ELEMENTS AND BONDING

HTTP://WWW.YOUTUBE.COM/WATCH?V=CL6I1O1YHH0

Yr 10 Science

Atoms are rarely found by themselves, but instead join with other atoms.

 WHY DO ELEMENTS BOND?

This question is best answered by examining the Noble gases.

This “group” of atoms are inert (non-reactive). In fact, Helium, Neon and Argon never react with other atoms, or even themselves. This is because they have either 8 electrons in their outer shells, or a full outer shell.

Noble gases have a very “stable” electron configuration.

Other atoms will react with other atoms so they can achieve a similar electron configuration by either:

• gaining or losing outer shell electrons (Ionic Bonding), or

• sharing electrons (Covalent Bonding).

Compounds are formed when different atoms react or join together. There are three main ways in which these atoms may join together:

1. Ionic bonding2. Covalent bonding3. Metallic bonding

IONIC BONDING

This occurs when a metal atom joins to a non-metal atom and electrons are transferred from the metal to the non- metal atom. e.g. NaCl

Na+ + Cl- NaCl(2, 8) (2, 8, 8)

Lets look closely at NaCl

e.g. MgO

Mg2+ + 2Cl- MgCl2

(2, 8) (2, 8, 8)

IONIC BONDING

Metal atoms lose their outer shell electrons to non-metal atoms. The metal atoms then become positive ions (cations).

Non-metal atoms gain outer shell electrons from metal atoms to become negative ions (anions).

The charge on an ion is called its valency.

The ratio of metal atoms to non-metal atoms in an ionic compound is determined by each ions valency.

**Handout valency sheet***Naming Ionic Compound Activity

Oppositely charged ions (positive cations & negative anions) are attracted to each other through electrostatic attraction.

Bond Master Activity

Activities – Writing Formula for Ionic Compounds

Complete the following table

CationAnion

X+ X2+ X3+

Y-

Y2-

Y3-

CationAnion

X+ X2+ X3+

Y- XY XY2 XY3

Y2- X2Y XY X2Y3

Y3- X3Y X3Y2 XY

anion

cation SodiumNa+

AluminiumAl3+

CalciumCa2+

MagnesiumMg2+

LithiumLi2+

ChlorideCl-

         

OxideO2-

         

FluorideF-

         

SulphideS2-

         

NitrateNO3

-

         

SulfateSO4

2-

         

PhosphatePO4

3-

         

Hydrogen carbonateHCO3

-

         

Sodium chlorideNaCl

cation

anion

SodiumNa+

AluminiumAl3+

CalciumCa2+

MagnesiumMg2+

LithiumLi+

ChlorideCl-

Sodium chloride

NaCl

Aluminium chloride

AlCl3Calcium chloride

CaCl2Magnesium chloride

MgCl2Lithium chloride

LiCl

OxideO2-

Sodium oxide

Na2OAluminium oxide

Al2O3

Calcium oxide

CaOMagnesium oxide

MgOLithium oxide

Li2O

FluorideF-

Sodium fluoride

NaF

Aluminium fluoride

AlF3

Calcium fluoride

CaF2

Magnesium fluoride

MgF2

Lithium fluoride

LiF

SulfideS2-

Sodium sulpfide

Na2S

Aluminium sulfide

Al2S3

Calcium sulfide

CaSMagnesium sulfide

MgSLithium sulfide

Li2S

NitrateNO3

-

Sodium nitrate

NaNO3

Aluminium nitrate

Al(NO3)3

Calcium nitrate

Ca(NO3)2

Magnesium nitrate

Mg NO3)2

Lithium nitrate

Li NO3

 

cation

anion

SodiumNa+

AluminiumAl3+

CalciumCa2+

MagnesiumMg2+

LithiumLi+

SulfateSO4

2-

Sodium sulfate

Na2SO4

Aluminium sulfate

Al2 (SO4)3

Calcium sulfate

CaSO4

Magnesium sulfate

MgSO4

Lithium sulfate

Li2SO4

PhosphatePO4

3-

Sodium phosphate

Na3PO4

Aluminium phosphate

AlPO4

Calcium phosphate

Ca 3(PO4)2

Magnesium phosphate

Mg3(PO4)2

Lithium phosphate

Li3(PO4)

Hydrogen carbonateHCO3

-

Sodium Hydrogen carbonate

NaHCO3

Aluminium Hydrogen carbonate 

Al(HCO3)3

Calcium Hydrogen carbonate 

Ca(HCO3)2

Magnesium Hydrogen carbonate 

Mg(HCO3)2

Lithium Hydrogen carbonate

LiHCO3

COVALENT BONDING

This occurs when two or more non-metal atoms join together by sharing electrons.

e.g. H2O and CO2.

Why do they share electrons?

e.g. Consider a H2 molecule.Both H atoms need to gain electrons in order to achieve a complete outershell. They achieve this complete outershell by sharing pairs of electrons and this is called a covalent bond.

A covalent bond is the electrostatic attraction between the negatively charged shared pair of electrons and the positive nucleus of each atom.

The electrostatic attraction holds the atoms together and forms the molecule.

Metallic Bonding

Metallic bonding is the bond formed by positive ions surrounded by a sea of valence electrons.

Positive ions (CATIONS) – in fixed positions

Delocalised Electrons –freely moving around the cations

LATTICE

The electrostatic forces of attraction between the positively charged cations and negatively charged electrons hold the lattice together.

Animation of Metallic Bondinghttp://www.drkstreet.com/resources/metallicbonding-animation.swf