Bond Types

Let’s Look At 3 Types of Bonds

• Ionic• Polar Covalent (Molecular)• Nonpolar Covalent

(Molecular)

Remember Electronegativity?

• The tendency for an atom to attract electrons to itself in a bond– The higher the value, the better it is at

attracting electrons.• The difference in the

electronegativity values determines what type of bond will be formed.

ElectronegativityElectronegativityElectronegativity is a scale from 0.7 (Cs) to 4.0 (F).

Electronegativity generally increases across a period and decreases down a group.

Electronegativity Values (these will be given to you)

• Why don’t the noble gases have a value?

• They don’t attract electrons!

Ionic Bonds

• If the electronegativity difference is greater than 1.7, one atom will pull the electron completely away from other atom.

• The electrons are NOT shared.• An Ionic BondIonic Bond is formed as + and – attract.• Electronegativity of Na is 0.9; Cl is 3.0.• 3.0 – 0.9 = 2.1; difference >1.7, so…Ionic!

Polar Covalent Bonds

• Covalent bonds share electrons• The shared pairs are pulled, similar to a

tug-of-war, between the nuclei of the atoms sharing the electrons.

• If the electronegativity difference is between 0.3 – 1.7, one side of the bond becomes slightly more negative and the other side becomes slightly more positive.

• This is a PolarPolar Covalent BondCovalent Bond.

Polar Covalent Bonds

• The electronegativity of H is 2.1; Cl is 3.0.• 3.0 – 2.1 = 0.9; difference is b/w 0.3 – 1.7, so…

Polar Covalent!

ClH∂+ ∂-

Slightly

Polar Covalent Bonds

• The electronegativity of O is 3.5; H is 2.1.• 3.5 – 2.1 = 1.4• Difference is b/w 0.3– 1.7, so… Polar Covalent!

Nonpolar Covalent Bonds• When the atoms have equal pull, causing the

electrons to be equally shared, the bond is Nonpolar CovalentNonpolar Covalent.

• Neither side of the bond is even slightly positive or negative.

• The electronegativity difference is b/w 0.0 – 0.3. • This is the type of bond that occurs between 2

atoms of the same element. (H2, O2, Cl2, etc.)

Nonpolar Covalent Bonds

• The electronegativity of H is 2.1.

• 2.1 – 2.1 = 0

• The difference is b/w 0.0 – 0.3, so…Nonpolar!

3 Different Types of Bonds

LewisLewis DotDot

StructuresStructures

IonicIonic & Metallic Bonding& Metallic Bonding

And…And…

Valence ElectronsValence ElectronsElectrons in the outer energy level.Electrons in the outer energy level.Determine chemical and physical Determine chemical and physical

properties of an elementproperties of an elementThe group number of the representative The group number of the representative

elements is the elements is the samesame as the number of as the number of valence electrons.valence electrons.

All of the elements within a given group All of the elements within a given group will have the same number of valence will have the same number of valence electrons.electrons.

For example:For example: Be is in Group 2A.Be is in Group 2A.There are 2 electrons in the There are 2 electrons in the

outermost energy level. outermost energy level. Be has an eBe has an e configuration of 1s² 2s² configuration of 1s² 2s²How many valence electrons will F How many valence electrons will F

have?have?

ValenceValence ElectronsElectrons

7

Lewis Dot Diagrams and the Octet Rule

•Noble gases have a FULL valence shell of 8 electrons (ns2np6).

•(Helium has a full valence shell with only 2 valence electrons.)

•Through bonding, other atoms “seek” a full shell of eight electrons.

•This is called the OCTET RULE.•Noble gases are unreactive (inert) because they already have a full shell!

Valence ElectronsValence Electrons

Lewis Dot Diagrams and the Octet Rule

•A visual representation of where the bonding electrons are in an atom

•The VALENCE electrons are shown as dots around the symbol for the element.

•This is called an electron dot diagram or a Lewis dot structure.

Electron Dot DiagramsElectron Dot Diagrams

HOW TO MAKE A DOT DIAGRAMHOW TO MAKE A DOT DIAGRAM Write the symbol for the element. Write the symbol for the element. Decide how many valence electrons the Decide how many valence electrons the

element has.element has. Using dots, place one dot per electron on Using dots, place one dot per electron on

each side of an imaginary box around the each side of an imaginary box around the symbol.symbol.

You must place one dot on each side of the You must place one dot on each side of the box before doubling up.box before doubling up. Otherwise, the order doesn’t matter.Otherwise, the order doesn’t matter.

N

5

N

ElectronElectron DotDot DiagramsDiagrams

Lithium has only 1 valence electron, so we Lithium has only 1 valence electron, so we only place one dot on our diagram. only place one dot on our diagram.

LithiumLithium

LiLi

1 valence electron!1 valence electron!

ElectronElectron DotDot DiagramsDiagrams

Beryllium has 2 valence electrons, so we Beryllium has 2 valence electrons, so we place two dots on our diagram. place two dots on our diagram.

