Covalent bonding

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Covalent bondingCovalent bonding

1.demonstrate an understanding that covalent bonding is strong and arises from the

electrostatic attraction between the nucleus and the electrons which are between the nuclei,

based on the evidence:

i the physical properties of giant atomic structures

ii electron density maps for simple molecules

Covalent bondingCovalent bonding

2.draw electron configuration diagrams for simple covalently bonded molecules, including those with multiple bonds and dative covalent

bonds, using dots or crosses to represent electrons.

Chemical Bonds A compound is a substance where two, or more atoms of elements are joined together by a chemical bond.

A chemical bond involves either the transfer or the sharing of the electrons in the highest occupied energy levels of an atom.

Covalent Bonds where electrons are shared.

Ionic Bonds where electrons are transferred completely

There are two types of chemical bonds:

There are two types of covalent substances, i.e. Simple Covalent Molecules and Giant Covalent Structures.

Simple covalent compounds usually have a low melting point, and are therefore soft solids, liquids or gases.

Particles of simple covalent compounds are known as molecules.

Sugars are typical examples... Sucrose(m.p. 185 ºC)

Glucose(ball and stick model)

Fructose(found in fruit)

Simple Covalent Molecules

The gaseous elements hydrogen, oxygen, nitrogen and chlorine are also simple covalent, diatomic molecules.

Giant covalent substances have strong bonds and associated high melting and boiling points. They are also insoluble in water.

Diamond and graphite are typical examples...Diamond

(m.p. 3,547 ºC)

Graphite

Giant Covalent Structures Giant Covalent Structures

Silica is a compound ofsilicon and oxygen and isbetter known as sand.Silica has a giant covalent structureand a melting point of 1,723 ºC.Sand is insoluble in water, relatively hard, and is widely used as an abrasive or to make glass.

Giant Covalent Structures

This diagram shows the electronic configuration of hydrogen, and the non-metallic elements in the first short period of the Periodic Table.

How Covalent Bonds Form

In order to gain a full outer shell of electrons, atoms of some elements can share electrons with other atoms. This makes the atoms more stable.

How Covalent Bonds Form

The process of sharing electrons is known as covalent bonding.

Hydrogen atoms each need one electron;

Carbon atoms each need four electrons;

Nitrogen atoms each need three electrons;

Oxygen atoms each need two electrons;

Fluorine atoms each need one electron;

Neon atoms already have a full outer electron shell.

In order to achieve a full outer shell...

How Covalent Bonds Form

Atoms of certain elements can covalently bond with other atoms of the same or different elements.

The only atom shown which has a full outer shell of electrons, is that of neon. This is why neon, and the other inert gases, do not readily form compounds.

2,8,18,18,7

F9

Cl17

Br35

I53

2,7

2,8,7

2,8,18,7

As a result of this, they form compounds with similar formulas

Elements which are in the same group of the Periodic Table, have the same number of electrons in their outer electron level.

Electronic Structure and Compounds Electronic Structure and Compounds

F2

Cl2

Br2

I2

HF

HCl

HBr

HI

Chlorine Molecule (Cl2)

Chlorine atoms form simple molecules (diatomic) by sharing single electrons.

Chlorine Molecule (Cl2)

Chlorine atoms form simple molecules (diatomic) by sharing single electrons.

Chlorine Molecule (Cl2)

The sharing of one pair of electrons constitutes a single covalent bond.

Each chlorine atom has one space in its outer shell, and can share this with another atom, which also donates one electron to the bond.

Chlorine Molecule (Cl2)

The diagram shows the chlorine atoms sharing two electrons in total, forming a single covalent bond.As a result of this sharing, both atoms effectively have a full outer shell of electrons.

A chlorine molecule, Cl2 is the result.

The Methane Molecule (CH4)

One carbon atom shares four electrons with the hydrogen atoms.

Each hydrogen atom shares one electron with the carbon atom.

The sharing of a pair of electrons constitutes a single covalent bond.

Therefore, four covalent bonds are formed.

Both carbon and hydrogen atoms have an incomplete outer shell.

N.B. Hydrogen is drawn larger for clarity on this and subsequent slides.

The Methane Molecule (CH4)

As a result of this sharing of electrons, each of the five atoms effectively has a full outer shell of electrons.

A methane molecule, CH4 is the result.

The Methane Molecule (CH4)

The Methane Molecule (CH4)Start the animation to see how the four covalent bonds form...

CH

HH H

Multiple Covalent BondsMultiple Covalent Bonds

In all the examples shown so far, the covalent bonds formed are single bonds, formed when one pair of electrons is shared between two atoms.

The following examples show how double and triple covalent bonds can be formed between atoms.

There are no known examples of quadruple covalent bonds.

The Oxygen Molecule, O2

Double Bonds in an Oxygen MoleculeOxygen atoms form simple molecules (diatomic) by sharing single electrons.

Double Bonds in an Oxygen MoleculeOxygen atoms form simple molecules (diatomic) by sharing single electrons.

The sharing of two pairs of electrons constitutes a double covalent bond.

Each oxygen atom has two spaces in its outer shell, and can share these with the other oxygen atom, which also donates two electrons to the bond.

The diagram shows the oxygen atoms sharing four electrons in total, forming a double covalent bond.As a result of this sharing, both atoms effectively have a full outer shell of electrons.

An oxygen molecule, O2 is the result.

Double Bonds in an Oxygen Molecule

The Nitrogen Molecule, N2

Triple Bonds in a Nitrogen MoleculeNitrogen atoms form simple molecules (diatomic) by sharing single electrons.

Triple Bonds in a Nitrogen MoleculeNitrogen atoms form simple molecules (diatomic) by sharing single electrons.

The sharing of three pairs of electrons constitutes a triple covalent bond.

Each nitrogen atom has three spaces in its outer shell, and can share these with the other nitrogen atom, which also donates three electrons to the bond.

The diagram shows that the nitrogen atoms can share six electrons in total, forming a triple covalent bond.

As a result of this sharing, both atoms effectively have a fullouter shell of electrons.

A nitrogen molecule, N2 is the result.

This bond is one of the strongest covalent bonds in nature.

Triple Bonds in a Nitrogen Molecule

Electron density of a hydrogen atom

Electron density of a fluorine molecule

Electron density of a hydrogen molecule

Electron density of a hydrogen fluoride molecule