Covalent BondsCovalent BondsBonding of nonmetal to

nonmetal.

All elements want to gain electrons, so they must

SHARE valence electrons. Study your ion chart everyday!! Quiz this

Friday!

A.6 Chemical Bonding

It’s a lot like dogs…

ATOMIC STRUCTURE

HELIUM ATOM NEON ATOM

Label the protons, neutrons, and electrons in their correct locations on the diagrams below.

This first shell surrounding the nucleus can hold ________ electrons and the second shell can hold ________ electrons.

Where are the valence electrons??

ELECTRON-DOT DIAGRAMS

The valence electrons of an atom can be written in the following way, where the electrons are represented by dots around the chemical symbol of the element.

Imagine that you are writing the dots on a square around the chemical symbol.

Atomic Structure

  

NAME SYMBOL ATOMIC NUMBER NUMBER OF ELECTRONS IN OUTERMOST

ENERGY LEVEL

ELECTRON DOT FORMULA

HYDROGEN

H 1 1 H•

LITHIUM

BORON

NEON

FLUORINE

Why do atoms bond together?

• Atoms bond together to become more like Noble Gases in electron arrangement.

• Bonding produces new substances.

• Involves only the 'outer shell' or 'valence' electrons

stablestable

Atoms can bond in several ways …

• COVALENT BONDING – sharing electrons to form molecules withcovalent bonds

– formed between two nonmetals in a molecule.

• IONIC BONDING - By one atom transferring electrons to another atom.

Covalent and Ionic Bonding

Covalent Bonding• Example 1: 2 hydrogen atoms (1) form the molecule of the element hydrogen H2

Two hydrogen atoms with their valence electrons.

How many electrons would make these atoms stable? Both atoms need one electron to

fill their outer valence level, so they SHARE an electron.

Now they both have 2 electrons in the outer energy level.

Covalent Bonding• Example: 2 atoms of hydrogen (1) combine

with 1 atom of oxygen to form water H2O  

HH22OO

Molecular shapes determine the chemical and physical properties

like boiling point and viscosityVSEPR Model

– Valence Shell Electron Pair Repulsionspecific bond angles are formed between terminal and central atoms.

Lone pairs of electrons occupy a slightly larger orbital and “push” shared electron bonding orbitals together.

Molecular Shapese-pairs

Notation Name of VSEPR shape

Examples

2 AX2 Linear HgCl2 , ZnI2 , CS2 , CO2

3 AX3 Trigonal planar

BF3 , GaI3

AX2E Non-linear (Bent)

SO2 , SnCl2

4 AX4 Tetrahedral

CCl4 , CH4 , BF4-

AX3E (Trigonal) Pyramidal

NH3 , OH3-

AX2E2 Non-Linear (Bent)

H2O , SeCl2

5 AX5 Trigonal bipyramidal

PCl5 , PF5

AX4E Distorted tetrahedral (see-sawed)

TeCl4 , SF4

AX3E2 T-Shaped

ClF3 , BrF3

AX2E3 Linear I3- , ICl2

-

6 AX6 Octahedral

SF6 , PF6-

AX5E Square Pyramidal

IF5 , BrF5

AX4E2 Square Planar

ICl4- , BrF4

-

Bond Polarity and ElectronegativityBond Polarity and Electronegativity

Electronegativity and Bond Polarity• There is no sharp distinction between bonding types.• The positive end (or pole) in a polar bond is represented

+ and the negative pole -.

Electronegativity: measure of the tendency for an atom to attract bonding electrons

Trends: increases left to right within period and from bottom to top within group.

covalent bonds revisited

• in a covalent bond between atoms with same electronegativity, there is “equal” probability of finding electrons around either bonded nucleus.

• in a polar covalent bond the more electronegative atom gains partial (-) charge, and the less electronegative atom gains partial (+) charge. This partial charge separation gives rise to “dipoles”.

“polar” vs. “non-polar” molecules

• A molecule is considered “polar” if it has a net “dipole moment”. A molecule is “non-polar” if it has no net dipole moment (or if the dipole moment is negligibly small)

• Characteristics of a polar molecule: – Polar covalent bond(s)– Molecular geometry that gives rise to a net dipole moment

Intermolecular forces

Van der Waals Forces

Intramolecular vs. Intermolecular Forces

Intramolecular Forces

Intermolecular Forces

Intramolecular vs. Intermolecular Forces (IMFs)

STRONGER

WEAKER

Dispersion forceWeakest Intermolecular Force (IMFs)

• Present in all atoms and molecules.

• The random movement of electrons will sometimes result in their unequal distribution. – One area of the atom then

becomes more negatively charged and one more positively charged.

• Element with more electrons have stronger dispersion forces since they have more charge.– Halogen family: explains why F & Cl

are gases. Br is liquid. I & At are solid.

Dispersion forces increase as atom size increases.

Dispersion forceWeakest Intermolecular Force

Dipole-Dipole Forces (IMFs)

Attractions between oppositely charged regions of polar

molecules

http://www.elmhurst.edu/~chm/vchembook/160Aintermolec.html

Intermolecular Forces (IMFs)

Hydrogen Bonding

Special Type of dipole-dipole attraction between molecules containing:

• a hydrogen atom (H)• a small, highly electronegative

atom (N,O,F)• at least one lone pairOf electrons

http://library.thinkquest.org/28751/review/biochem/2.html

Complete the Chart:Intermolecular Forces

(IMFs) Dispersion Dipole-dipole

HydrogenRelativeStrength

How it’sFormed

Molecular Examples

Identifying Intermolecular Forces

What type of intermolecular forces must be overcome to:

a. Melt ice?b. Boil water?c. Melt NaCl?d. Sublime I2

Intermolecular Forces

Which of the following compounds can form dipole-dipole forces?

Cl2

CONOCH4

States of Matter &Intermolecular Forces

Focus on the following criteria:How the Strengths of forces between molecules

Affect the properties of gases, liquids and solids

(like viscosity, melting point, and boiling point)

**Emphasize dispersion, dipole-dipole, & hydrogen IMFs

Hydrocarbons:Hydrocarbons:PetroleumPetroleum

Phase Changes, IMFs, & Phase Changes, IMFs, & NamingNaming

Chapter Chapter

21.1-21.421.1-21.4

Provides ½ of US energy needs for transportation, heat, & electricity

Provides raw materials for manufactured products

What is Petroleum used for?

Crude oil is a mixture of hydrocarbons

What is in petroleum?

Who has the oil? Who uses it? Where is it found?

How is crude oil separated?

Fractional Fractional DistillationDistillation separates distinct mixtures from crude oil.

Fractions

Lowest bp = WEAK intermolecular forces

highest bp = STRONG intermolecular forces

Separation by Distillation

Separation by Distillation

• Liquid mixtures can be separated by their boiling points (bp).

• Every substance has it own specific bp.

• When a substance is undergoing a phase change, its temperature stays the same.

2-propanol

H2O

Boiling Point/

Condensation Point

Freezing point/

Melting point

Phase Change Graph

Time

•The horizontal parts of the graph represent the temperatures at which a phase change will occur.

•All substances have their own specific melting and boiling points.

Examining Petroleum’s Molecules

Intermolecular Forces are BETWEEN molecules

Lowest bp = weak intermolecular forces = small hydrocarbons

Highest bp = strong intermolecular forces = large hydrocarbons

Examples:

Butane

Nonene

decyne

2-methylbutane