C07 chemical bonding

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LEARNING OUTCOMES

Explain the formation of ionic bonds; Define and give examples of ionic solids; Explain the formation of covalent bonds; Define and give examples of simple

molecular solids; Explain metallic bonding; Relate the structure of sodium chloride to its

properties;

Chemical BondingChapter 7

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LEARNING OUTCOMES

Distinguish between ionic and simple molecular solids;

Explain the term allotropy; Define and give examples of giant molecular

solids; Relate the structure of diamond and graphite

to their properties


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The Electronic Structure of Noble Gases The noble gases like helium, neon and argon, which are in

Group 0 of the Periodic Table, are very unreactive. They do not form bonds with other atoms. They have fully filled outermost (valence) shells. Except for helium, which has 2 outer electrons, all the other

noble gases have 8 outer electrons.


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The Electronic Structure of Noble Gases The outer shell of 8 electrons is called an octet

structure and it makes the atom very stable. E.g. Helium, neon, argon

Atoms of other elements become stable like the noble gases by losing or gaining electrons or by sharing electrons.

They achieve this by forming bonds with other atoms.


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Types of Bonds

Covalent Bond Ionic Bond

Sharing of Electrons Transfer of Electrons

Between Non-metals Between Metal + Non-metal


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Ionic Bonds When sodium reacts with chlorine, the sodium atom loses

an electron to become a positively charged sodium ion:


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Ionic Bonds The chlorine atom gains an electron to become a

negatively charged chloride ion:


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Ionic Bonds The positive sodium ion and the negative chloride ion then

attract each other to form sodium chloride.

Sodium chloride is called an ionic compound.


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Other ionic compounds

Another example of an ionic compound is that formed between magnesium and chlorine.

Each magnesium atom transfers 2 electrons, one to each chlorine atom, to form magnesium chloride.

The formula of magnesium chloride is therefore given as MgCl2.


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Quick check 11. Ionic bonds are formed between a ______ and a _____.

2. A metal atom ______ an electron to form a _______ ion while a non-metal ______ an electron to become a ________ ion.

3. The two oppositely charged ions ________ each other to form an ______ compound.

4. An ionic bond is formed by the _________ of _______.

5. (a) Is aluminium oxide an ionic or covalent compound?(b) State the formula of aluminium oxide.

Solution


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1. Ionic bonds are formed between a metal and a non-metal.

2. A metal atom loses an electron to form a positive ion while a non-metal gains an electron to become a negative ion.

3. The two oppositely charged ions attract each other to form an ionic compound.

4. Ionic bond is formed by the transfer of electrons.

5. (a) Aluminium oxide is an ionic compound.(b) Al2O3

Return


Solution to Quick check 1

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Covalent Bonds

To achieve a more stable structure like helium, it needs one more electron in the first shell.

So two hydrogen atoms join together and share their electrons. A hydrogen molecule is formed.

A hydrogen atom has only one electron in its first shell.


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Covalent Bonds This sharing of electrons is called covalent bonding. In an oxygen atom, the outer shell has 6 electrons, so to achieve

an octet structure of 8 electrons like neon, two oxygen atoms combine to share 4 electrons.

This is called a double bond.


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Other covalent molecules

Water

H2O (2 single bonds)

Methane

CH4 (4 single bonds)


OOHH HHCC

HH

HHHH

HH

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Quick Check 2 1. The joining of atoms to form a molecule is called

__________ ________ .2. The two types of bonds are ________ bond and

________ bond.3. Covalent bonds are formed by the _________ of

_________ .4. Ionic bonds are formed by the __________ of_________ .5. _________ ______ are formed between non-metals

e.g. hydrogen, oxygen and carbon.Solution


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1. The joining of atoms to form a molecule is calledchemical bonding .

2. The two types of bonds are covalent bond and ionic bond.

3. Covalent bonds are formed by the sharing ofelectrons .

4. Ionic bonds are formed by the transfer ofelectrons .

5. Covalent bonds are formed between non- metals e.g. hydrogen, oxygen and carbon.

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Lesson 2

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Properties of Covalent Compounds The intermolecular forces

between the molecules are weak so covalent compounds have low melting and boiling points. For example, water, a covalent compound, has a melting point of 0 oC and a boiling point of 100 oC.

Weak intermolecular forces


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Properties of Covalent Compounds Covalent compounds do not

conduct electricity in any state.

Most covalent compounds are insoluble in water. Instead they are soluble in organic solvents.For e.g. iodine is insoluble in water, but soluble in ethanol. Pure water does not

conduct electricity

waterwater


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Properties of Ionic Compounds The electrostatic forces

between the oppositely-charged ions are very strong so ionic compounds have very high melting points and boiling points. For e.g. sodium chloride, an ionic compound, has a melting point of 801 oC and a boiling point of 1 517oC.


