation A bond can result from an  Interaction between valence electrons.

Chemical bonds: an attempt to fill electron shells 1.Ionic bonds 2.Covalent bonds 3.Metallic bonds

Hydrogen and Helium follow the duet rule. They fill the outer electron shell with TWO electrons. 8 Electrons

Violations of the Octet Rule Usually occurs with B and elements of higher periods. Common exceptions are: Be, B, P, S, and Xe. BF 3 SF 4 Be: 4 B: 6 P: 8 OR 10 S: 8, 10, OR 12 Xe: 8, 10, OR 12

IONIC BOND Bond formed between two ions by the transfer of electrons Metal + Nonmetal

Ionic compounds result when metals react with nonmetals Metals lose electrons to match the number of valence electrons of their nearest noble gas Positive ions form when the number of electrons are less than the number of protons Group 1 metals  ion 1+ Group 2 metals  ion 2+ Group 13 metals  ion 3+

 In ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metals  Nonmetal add electrons to achieve the octet arrangement Nonmetal ionic charge: 3-, 2-, or 1-

COVALENT BOND Bond formed by the sharing of electrons Nonmetal + Nonmetal

14, 15, 16, 17 And Hydrogen

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Molecule (O 2 ) Oxygen Molecule (O 2 )

Bonds in all the polyatomic ions and diatomics are all covalent bonds

METALLIC BOND Bond found in metals; holds metal atoms together very strongly Metal + Metal Electrons move freely around the positive nuclei of the metal atoms.

Bond and Lone Pairs Valence electrons are distributed as shared or BOND PAIRS and unshared or LONE PAIRS. Valence electrons are distributed as shared or BOND PAIRS and unshared or LONE PAIRS. HCl lone pair (LP) shared or bond pair This is called a LEWIS structure.

Steps for Building a Dot Structure Ammonia, NH 3 1.Decide on the central atom; never H. 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

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 3 pairs (6 electrons), while H shares 1 pair (2 electrons).

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

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

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?

Practice Problems

Resonance Structure A resonance structure is an alternate way of drawing a Lewis dot structure for a compound. For some molecules, there are multiple ways to draw a Lewis dot structure that still satisfy the rules

Essential Questions 1.How can a pattern in the periodic table be used to describe an element’s number of valence electrons? 2.Describe how the number of valence electrons can be used to predict the loss or gain of the electrons and the subsequent charge on the resulting ion.