Bonding

K Warne

ClH X

+ -

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Covalent Molecules CH4, H2O, NH3,

CO2, NH4+,

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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

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Lewis acid & base

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

H3NBF3 Cu(NH3)4+

Cu(H2O)62+

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Electronegativity in a GroupElectronegativity in a Group

H

Li

Na

Group 1ElectronegativityElectronegativity

DECREASES

from TOP to BOTTOM in a

group

as the number of shells increase

bonding electrons bonding electrons (outer) are (outer) are further further

from nucleus from nucleus

and therefore and therefore LESS strongly LESS strongly

attracted.attracted.

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Electronegativity TrendsElectronegativity Trends

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

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

Group 1 2 3 4 5 6 7 8

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

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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

+

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Bond Polarity in Water

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

O

H

H

-

+

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

+ -OH

OOHH

HH++ --

H

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

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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 EnergySublimation Energy

Electron Affinity

Lattice Energy

Born-Haber Cycle

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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)

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Bonding Summary Metallic – bonding between metals

Similar electronegativities (small) – delocalized electrons

Covalent - equal sharing of electrons Similar electronegativities (Large) ΔEneg = 0

Polar covalent - unequal sharing of electrons, dipoles Polar bonds - ΔEneg < 1.9 Polar molecules: Polar bonds & Asymmetrical shape

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

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Keith Warne

Hi This is a SAMPLE presentation only.

My full presentations contain loads more slides (20-100) and are freely available on my Science Café Science Café website.

http://www.sciencecafe.org.za

(paste into your browser if link above does not work)

I have other resources available from my Science Café Science Café site feel free to have a look.

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