Ionic and covalent bonding

Covalent bonding

Ionic bondi

ngIonic Bonding

Bonding as you’ve never imagined it

http://www.youtube.com/watch?v=BCYrNU-7SfA

Objectives

To consider the features of ionic and covalent bonds, and the compounds they make.

Naming of ionic and covalent compoundsReinforce valencyExplain how electronegativity affects bond

type

Outcomes

By the end you must be able to describe the differences of the two types of bonds and relate these to the different properties of ionic and covalent bond compounds.

You must understand the influence of electronegativity and be able to relate this to the properties of compounds.

Ionic and covalent bonding

http://www.youtube.com/watch?v=QqjcCvzWwww

More on covalency if you want

http://videos.howstuffworks.com/hsw/8394-physical-science-series-covalent-bonds-video.htm

http://www.youtube.com/watch?v=oNBzyM6TcK8

Time to research

What are the differences between ionic and covalent bonds and what different properties do their compounds have?

Take notes from handout!

Naming ions

Positive ions are formed by atoms of metals that give away electrons

These are called cations and are always written first in compounds.

Negative ions are formed by atoms of non metals that receive electrons.

These are called anions and are written second.

Naming ionic compounds (Binary salts)

Made from a metal and a non metal (or non metals)

Metal keeps its name, non metal changes slightly

Sodium + Chlorine = Sodium ChlorideIron + oxygen = Iron oxidePotassium + chlorine =Tin + sulphur =

Salts

An ionic compound that contains a metal or ammonium ion and a non metal or polyatomic ion other than OH-.

Polyatomic ions

Some groups of non metals or occasionally combinations of metals and nonmetals form polyatomic ions. These have names like:

CarbonatesSulphates, Nitrates AmmoniumDichromateAgain they follow the rule cations first, anions

secondE.g. copper sulphate, ammonium nitrate etc.

Valencies of ions

The valency is………

Group 1E.g. Sodium = Na+

Group 2Magnesium = Mg2+

Group 3 Aluminium = Al3+

Group 7 Chloride = Cl-

Group 6 Oxide = O2-

Group 5 Nitride = N3- Group 4 Carbide = C4-

Transition metals

These too form positive ions, but may have more than one valency

E.g. iron can be Fe2+ or Fe3+

Written in compounds as Iron (ii) sulphate or Iron (iii) sulphate

Cobalt, manganese and chromium can also have 2+ and 3+ ions

Copper can be copper (i) and copper (ii)These variable valencies result from electrons

moving between supplemental electron shells d and f

Poly atomic ions

Some positive e.g. ammonium (NH4)+

Most negative because they are composed of non metals e.g.

Carbonate (CO3)2-

Sulphate (SO4)2-

Nitrate (NO3)-

Covalency

Remind me what does this mean?

Covalent molecules and compounds are made of nonmetals and can often have more than one compound made from the same two elements.

The extreme version of this is carbon. Millions of chemicals are made from simply carbon, hydrogen and oxygen

Common covalent compounds

Carbon dioxide (CO2)Carbon Monoxide (CO)Sulphur dioxide (SO2)Sulphur trioxide (SO3)Nitrogen monoxide (NO)Di nitrogen oxide (N2O)

Try and name these.

N2O3

N2O4

CS2

SiO2

SO3

SO2

SF6

ClO2

H2S

Polarity

Many molecules are polarised, i.e. one end has an opposite charge to the other.

It is the result of the relative electro negativity of the atoms in the molecule.

Electronegativity

All atoms have an electronegativity value.It is a measure of how easily the atom

attracts electrons to itself;As nonmetals accept electrons they must

have higher electronegativity values than metals

Fluorine has the highestCaesium and Francium have the lowest. High and low electronegativity imply

reactivity

Although this diagram is really helpful visually- its values do not agree with other tables so don’t use them!

Electronegativity continued

Small atoms tend to have higher electronegativity than larger ones,

Electronegativity increases up groups and from left to right in periods.

Transition metals tend to be low because electrons can move within the atom to fill the valence shell.

Nobel gases do not have electronegativity values as they do not make bonds (normally)!

Polarity of bonds

If there is a large difference in electronegativity values you will get ionic bonds and highly polarised particles;

Moderate difference results in covalent bonds which form polarised covalent compounds, e.g. water or Hydrogen chloride.

Little or no difference means that the bonds are covalent and the molecules uncharged, e.g. when two of the same atoms are joined covalently as in the biatomic molecules of gases e.g. H2 and N2

Numbers

Differences in electronegativity 0 – 0.4 = non polar covalent

Differences of 0.5 – 1.8 will tend to lead to polar covalent bonds. (The greater the difference, the greater the polarity)

Differences greater than 1.8 will be ionic.

Work these out

E.g. H-H (H is 2.1) 2.1 – 2.1 = 0 CovalentNa Cl (Na is 0.9, Cl is 3.0) 3.0 – 0.9 = 2.1

(ionic)HCl (H is 2.1, Cl is 3) MgO (Mg is 1.3 O is 3.5)Nitrogen monoxide (N is 3 O is 3.5)Hydrogen Bromide (H is 2.1 Br is 2.8)Carbon Monoxide (C is 2.5 O is 3.5)N-NCuO

Polarity of more complex molecules

E.g. Carbon dioxideO=C=O The two bonds cancel each other out

so it is not polar (unlike Carbon monoxide)Also like this is CCl4 and CH4 as these are both

symmetrical in 3 dimensionsBy comparison water is polarised as both

hydrogens are on one sideBalanced complex molecules are unpolarisedUnbalanced ones are polarisedThis relates to their 3D shape