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Properties of Ionic Compounds Ionic compounds conduct

electricity when molten or dissolved in water. This is because the ions can move about and conduct electricity.

Molten sodium chloride conducts electricity.

Most ionic compounds are soluble in water, but insoluble in organic solvents.

For e.g. sodium chloride is soluble in water, but insoluble in oil or petrol.


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Summary

Ionic Compounds Covalent Compounds

Have very high melting and boiling points

Have low melting and boiling points

Conduct electricity when molten or in aqueous solution

Cannot conduct electricity in any state

Are usually soluble in water, but insoluble in organic solvents

Are usually insoluble in water, but soluble in organic solvents

Differences between Ionic and Covalent Compounds


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Quick check 31. Covalent compounds have _______ forces of attraction

between the molecules, so they have ____ melting points and ______ boiling points.

2. Ionic compounds have very ______ forces of attraction between the oppositely charged ions, so they have very ______ melting points and ______ boiling points.

3. All covalent compounds cannot _____ _______ .4. All ionic compounds can conduct ________ when they are

_______ or ________ in water.5. Sugar is a covalent compound but it is soluble in water. State

one test you would use to show that sugar is a covalent compound.

Contd.


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Quick check 3 (cont.)6. The table below shows 3 substances.

(a) Which substance is an ionic compound?(b) Which substance is a metal?(c) Which substance could be a covalent compound? Solution


Substance Electrical Conductivity

when solid when molten

A does not conduct does not conduct

B does not conduct conducts

C conducts conducts

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1. http://www.quia.com/jq/19617.html

2. http://www.purchon.com/chemistry/bonding.htm

To learn more about Chemical Bonding, click on the links below!


http://www.quia.com/jq/19617.html

http://www.purchon.com/chemistry/bonding.htm

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1. Covalent compounds have weak forces of attraction between the molecules, so they have low melting points and low boiling points.

2. Ionic compounds have very strong forces of attraction between the oppositely charged ions, so they have very high melting points and high boiling points.

3. All covalent compounds cannot conduct electricity.4. All ionic compounds can conduct electricity when they are molten

or dissolved in water.5. Dissolve some sugar in water, then try to pass electricity through

it. The sugar solution will not able to conduct electricity. Contd.



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Substance Electrical Conductivity

when solid when molten

A does not conduct does not conduct

B does not conduct conducts

C conducts conducts

6. The table below shows 3 substances.

(a) Ionic compound: B(b) Metal: C(c) Covalent compound: A

Return


Solution to Quick check 3 (contd.)

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Simple moleculesSimple molecules Many covalent substances like water, Many covalent substances like water,

methane, carbon dioxide and iodine methane, carbon dioxide and iodine exist as small molecules. exist as small molecules.

These compounds are said to have These compounds are said to have simple molecular structuressimple molecular structures. .

Macromolecular StructuresChapter 7

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MacromoleculesMacromolecules Some covalent substances like silicon Some covalent substances like silicon

dioxide (SiOdioxide (SiO22), diamond and graphite are ), diamond and graphite are made up of very large molecules.made up of very large molecules.

These substances are said to have These substances are said to have macromolecular structuresmacromolecular structures. .


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Properties of MacromoleculesProperties of Macromolecules Due to the large structures of these macromolecules, Due to the large structures of these macromolecules,

their chemical and physical properties are different their chemical and physical properties are different from those of the simple molecules.from those of the simple molecules.

The macromolecules are solids with very high melting The macromolecules are solids with very high melting and boiling points.and boiling points.E.g. The melting point of diamond is 3550 E.g. The melting point of diamond is 3550 ooC, C, compared to 0 compared to 0 ooC for water. C for water.

Due to their sizes, they are also not as reactive Due to their sizes, they are also not as reactive compared to the simple molecules. compared to the simple molecules.


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Metallic bondingMetallic bonding Metals are also made up of very large lattice structures.Metals are also made up of very large lattice structures. The metallic structure consists of a lattice of positive ions The metallic structure consists of a lattice of positive ions

in a “sea of electrons”. in a “sea of electrons”. Metals are malleable because the layers of atoms can Metals are malleable because the layers of atoms can

slide over one another easily as they are being arranged slide over one another easily as they are being arranged in neat layers.in neat layers.


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Properties of Metallic structureProperties of Metallic structure The closely packed positively charged metallic ions The closely packed positively charged metallic ions

form a lattice structure with the outer electrons form a lattice structure with the outer electrons moving freely around the whole metallic structure.moving freely around the whole metallic structure.

The electrostatic attraction between the metallic The electrostatic attraction between the metallic ions and the electrons holds the metallic ions tightly ions and the electrons holds the metallic ions tightly in the lattice and this gives the metal a in the lattice and this gives the metal a high high melting point.melting point.

The free electrons are able to move and The free electrons are able to move and conduct electricity and heat.conduct electricity and heat.

This explains why metals are good This explains why metals are good conductors of heat and electricity.conductors of heat and electricity.


