CHEMICAL BONDING Part 1 Introduction to Chemical Bond Formation
Doc Brown's Science–Chemistry Chemical Bonding GCSE/IGCSE/AS/A2 O Level Revision Notes
The five linked pages introduce to the concept of a chemical bond and why atoms bond together, types of chemical bonds and which electron arrangements are particularly stable leading to stable chemical bonds. Through the use of dot and cross electronic diagrams is described and there are detailed notes on ionic bonding i.e. the mutual attraction of oppositely charged ions to give ionic bonds and the properties of ionic compounds, covalent bonds and the formation of small simple molecules and their properties, macromolecules like polymers and giant covalent structures like diamond, graphite and silica. Finally metallic bonding is described to explain the structure and physical properties of metals. These notes on chemical bonding are designed to meet the highest standards of knowledge and understanding required for students/pupils doing GCSE chemistry, IGCSE chemistry, O Level chemistry, KS4 science courses and a basic primer for AS/A Level chemistry courses.
Part 1 Introduction – why do atoms bond together? (this page, read first)
and sub–index for Parts 2–5 (this page)
(Part 6 More advanced concepts for advanced level chemistry)
(in preparation, BUT a lot on intermolecular forces in Equilibria Part 8)
Keywords/phrases/names sub–index for Parts 2–5: Examples of ionic compounds described: sodium chloride NaCl (exemplar for any Li/Na/K + F/Cl/Br/I combination), magnesium chloride MgCl2 (exemplar for any Mg/Ca + F/Cl/Br combination), aluminium fluoride AlF3, potassium oxide K2O (exemplar for any Li/Na/K + O/S combination), magnesium/calcium oxide MgO/CaO and magnesium/calcium sulphide (MgS/CaS), aluminium oxide Al2O3 (exemplar for Al2S3) * Examples of covalent molecules: simple small molecule bonding e.g. water * physical properties of small molecules * giant network bonding – giant molecules e.g. carbon C–diamond/graphite, silicon Si/silica SiO2 * properties of giant covalent structures * polymers/plastics * properties of polymers * inter/intra (internal)–molecular forces * hydrogen H2, chlorine Cl2, hydrogen chloride HCl, water H2O, ammonia NH3, methane CH4, oxygen O2, carbon dioxide CO2, ethene C2H4, nitrogen N2, ethane C2H6, chloromethane CH3Cl, methanol CH3OH, carbon (diamond), carbon (graphite), carbon (buckminsterfullerene/fullerenes), silica/silicon dioxide SiO2 * examples of ionic compounds * physical properties of ionic compounds * If your ionic compound is not listed, look for a compound with a similar formula and you should be able to work it out from the example given. The use of the word exemplar implies you are dealing with the same set of outer electron arrangements (configurations), which is why you can work out lots more dot and cross diagrams of ionic compounds by understanding one example * metal bonding model element/alloys * physical properties of metals *
There are lots of dot and cross diagrams i.e. Lewis diagrams of bonding situations
(atomic number) electron arrangement
(a) IONIC BONDING – an ionic bond is formed by one atom transferring electrons to another atom to form oppositely charged particles called ions which attract each other – the ionic bond.
If a particle, as in a neutral atom, has equal numbers of protons (+) and electrons (–) the overall particle charge is zero
The proton/atomic number in an atom does not change BUT the number of associated electrons can!
If negative electrons are lost
If negative electrons are gained
The charge on the ion is numerically related to the number of electrons transferred i.e. electrons lost or gained.
For any atom or group of atoms, for every electron gained you get a one unit increase in negative charge on the ion, for every electron lost you get a one unit increase in the positive charge on the ion.
The atom losing electrons forms a positive ion (cation) and is usually a metallic element.
The atom gaining electrons forms a negative ion (anion) and is usually a non–metallic element.
The ionic bond then consists of the attractive force between the positive and negative ions in the structure.
The ionic bonding forces act in all directions around a particular ion, it is not directional, as in the case of covalent bonding.
The sodium (metal) atom transfers an electron to the chlorine (non–metal) atom in forming the ionic compound sodium chloride
The bonds between the ions is very strong and they club together to form a giant ionic lattice with a very high melting point because it takes a lot of energy to overcome the attractive forces between the ions - the ionic bonds.
When molten, or dissolved in water, ionic compounds will conduct electricity because the charged particles (ions) are free to move and carry the electric current.
For more detailed notes on this example and lots of other examples ...
(b) COVALENT BONDING – a covalent bond is formed by two atoms sharing electrons so that the atoms combine to form molecules.
(c) METALLIC BONDING isn't quite like ionic or covalent bonding, although the metal atoms form positive ions, no negative ion is formed from the same metal atoms, but the immobile positive metal ions/atoms in the lattice are attracted together by the free moving negative electrons between them. So, like ionic bonding, you do get attraction between positive and negative particles and this is the metallic bond.
(d) INTERMOLECULAR FORCES – INTERMOLECULAR BONDING
For more details see Covalent Bonding – small simple molecules and properties
(e) WHY DO SOME ATOM DO NOT READILY FORM CHEMICAL BONDS?
(f) Can we deduce the likely chemical bonding in a material from its physical and chemical properties?
New bonds formed! Poetry in motion!
Lots of energy released when metals like magnesium bond with oxygen!
Ionic Bonding Poem – a snippet of chemical poetry
(anon Y11 student, Whitby Community College, Oct 31st 2002)
How do I long for a full outer shell!
being chlorine having seven, is a horrid hell
but my name is sodium and I have one spare!
I want to lose it, can we not share?
No? for are we not a perfect match
chuck it to me, I promise to catch
then we can live our separate ways
and live with full shells to the end of our days!
and so our tale comes to an end
as positive and negative we shall remain friends
Its a good idea to have some idea of where the elements are in the periodic table, and their electronic structure, before looking at the theoretical electronic models for ionic, covalent or metallic bonding
Granddaughter Baby Niamh at nearly 6 months – first experiment in molecular modelling?
No teething dribbling on the structure please! The greatest chemistry of all – the chemistry of life!
Answers to the 'type of bonding' question
A is an ionic structure and bonding, giant ionic lattice, high melting/boiling point, only conducts when molten, the solubility and electrical conduction in water is extra evidence, but isn't definitive for substance A (see E).
B is a giant metallic lattice structure and metal bonds, high melting/boiling points, high density, conducts in solid, not just liquid.
C simple molecular structure, small molecules with covalent bonds, low melting/boiling point, no electrical conduction at all (no ions).
D giant covalent lattice, very high melting/boiling, no electrical conduction, won't dissolve in anything.
I've made A to D quite straightforward (as long as Bonding Parts 2 to 5 have been studied), but I've
E simple molecular structure, small molecules with covalent bonds, low melting/boiling point, no electrical conduction when molten, however it does conduct when dissolved in water, so ions must be formed to conduct electricity. The latter is a 'red herring', if it had an ionic structure the melting/boiling points would be much higher and the liquid would have conducted.
F Probably a thermally very stable giant covalent structure, but with weakly electrical conducting properties (even in the solid) due to delocalised electrons, completely insoluble. Its unlikely to be an ionic structure because it conducts in the solid. Metals do not decompose on heating to a high temperature and all metals will boil.
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