Ionic and covalent bonding

Ionic and covalent bonding Ionic bonding Ionic Bonding Covalent 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 compounds Reinforce valency Explain 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 Chloride Iron + oxygen = Iron oxide Potassium + chlorine = Tin + sulphur =

Salts Anioniccompoundthatcontains a metal orammonium ion and a non metal orpolyatomic ion otherthan OH-.

Polyatomic ions Some groups of non metals or occasionally combinations of metals and nonmetals form polyatomic ions. These have names like: Carbonates Sulphates, Nitrates Ammonium Dichromate Again they follow the rule cations first, anions second E.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 highest Caesium 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 Covalent Na 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-N CuO

Polarity of more complex molecules E.g. Carbon dioxide O=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 dimensions By comparison water is polarised as both hydrogens are on one side Balanced complex molecules are unpolarised Unbalanced ones are polarised This relates to their 3D shape

Ionic and covalent bonding