BerylliumBeryllium

BeBe

BeBe

IonicIonic BondingBonding An atom is always trying to get a full outer An atom is always trying to get a full outer

energy level of eight electrons—Octet Rule.energy level of eight electrons—Octet Rule.

Atoms can gain, lose, or share valence (outer) Atoms can gain, lose, or share valence (outer) electrons to complete their outer shell.electrons to complete their outer shell.

When atoms get their full shells by completely When atoms get their full shells by completely giving or taking electrons from other atoms, an giving or taking electrons from other atoms, an Ionic Bond Ionic Bond is formedis formed..

IonicIonic BondingBonding Involves Involves

A metal and a nonmetalA metal and a nonmetal• A positively charged ion ( A positively charged ion ( the metalthe metal) ) • A negatively charged ion (A negatively charged ion (the nonmetalthe nonmetal))

An electrostatic attraction happens!An electrostatic attraction happens!• (One atom loses an electron, the other (One atom loses an electron, the other

gains it. They become oppositely charged gains it. They become oppositely charged ““bondbond”” together!) together!)

IonicIonic BondingBonding Are these pairs likely to form ionic Are these pairs likely to form ionic

compounds?compounds? Cl, BrCl, Br

K, He K, He

Na, ClNa, Cl

No—Both nonmetals that form negative ions.

No—Helium is a noble gas that doesn’t bond with anything.

Yes—Sodium is a metal that forms a positive ion, and chlorine is a nonmetal that forms a negative ion.

IonicIonic BondingBonding

Na Cl+ -

Two ions now Two ions now stuck together!stuck together!

NaCl

4 Properties4 Properties ofof IonicIonic CompoundsCompounds1.1. At room temp. most ionic compounds are a At room temp. most ionic compounds are a

crystalline solidcrystalline solid2.2. Ionic compounds are Ionic compounds are brittlebrittle and shatter if hit and shatter if hit

Ions of like charge are forced near each Ions of like charge are forced near each other.other.

3.3. Because of the strong electrostatic attractions, Because of the strong electrostatic attractions, crystalline solids are crystalline solids are very stablevery stable and have high and have high melting points!melting points!

4.4. When melted or dissolved, ionic compounds When melted or dissolved, ionic compounds can can conduct electricityconduct electricity!!

All of the charged All of the charged particles (ions) particles (ions) enable a flow of enable a flow of current.current.

SaltSalt waterwater

SugarSugar waterwater

Metallic BondingMetallic Bonding

The mobile valence electrons make them The mobile valence electrons make them good good conductors conductors of heat and electricity!of heat and electricity!

Metals are made of closely packed cations with Metals are made of closely packed cations with mobile “de-localized” valence electrons.mobile “de-localized” valence electrons.

The attraction of The attraction of the free-floating the free-floating valence electrons valence electrons for the positively for the positively charged metal charged metal ions forms the ions forms the metallic bond.metallic bond.

Attractions Between MoleculesVan der Waals ForcesVan der Waals Forces

• Weaker than either the ionic or covalent bonds that form between atoms in a compound.

• Responsible for determining whether a compound is a liquid, gas, or solid

• 3 basic types from weakest to strongest– (London) Dispersion forces– Dipole interaction– Hydrogen bonding

London Dispersion Forces

• Weakest of all molecular attractions• Caused by the motion of electrons producing

a temporary polarity.• Strength of dispersion forces generally

increases as # of electrons in the molecule increases.

• All molecules have these weak attractions.

London Dispersion Forces

Dipole Interaction

• Occurs when polar molecules are attracted to one another

Hydrogen Bonds

• Occurs b/w molecules in which H is covalently bonded to either O, N, or F, which are very electronegative– Causes very polar molecules that are

strongly attracted to each other– Still only has about 5% of the strength

of a covalent bond

Hydrogen BondsVery Important!!• Reason ice is

less dense than water

• Reason for the relatively high b.p. of water

• Responsible for the double helix of the DNA molecule

O

H H

HH

O

+

+

2 lone pairs

Nonpolar or Polar MoleculesMolecules

• We now know how to determine if the bond b/w atom and atom in a compound is polar or nonpolar.

• But…what about the whole molecule?

Nonpolar or Polar MoleculesMolecules

• Draw the Lewis Structure. • If the central atom has any unshared pairs,

the molecule is polar.

Nonpolar or Polar MoleculesMolecules

• If there are no unshared pairs on the central atom, look at the atoms around the central atom.– If they are all the same, the molecule is nonpolar.– If any one of them is different, the molecule is

polar. • In a 2-atom molecule, if the bond between the 2

atoms is polar then the whole molecule is polar.

Nonpolar or Polar MoleculesMolecules

H2O

CO2

HCN

CH3Cl

Polar

Nonpolar

Polar

Polar

N2Nonpolar

HCl

Polar

MalleableMalleable – able to be – able to be pounded into sheets. pounded into sheets. Metals do not shatter as Metals do not shatter as

mobile electrons keep mobile electrons keep the positive metal ions the positive metal ions from getting too close to from getting too close to each other.each other.

DuctileDuctile – able to be – able to be drawn into wiresdrawn into wires