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Van der Waals Forces-Van der Waals forces of attraction can exist between atoms and molecules.

-They are not the same as ionic or covalent bonds. They arise because of fluctuating polarities of nearby particles.

-The shape and size of molecules affect the strength of the van der Waals forces. The larger the force, the higher the melting and boiling point.

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Structure of diamondStructure of diamond

In diamond, In diamond, each carbon atom is linked to four other each carbon atom is linked to four other carbon atomscarbon atoms by strong covalent bonds. by strong covalent bonds.

The carbon atoms are arranged in a The carbon atoms are arranged in a tetrahedral tetrahedral structurestructure which extends throughout the whole diamond which extends throughout the whole diamond lattice made up of millions of atoms.lattice made up of millions of atoms.

The diamond structure is very rigid and the bonds are The diamond structure is very rigid and the bonds are very strong and difficult to break. This explains why very strong and difficult to break. This explains why diamond is diamond is very hardvery hard and and strongstrong and has a and has a very high very high melting pointmelting point (3550 ºC) and (3550 ºC) and very high boiling pointvery high boiling point (4827 ºC).(4827 ºC).


Structure of diamond

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Structure of graphiteStructure of graphite

In graphite,In graphite, each carbon atom is linked to three other each carbon atom is linked to three other carbon atomscarbon atoms in the same plane by strong covalent in the same plane by strong covalent bondsbonds. . The carbon atoms form six-member hexagonal rings that link up

to form flat layers. The hexagonal rings are arranged in parallel layers with weak forces of attraction between the atoms in each layer.


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Properties of graphiteProperties of graphite The covalent bonds between the atoms in The covalent bonds between the atoms in

each layer are strong, and a lot of heat energy each layer are strong, and a lot of heat energy is required to break these bonds when graphite is required to break these bonds when graphite melts. This explains why graphite has a very melts. This explains why graphite has a very high melting point (3652 high melting point (3652 ooC ). C ).

Not all the electrons in graphite are used in bonding. There are some free electrons which enable graphite to conduct electricity.

strong covalent bonds

weak forces

The forces of attraction between the atoms in each layer is weak. The layers can easily slide away from each other when a force is applied. For this reason, graphite is smooth and slippery.


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Summary of properties Summary of properties


PropertyProperty DiamondDiamond GraphiteGraphite

Hardness and Hardness and TextureTexture

Very hard and strongVery hard and strong Soft, smooth and Soft, smooth and slipperyslippery

Melting point and Melting point and Boiling pointBoiling point

Very highVery high Very highVery high

Electrical Electrical ConductivityConductivity

Does not conduct Does not conduct electricityelectricity

Conducts electricityConducts electricity

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Uses of diamondUses of diamond Due to their differences in properties, diamond and Due to their differences in properties, diamond and

graphite are used in different ways. graphite are used in different ways. Diamond being hard and strong, is used for making Diamond being hard and strong, is used for making

cutting and drilling toolscutting and drilling tools. . Another use for diamond is for making jewelleryjewellery.


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Uses of graphiteUses of graphite Graphite being smooth and slippery, is used in making Graphite being smooth and slippery, is used in making

lubricantslubricants for use in machinery, motorcar engines and for use in machinery, motorcar engines and even bicycle chains. even bicycle chains.

Due to its very high melting point, graphite is used as a heat insulatorheat insulator. It is used to coat the nose of a space shuttle.

Graphite being chemically unreactive and a conductor Graphite being chemically unreactive and a conductor of electricity, is used in making of electricity, is used in making electrodeselectrodes for use in for use in electrolysis and in dry cells. electrolysis and in dry cells.


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Quick check 4Quick check 4 1.The table below shows the properties of 4 substances.

Element Conducts electricity in Melting point(OC)Solid state Liquid state

W good good 1085

X poor good 801

Y poor poor 3550

Z poor poor 114

Deduce the type of bonds that each substance has.

Solution


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Quick check 4 (cont’d)Quick check 4 (cont’d) 2.The pictures below show 4 types of molecular structures.

Identify the substance or the type of bonds shown by each structure.

A B

C D

Solution


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Solution to Quick check 4Solution to Quick check 4

1. W: metallic bonding, X: ionic bonding, Y: macromolecular (diamond), Z: simple molecular

B: silicon dioxide; macromolecular

D: ionic crystal latticeC: metallic bonding

2. A: graphite; macromolecular

Return


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• http://mineral.galleries.com/minerals/elements/graphite/graphite.htm

• http://www.chemguide.co.uk/atoms/bonding/metallic.html

To learn more about Macromolecular Structures, click on the links below!


ReferencesReferences Chemistry for CSEC Examinations by

Mike Taylor and Tania Chung

Longman Chemistry for CSEC by Jim Clark and Ray Oliver

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C07 chemical bonding

Science

Transcript of C07 chemical bonding