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Doc Brown's Chemistry - Chemical Bonding - Revision Notes Part 1 Introduction to the Chemical Bonding Revision KS4 Science IGCSE/O level/GCSE Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel 360Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science (revise courses equal to US grades 9-10) Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA OCR Edexcel Salters CIE revising courses for pre-university students (equal to US grade 11 and grade 12 and Honours/honors level courses) Part 1 Introduction - why do atoms bond together? (this page, read first) and sub-index for Parts 2-5 (this page) Part 2 Ionic Bonding - compounds and properties Part 3 Covalent Bonding -small simple molecules and properties Part 4 Covalent Bonding - macromolecules and giant covalent structures Part 5 Metallic Bonding - structure and properties of metals 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 *
Some atoms are very reluctant to combine with other atoms and exist in the air around us as single atoms. These are the Noble Gases and have very stable electron arrangements e.g. 2, 2,8 and 2,8,8 because their outer shells are full. The first three are shown in the diagrams below and explains why Noble Gases are so reluctant to form compounds with other elements.
All other atoms therefore, bond together to become electronically more stable, that is to become like Noble Gases in electron arrangement. Bonding produces new substances and usually involves only the 'outer shell' or 'valency' electrons and atoms can bond in two ways. The phrase CHEMICAL BOND refers to the strong electrical force of attraction between the atoms or ions in the structure. The combining power of an atom is sometimes referred to as its valency and its value is linked to the number of outer electrons of the original uncombined atom (see examples later). (a) IONIC BONDING - 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 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 metal. The ionic bonding forces act in all directions around a particular ion, it is not directional, as in the case of covalent bonding. (b) COVALENT BONDING - sharing electrons to form molecules with covalent bonds, the bond is usually formed between two non-metallic elements in a molecule. The two positive nuclei (due to the positive protons in them) of both atoms are mutually attracted to the shared negative electrons between them - the covalent bond. They share the electrons in a way that gives a stable Noble Gas electron arrangement.
(c) METALLIC BONDING isn't quite like ionic or covalent bonding, the metal atoms form positive ions, but no negative ion is formed from the same metal atoms, but the positive metal ions/atoms are attracted together by the free moving negative electrons between them. NOBLE GASES are very reluctant to share, gain or lose electrons to form a chemical bond. They are already electronically very stable. For most other elements the types of bonding and the resulting properties of the elements or compounds are described in detail in Parts 2 to 5. In all the electronic diagrams ONLY the outer electrons are shown.
New bonds formed! Lots of energy released Ionic Bonding Poem - a snippet of chemistry 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
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(atomic number) electron arrangement
Poetry in motion!
