HOME PAGE * KS3 SCIENCES * GCSE BIOLOGY CHEMISTRY PHYSICS * ADVANCED LEVEL CHEMISTRY
Advanced Level Chemistry: More on covalent bonding - bond lengths & bond enthalpies
AQA Advanced A level Chemistry Edexcel Advanced A level Chemistry OCR Advanced A level Chemistry A OCR Salters Advanced A level Chemistry B
More on covalent bonding - single, double and triple bond, their length and strength, dative covalent bonds and bond enthalpy trends Extra Notes on Covalent Bonding and Covalent Compounds Doc Brown's A level Chemistry Revision Extra Notes on chemical bonding for advanced A level chemistry students All the advanced A level 'basics' with lots of examples of dot and cross diagrams of ionic bonding, Lewis diagrams, properties of covalent compounds etc. is on a separate page. However, advanced electron notation using s, p and d notation was NOT included, only a brief mention of intermolecular forces/intermolecular bonding. Dative covalent bonds and shapes of molecules were not included. These and other covalent molecules are covered on this page. There are other pages on SHAPES of MOLECULES The formation of a covalent bond In covalent bonds there is a balance between the repulsive forces between the positive nuclei and the attractive forces between the nuclei and the negative electrons between them. The covalent bond is mutual attraction between the nuclei of two atoms and the electrons in between them (+) -- (+). The bond length is determined by the two atoms adopting the position of minimum potential energy. One or more atomic orbitals from each atom overlap so the bonding pairs of electrons are shared between the nuclei.
The 'dot and cross' (Lewis)
electron diagrams only tell part of the story
Dative covalent bond (co-ordinate bond) A dative covalent is formed when the pair of electrons forming the bond are donated by one atom only. This contrasts with the usual covalent bond by each atom of the bond contributing one electron. Examples of dative bond formation 1. Formation of the oxonium ion H3O+ (also known as hydroxonium ion, hydronium ion) H2O(l) + H+(aq)
This reaction happens whenever you dissolve a
soluble acidic substance in water, but the proton can also come from another
water molecule in a self-ionisation process 2H2O(l)
H2O: + H+
2. Formation of the ammonium ion NH4+ NH3(aq) + H+(aq)
This reaction happens when you dissolve ammonia gas in water (the proton comes from the water) or when you react aqueous ammonia solution with any acid.
H3N: + H+
3. Transition metal complexes - dative covalent bonds with ligands The ligands surrounding the central ion of a complex ion donate pairs of electrons to form the ligand-metal ion bond
Single and multiple covalent bonds - representations (a) A molecule with all single covalent bonds (known as a σ bond, sigma bond, C-H and C-C in this case)
(b) Double covalent bond = (σ bonds C-H, and a delocalised pi bond, the C=C bond is a σ bond plus a π bond)
(c) The C=C bond is a σ bond plus π bonding)
(d) Double covalent bond = (σ bond and delocalised π bond)
(e) Triple covalent bond ≡ (σ bond and a double π bond) Alkynes are
unsaturated hydrocarbons with a C Examples:
C2H2,
C3H4,
All the C-H bonds are single σ bonds.
(f) The nitrogen molecule also has a triple bond
:N
triple bond, all the rest have all single σ bonds C-H, C-C, C-Cl, C-O and O-H.
Relating single, double and triple bonds to average bond enthalpies and bond length The average bond enthalpy is the 'typical' energy required to break 1 mole of a covalent chemical bond (but only involving gaseous species). Bond enthalpy is a measure of the bond strength.
