Bonding

K Warne

ClH X

+ -

Bonding

Objectives: At the end of this unit you should be able to:-

Explain how metallic bonding determines the prosperities of metals

State/explain (understand) the significance of valence electrons

State the conditions for covalent bonding. Explain the properties of substances (simple and giant

covalent) in terms of their bonding and structure. Know (state) conditions for ionic bonding. Name chemical compounds correctly. List the characteristics of different states of matter.

Covalent bond

A shared PAIR of electrons. Formed between ......................... Common Ions KNOW formulae; eg sulphate ion SO4

2-

Diatomic Molecules; ....2, ....2, ....2, ....2, ....2, .....2, ......2, Pure covalent bonds have .....................SHARING of the

electrons.

In covalent substances all the electrons are strongly held in the bonds and so the substance ............................ conduct electricity.

H •

Single hydrogen atomHydrogen molecule

A shared pair of electrons = a single covalent bond

Covalent bond

A shared PAIR of electrons. Formed between non metals. Common Ions KNOW formulae; eg sulphate ion SO4

2-

Diatomic Molecules; H2, O2, F2, Cl2, Br2, I2, N2, Pure covalent bonds have EQUAL SHARING of the

electrons.

H H

In covalent substances all the electrons are strongly held in the bonds and so the substance will NOT conduct electricity.

H x H•H •

Single hydrogen atomHydrogen molecule

A shared pair of electrons = a single covalent bond

This is a PURE COVALENT, SINGLE BOND!

O x

xxx

xx

O x

x

xx

xx

O x

xxx

xx

O x

x

xx

xx

O xx

xx

xx

Ox

xx

x xx

“Dot Cross Diagrams” - Lewis & Couper Notation

Lewis Diagrams

O OCouper Notation

Chemical Formulae

OName: Oxygen

Multiple Bonds: Two atoms can share more than one pair of electrons.

Draw similar diagrams for all the other diatomic molecules.

O x

xxx

xx

O x

x

xx

xx

O x

xxx

xx

O x

x

xx

xx

O xx

xx

xx

Ox

xx

x xx

“Dot Cross Diagrams” - Lewis & Couper Notation

Lewis Diagrams

O=OCouper Notation

Chemical Formulae

O2

Name:Oxygen

Multiple Bonds: Two atoms can share more than one pair of electrons.

Nitrogen (N2) has a triple bond draw Lewis & Couper diagrams for nitrogen.

Draw similar diagrams for all the other diatomic molecules.

N2

N2

Diatomic Molecules F2, Cl2, Br2,

Diatomic Molecules F2, Cl2, Br2,

Covalent Molecules CH4, H2O, NH3, CO2, NH4

+,

Covalent Molecules CH4, H2O, NH3, CO2, NH4

+,

O●

●●●

●

●x

x+

HH H+

O●

●●●

●

●x

x+ O

●●

●●

●

●x

x

+

HH H+

HH H

Methane - CH4

All the bonds are identical and the molecule has a TETRAHEDRAL SHAPE

Fluorine oxide (OF2 )

OX

X

XX

X

XF

Fluorine atom Oxygen atom

F

F

OX

X

XX

X

X

Fluorine oxide (OF2 )

F

F

O

By sharing pairs of electrons all bonding atoms now effectively have

a full outer shell (8 electrons).

OX

X

XX

X

XF

Lewis structure Couper Structure

Fluorine atom Oxygen atom

Boron tri fluoride (BF3)

Boron tri fluoride (BF3)

F

F

B

By sharing pairs of electrons all bonding atoms now effectively have a full outer shell (8 electrons).

Three shared pairs

Trigonal Planar structure

BX

XXF

F

F

F

Cl

Cl

PX

X

X

X

X Cl

F

F

S

F

F

F

F

H C N

OxH xx

xx

x

ClSx x

xxx

x

O

O

SOO

Two double bonds

Two double bonds

SO2 Lewis structure SO2 Couper structure

Be FxF x Be FF

Two shared pairs

Linear shape

Triple bonds

Triple bonds

Co-ordinate bonding

Co-ordinate or Dative covalent bonding

Co-ordinate bonding

Co-ordinate or Dative covalent bonding

Lewis acid & base

Try and draw the other two and identify the coordinate bonds.

H3NBF3 Cu(NH3)4+

Cu(H2O)62+

Lewis acid & base

Try and draw the other two and identify the coordinate bonds.

H3NBF3 Cu(NH3)4+

Cu(H2O)62+

Cu

Cu(NH3)4+

Electronegativity

The ability/power to attract electrons in a bond.

