IN: 1/7/16 Discuss the following questions while we wait for the bell: –What holds atoms together in an ionic bond? –Why do atoms form ions?

Covalent Bonding Bonding models for methane, CH 4. Models are NOT reality. Each has its own strengths and limitations.

Standards  Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds.  Students know chemical bonds between atoms in molecules such as H 2, CH 4, NH 3, H 2 CCH 2, N 2, Cl 2, and many large biological molecules are covalent.  Students know how to draw Lewis dot structures.  Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds.  Students know chemical bonds between atoms in molecules such as H 2, CH 4, NH 3, H 2 CCH 2, N 2, Cl 2, and many large biological molecules are covalent.  Students know how to draw Lewis dot structures.

The Octet Rule and Covalent Compounds  Covalent compounds tend to form so that each atom, by sharing electrons, has an octet of electrons in its highest occupied energy level.  Different from ionic compounds that transfer electrons to achieve a full octet

The Octet Rule: The Diatomic Fluorine Molecule F F 1s 2s 2p seven Each has seven valence electrons FF

The Octet Rule: The Diatomic Oxygen Molecule O O 1s 2s 2p six Each has six valence electrons O O

The Octet Rule: The Diatomic Nitrogen Molecule N N 1s 2s 2p five Each has five valence electrons N N

Concept Review In your notes, draw a sketch to remind you of the difference between ionic and covalent bonds

BONDING IN COVALENT MOLECULES Atoms share electrons to obtain a stable, octet (or duet) arrangements Water (H 2 O) H... O :. H.. H – O : H ← LONE PAIR ← BONDING PAIR LEWIS STRUCTURE – A diagram using electron dot notation to show how the valence electrons are arranged among bonded atoms 3B-16

To draw a proper Lewis Structure: 1 – Add up the valence e - s for all of the atoms in the molecule or ion 2 – Draw a skeletal structure by using pairs of electrons to make bonds 4 – If octets are not produced, make the atoms that have octets share more e - pairs with atoms that do not have octets 3 – Complete octets (or duets for H) for all atoms, outer atoms first, using the remaining valence e - s 3B-17

Predicting the Location of Certain Atoms Hydrogen is always on the outside because it can only share one pair of electrons Hydrogen is always on the outside because it can only share one pair of electrons The least electronegative atom is normally the central atom. The least electronegative atom is normally the central atom.

Sulfur dichloride, SCl = 20 valence e - s Cl S Cl 3B-18

Ammonia, NH = 8 valence e - s H N H H 3B-20

IN: 1/12/16 What is a Lewis structure? What is a Lewis structure? What steps do we use to write Lewis structures? What steps do we use to write Lewis structures?

Fluorine, F = 14 valence e - s F SINGLE BOND – One shared pair of e - s between two atoms 3B-22

Oxygen, O = 12 valence e - s O DOUBLE BOND – Two shared pairs of e - s between two atoms 3B-23

Nitrogen, N = 10 valence e - s N TRIPLE BOND – Three shared pairs of e - s between two atoms 3B-24

Other Diatomic Molecules Hydrogen Hydrogen Nitrogen Nitrogen Oxygen Oxygen Fluorine Fluorine Chlorine Chlorine Bromine Bromine Iodine Iodine

Hydrogen cyanide, HCN = 10 valence e - s H C N Carbon disulfide, CS 2 3B-25

Practice Worksheet

Welcome 1/13/15 Take out your notes and your practice worksheet Take out your notes and your practice worksheet With your neighbor, review the steps for drawing lewis structures and the practice problems we went through yesterday while we wait for the bell With your neighbor, review the steps for drawing lewis structures and the practice problems we went through yesterday while we wait for the bell

Sulfate, SO (6) O O S O O + 2 = 32 valence e - s 2- Ammonium, NH 4 + H H N H H 5 + 4(1)- 1 = 8 valence e - s + 3B-26

Ozone, O = 18 valence e - s O O O or O O O ↔ RESONANCE – When more than one Lewis structure can be drawn for a molecule or ion RESONANCE STRUCTURES – The Lewis structures that can be drawn for the molecule or ion The real ozone molecule is a average of its resonance structures 3B-27

Resonance Occurs when more than one valid Lewis structure can be written for a particular molecule. These are resonance structures. The actual structure is an average of the resonance structures.

Resonance in Benzene, C 6 H 6

Draw the resonance structures for the nitrate ion NO 3 -1

Draw the resonance structure for the formate ion CHO 2 1-

Bond Length and Bond Energy

Whiteboard Practice: Draw the following Lewis structures PBr 3 N 2 H 2 NO 2 -1 C 2 H 4

Whiteboard Practice: Draw the following Lewis structures HBr C 2 H 5 OH N 2 F 4

Whiteboard Practice PH 3 SO 2

Quiz CS 2 SO 4 2- C 2 H 2 HCN PBr 3