Chemical Bonding

Chapter 6

Chemical Bond

Chemical Bond – an attraction between atoms to hold the atoms together

Review

Which type of elements are the most stable (least willing to undergo change)?

How many valence electrons do they have?

What would you expect of the other elements to increase their stability?

Octet Rule

Octet Rule- atoms gain, lose, or share electrons in order to acquire a full set of 8 valence electrons.We will address exceptions to octet rule also.

Ex. sodiumA sodium ion is more stable than the neutral sodium atom because it now has 8 valence electrons.

3 types of Bonds

Nonpolar covalent bonds- valence electrons are shared equally between bonded atoms.

Polar covalent bonds- valence electrons are shared unequally between the bonded atoms.

Ionic bonds- valence electrons are transferred from one atom to another forming ions. These oppositely charged ions attract.

Bonding between atoms is rarely purely ionic or covalent. It is usually some degree between the two.

General rule on the type of bond that forms between two atoms:

Ionic bond-a metal and a nonmetal, or a polyatomic

Covalent bond-2 or more non-metals, sharing of electrons

Electronegativity

Electronegativity Differences-Used to determine what type of bond forms (Pg. 151)0-.2 nonpolar covalent.3-1.7 polar covalent>1.7 ionic

Example: Determine the type of bond with electronegativity differences:

H and Cl: Cs and Cl: Cl and Cl:

Prac p163 and section review p163

Molecular Cmpds

Molecule (2 or more nonmetals)-a neutral group of atoms held together by covalent bondsMolecular cmpd

Molecular formula-shows the number and kind of atoms in a molecule of a compound

Diatomic molecule-molecule with only 2 atoms Ex.

Diatomic elements-element that comes as 2 atoms (Memorize:HBrONClIF)

Diagram graph on p165, show why a bond forms at position c and not at d, a.

Show the overlapping of orbitals in H2

Chemical Bonds

Bond Length – distance between 2 bonded atoms

Bond energy – energy required to break a chemical bond into isolated atoms

Electron Dot Notation

Electron Dot Notation – Element symbol represent the nucleus and electrons other than the valence electrons. The dot (s) around the symbol represent the valence electrons

Note: This is an important representation because it is mostly the valence electrons that undergo chemical rxns

Illustrate the electron dot notation for all the elements in period 2:

Lewis Structures

Lewis structures-using electron dot notation to show the way atoms form a compound

Single Bond

Single bond is the sharing of one pair of electrons between 2 atoms, represented by 2 elec dots or a dash.

Ex.

H2 HF

Single Bond

Draw these Lewis structures. Note if C is in the formula, it is the central atom.

H2O, HBr, F2, NH3, H2S, CH3I

Double Bond

Double bond – covalent bond formed by sharing two pairs of electrons b/t atoms.

Illustrate C2H4, CO2

Triple Bond

Triple bond-a covalent bond formed by sharing 3 lone pairs of electrons between two atoms.

Illustrate C2H2, N2

Multiple Bonds

Double bonds and triple bonds are called multiple bonds.

Which type of bond is the strongest? p173Weakest?Which bond is the longest?Shortest?

Practice 174

Resonance

Resonance – bonding that requires several structures to represent the molecule or ion. The actual molecule (ion) is resonating from one structure to another.

Ex. O3, CO3 -2

Section Review p175

Ionic Bond

Ionic cmpd – cmpd made up of positive and negative ions that combine to be neutral.

Formula unit – simplest repeating unit of ionic cmpd

Formation of Ionic Cmpd

Using electron dot structureEx. Na and Cl to Na+ and Cl- = NaCl

Ex. Ca and F to Ca+2 and F-1 = CaF2

Section Review p180

Ionic vs. Molecular Cmpds

1. Ionic cmpds have very strong attractions to hold the formula units together. Attractions holding molecules together is weaker.

2. Ionic cmpds have high melting pt, boiling pt, and high degree of hardness due to above reason.

3. Ionic cmpds are brittle. Illustrate reason. See p179 fig. 6-17

Polyatomic Ions

Polyatomic Ions – group of atoms bonded covalently that have a charge.

Suffix of –ate, if more oxygens

Suffix of –ite, if less oxygens

Metallic Bonding

Metallic Bonding – bonding due to attraction between metal atoms and a sea of electrons. Illustrate concept.

Malleability – metals can be hammered into sheets

Ductility – metals can be drawn into wires

Section Review p182

Molecular Geometry

VSEPR Theory = valence shell electron pair repulsion theory = valence pairs stay as far as possible from each other due to repulsion.

Illustrate and name the 8 different molecular shapes to be memorized (p186)

Practice p187

Hybridization

Hybridization – mixing of 2 or more atomic orbitals to produce new orbitals of the same energy

Ex.

Illustrate:

Polar vs. Nonpolar molecules

To determine if a molecule is polar or nonpolar:

1. Identify the shape of molecule

2. Show bond polarity with aid of electronegativity

Ex. HCl, CO2, CH4, NH3, H2O

Intermolecular Forces

Intermolecular Forces – attractions between molecules

3 types1. Dipole-Dipole – attraction between

polar molecules

Ex. Show dipole-dipole force between two molecules of NH3

2. Hydrogen Bonding – intermolecular force where hydrogen is attracted to an unshared pairs of electrons on another molecule

Illustrate with NH3 and H2O

3. London Dispersion Forces – temporary intermolecular attractions caused by motion of molecules.

Illustrate with H2 and O2

Section Review p193

Polymers

Polymers – large molecules made up of many units joined through rxns

Monomers – small units

Thermoplastic polymer – melts when heated and can be reshaped many times

Thermosetting polymer – doesn’t melt when heated but keeps its original shape

Types of Polymers

There are linear polymers, branched polymers, and cross linked polymers. See diagram p685

Types of Polymers

Addition Polymer – formed from double bonded monomers linked up.

Ex.

CH2=CH2 CH2=CH2 CH2=CH2 →

-CH2-CH2-CH2-CH2-CH2-CH2-

Condensation Polymer – formed by removing a molecule of water between two monomers

See p690 for example

Patterns of Monomers

Possible Patterns of monomers:AAAAAA

ABABAB

AAABBBAAABBB

AABBBBBBABAA