Electronegativity in a Group

H

Li

Na

Group 1Electronegativity

…………………

from TOP to BOTTOM in a group

as the number of ………… increase

bonding electrons (outer) are …………

from nucleus

and therefore ………… strongly

attracted. Ele

ctro

nega

tivity

DE

CR

EA

SE

S

Electronegativity in a Group

H

Li

Na

Group 1Electronegativity

DECREASES

from TOP to BOTTOM in a

group

as the number of shells increase

bonding electrons (outer) are further

from nucleus

and therefore LESS strongly

attracted.

Ele

ctro

nega

tivity

DE

CR

EA

SE

S

Electronegativity Trends

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

Electronegativity ………………..from LEFT to RIGHT as the number of protons in the nucleus …………………….and bonding electrons (outer) are more strongly attracted.

Group 1 2 3 4 5 6 7 8

Electronegativity DECREASES from TOP to BOTTOM in a group as the number of shells increase bonding electrons (outer) are LESS strongly attracted.

Electronegativity Trends

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

Electronegativity INCREASES from LEFT to RIGHT as the number of protons in the nucleus INCREASES and bonding electrons (outer) are more strongly attracted.

Group 1 2 3 4 5 6 7 8

Electronegativity DECREASES from TOP to BOTTOM in a group as the number of shells increase bonding electrons (outer) are LESS strongly attracted.

Electronegativity

VALENCY – BOHR DIAGRAMS

Valency – ……………….. of electrons ……..….. or ……….... to have a FULL valence level. (Outer shell)

H He

Li Be B C N O F Ne

Valence electrons – those in ……………. shell.

Na Mg Al Si P S Cl Ar

VALENCY – Bonds Formed

Valency – number of electrons lost or gained to have a FULL valence level. (Outer shell) = number of bonds formed by an element.

H He

Li Be B C N O F Ne

Valence electrons – those in outer shell = group number.

METALS NON - METALS

Polar Covalent BondEach side of the molecule has a small charge due to the electrons being …………………………..SHARED.

Chlorine has a …………………..electro negativity than hydrogen. The “” symbol (delta) stands for small amount or small change.

> This type of bonding exists when there is a relatively large …………………….. in electronegativity between the bonding atoms.

A ……………(two poles) has been created.

Electron density diagram - more electron density around the chlorine

-ClH X

+

Polar Covalent BondEach side of the molecule has a small charge due to the electrons being UNEQUALLY SHARED.

Chlorine has a higher electro negativity than hydrogen. The “” symbol (delta) stands for small amount or small change.

> This type of bonding exists when there is a relatively large difference in electronegativity between the bonding atoms.

A dipole (two poles) has been created.

Electron density diagram - more electron density around the chlorine

-ClH X

+

Bond Polarity in Water

The oxygen atom has ………... electronegativity so it attracts the electrons more strongly than the hydrogen atoms.

O

H

H

-

+

+The water molecule is a ………………………….- it has two oppositely charged “poles”.

+ -OH

OH

H+ -

H

This unequal sharing of electrons creates a polar molecule has two …………… charged areas in it.

Bond Polarity in Water

The oxygen atom has greater electronegativity so it attracts the electrons more strongly than the hydrogen atoms.

O

H

H

-

+

+The water molecule is a DIPOLE - it has two oppositely charged “poles”.

+ -OH

OH

H+ -

H

This unequal sharing of electrons creates a polar molecule has two oppositely charged areas in it.

OH

H

+

-

+

H Cl-+

HH

HN-

+

+

+ B

Cl

Cl

Cl

-

+

++

B

Cl

Cl

Cl

Ionic Bonding Formed when there is a

…………. of …………………...

Formed between ………….. and ………………….

Metals …………………….. and become ……………………... ions

- CATIONS.

Non metals …………………... and become …………………………. ions - ANIONS.

…………………………… between oppositely charged ions bonds the ions together.

Na.

..

:Cl: -

..

Na+

.:Cl: ..

..

Na. + : Cl: --> [Na]+ [Cl]-

.

ELECTROSTATIC ATTRACTION

There is a transfer of electrons.

Occurs when metals and non metals.bond

Metals lose electrons and become positively charged ions - CATIONS.

Non metals gain electrons and become negatively charged ions - ANIONS.

Electrostatic attraction between oppositely charged ions bonds the ions together.

Na.

..

:Cl: -

..

Na+

.:Cl: ..

..

Na. + : Cl: --> [Na]+ [Cl]-

.

ELECTROSTATIC ATTRACTION

Ionic Bonding

Sodium atom

Sodium ion• Smaller• positive

Chlorine atom

Chloride ion• Negative• bigger

Ionisation EnergyThe ENERGY REQUIRED to REMOVE AN ELECTRON completely from an atom in the GAS PHASE.

Sodium atom Sodium ion

Whenever ionic bonding occurs this process must take place.

Gas phase:The atoms are in the gas phase as the energy put in has melted and vapourised them.

ELECTRON AFFINITY

The amount of ENERGY RELEASED when an electron is added to a gaseous atom. This always accompanies the formation of an ionic bond.

e-

Bond Type vs Electronegativity

WCED Boundaries

ΔEneg 0 0<x<1 1 < x ≤ 2.1

2.1 < X

Bond Type

Pure Covalent

(Non Polar)

Covalent (weakly polar)

Polar-covalent Ionic

(In “General Chemistry” Linus Pauling writes: “The farther away two elements are from one another

on the scale, the greater is the amount of ionic character of a bond between them. When the separation on the scale is 1.9 the bond has about 50% ionic character.

If the separation is greater than this, it would seem appropriate to write an ionic structure for the substance, and if less, to write a covalent structure.

No rigid adherence to such a rule is called for however.)

Bonding - Metallic Bonding

- Exists between metal atoms.

- Metal electrons are weakly held - therefore they become delocalized (move from one atom to another).

- This leaves a lattice of positive ions - which become surrounded by a ‘sea’ of delocalized electrons.

- A force of electrostatic attraction exists between the delocalized electrons and the positive ions which is the metallic bond.

All the properties of metals can be explained in terms of this bonding.

Since the electrons are weakly held metals CONDUCT electricity.

Formation of Ionic BondA large amount of

energy (lattice) is released when the gaseous ions bond together into the ionic crystal lattice.

Ionic compounds are therefore very stable and require large amounts of energy to break the bonding.

Ionic compounds have HIGH MELTING POINTS we say they are thermally stable.

Na(s) + 1/2 Cl2(g) NaCl(s)

Na(g) + 1/2 Cl2(g)

Na(g) + Cl(g)

Na+(g) + ….+ Cl(g)

Na+(g) + Cl

-(g)

…………………Energy

……………….. Energy

…………………….Energy

Electron ………...

………Energy

Born-Haber Cycle

Formation of Ionic BondA large amount of

energy (lattice) is released when the gaseous ions bond together into the ionic crystal lattice.

Ionic compounds are therefore very stable and require large amounts of energy to break the bonding.

Ionic compounds have HIGH MELTING POINTS we say they are thermally stable.

Na(s) + 1/2 Cl2(g) NaCl(s)

Na(g) + 1/2 Cl2(g)

Na(g) + Cl(g)

Na+(g) + e- + Cl(g)

Na+(g) + Cl-

(g) Ionisation Energy

Dissociation Energy

Sublimation Energy

Electron Affinity

Lattice Energy

Born-Haber Cycle

Electrical conductivity

anion cation

No free moving charges in the solid state.

The ions are free to move if acted upon by an electric field.

Poslitive electrode

Negative electrode

IONIC SOLIDS DO NOT CONDUCT ELECTRICITY

BUT IONIC LIQUIDS & SOLUTIONS DO

IONIC SOLID IONIC LIQUID OR SOLUTION

Bonding SummaryCovalent Non metals Shared

electrons Molecules

Ionic• Metals + non metals • +/- Ions - Lattice• electrostatic attraction

Metallic• Metals• “delocalised”

electrons

H xH•

Cl-Na+

Properties• Non - conducting• (Electrons held in

bond.)• V Low or V High

melting points• Insoluble (H2O)

Properties• High Melting points• Soluble (H2O)• Conduct electricity when

ions free to move(liquid or solution).

Properties• Good Conductors• Malleable• Ductile• Luster (shiny).

H-H

Eg Hydrogen (H2)

Dissolution (dissolving) of an Ionic Solid Polar water molecules

Dipoles on the water molecules are attracted to the ions in the ionic solid

The ionic solid is broken apart by the water molecules

Bonding Summary Metallic – bonding between metals

Similar electronegativities (small) – delocalized electrons

Covalent - equal sharing of electrons Similar electronegativities (Large) ΔEneg < 0.4

Polar covalent - unequal sharing of electrons, dipoles Polar bonds - ΔEneg < 1.6 Polar molecules: Polar bonds & Asymmetrical shape

Ionic - complete transfer of electrons, ions formed, VERY different electronegativities.

Increasing electronegativity DIFFERENCE.

Atomic Radius

Atoms have linear dimensions. If one considers the atom as a sphere, we can define the radius of that atom as the smallest distance that this atom can approach another atom under a given bonding situation.

The atomic radius is determined by the effective volume of the outermost electronic level, and not by the size of the nucleus.

Values of atomic radii depend therefore on the binding state of the atom, and also on the method used to measure such radii.