Bond length is defined as the distance between the two nuclei of the two atoms bonded together. You find general patterns of decreasing bond length with increasing bond enthalpy - shorter tends to be stronger because the bonding electrons between the nuclei are closer to the nuclei and consequently more strongly attracted. Some examples and several important patterns to spot:
Some Group VII (Group 7/17) Halogens trends in bond lengths and bond enthalpies
Some general observations, most of which relate to smaller radii giving shorter stronger bonds: Halogen molecules X2: From fluorine to iodine the bond length increases and, except for fluorine, the bond enthalpy decreases as the radius of the halogen atom increases with increasing number of filled inner electron shells. Fluorine is distinctly anomalous with a much lower than expected bond dissociation energy, though the bond length fits the general trend. This is explained by the close proximity of the small fluorine atoms causing repulsion between them due to the closeness of the outer electron orbitals. Hydrogen halides HX: From hydrogen fluoride HF(g) to hydrogen iodide HI(g), there is clear trend in increasing bond length and decreasing bond enthalpy. One result is the increasing ease of aqueous ionisation from hydrofluoric acid to hydriodic acid so that the HX(aq) acids become stronger down the group. In fact, hydrofluoric acid HF(aq) is a relatively weak acid but hydrochloric, hydrobromic and hydriodic acids are all very strong. The latter three are so strong in aqueous media you don't really see the difference e.g. from pH readings, but in non–aqueous media the differences can be clearly measured. Halogenoalkanes R3C–X: Based on polarisation of the bond (Cδ+–Xδ–), you might expect the reactivity order with respect to nucleophiles (electron pair donors) attacking the δ+ carbon bond to be R–F > R–Cl > R–Br > R–I as the electronegativity difference decreases from C–F to C–I. However, it is the decreasing bond enthalpies from C–F to C–I that override this polarisation trend giving the reactivity trend R–I > R–Br > R–Cl > R–F. private tuition IB AS A2 advanced level residential student tuition courses pupil resources teacher resources publishing company revision guides published by Amazon Harper Collins Education Letts Lonsdale Revision Guides Heinemann Educational Books publishers catalogue CGP Books Educational Hodder Education Philip Adam publications Nelson Thornes Philip Allan Textbooks examination boards AQA Edexcel OCR sciences higher education secondary school education college science education institutions Science GCE courses Advanced Level A AS A2 level tuition help tutors colleges semesters books revision guides college textbooks university education courses GCE biology GCSE chemistry courses GCE physics university courses medicine biochemistry university medical sciences university chemistry university biology university physics environmental science biomedical physics courses revision books worksheets workbooks practice examination paper questions science seminars university entrance examinations exam tuition science teacher training dative (co-ordinate) covalent bond for AQA AS chemistry, dative (co-ordinate) covalent bond for Edexcel A level AS chemistry, dative (co-ordinate) covalent bond for A level OCR AS chemistry A, dative (co-ordinate) covalent bond for OCR Salters AS chemistry B, dative (co-ordinate) covalent bond for AQA A level chemistry, dative (co-ordinate) covalent bond for A level Edexcel A level chemistry, dative (co-ordinate) covalent bond for OCR A level chemistry A, dative (co-ordinate) covalent bond for A level OCR Salters A level chemistry B dative (co-ordinate) covalent bond for US Honours grade 11 grade 12 dative (co-ordinate) covalent bond for pre-university chemistry courses pre-university A level revision notes for dative (co-ordinate) covalent bond A level guide notes on dative (co-ordinate) covalent bond for schools colleges academies science course tutors images pictures diagrams for dative (co-ordinate) covalent bond A level chemistry revision notes on dative (co-ordinate) covalent bond for revising module topics notes to help on understanding of dative (co-ordinate) covalent bond university courses in science careers in science jobs in the industry laboratory assistant apprenticeships technical internships USA US grade 11 grade 11 AQA A level chemistry notes on dative (co-ordinate) covalent bond Edexcel A level chemistry notes on dative (co-ordinate) covalent bond for OCR A level chemistry notes WJEC A level chemistry notes on dative (co-ordinate) covalent bond CCEA/CEA A level chemistry notes on dative (co-ordinate) covalent bond for university entrance examinations |
Doc Brown's Chemistry |
|
|
best gift deals latest video game release, best gift deals best bargains in shop sales latest pop music releases, best sales deals download free music, latest film releases, best gifts for teenagers latest high street fashion in clothes, fashionable trending in clothing, best gift deals best bargains in shop salesgirls buy clothes, spend a lot of money on clothes, best sales deals shoes, sweets and chocolates, magazines and make-up best gifts for teenagers Boys buy food and drink, computer games best gift deals best bargains in trainers shop sales DVDs and CDs, girls and boys spend a lot of money on credit for mobile phones best sales deals best bargains in shop sales buses and trains to transport them going out best gifts for teenagers best bargains in shoes shop sales Girls spend a lot of money on clothes best gift deals color colour preferences in clothes, cool sunglasses best sales deals boys buy expensive thins like best gifts for teenagers designer sports clothes and trainers, teenagers save for holidays, best sales deals clothes, mobile phones, birthday presents and electronic goods, teenage accessories, Favourite style of jeans. best gifts for teenagers A typical girl’s shopping list includes mobile phone credit deals best shoes gift deals fashionable quality cool airpods, air pods, fashionable clothes best sales deals the most popular favourite sneakers best gifts for teenagers fancy shoes, sweets, chocolates, magazines, best trainers gift deals best bargains in shop sales lip moisturizer best bargains in shop sale slots on make-up, well being, teenage decor decorating their room best sales deals teenagers like LED string lantern lights, best gifts for teenagers beauty products for teenagers, denim jackets, scrunchies coolness, fashionable back packs, typical boy’s shopping list includes mobile credit deals, eating out takeaway food and drinks, what teenagers like to buy in clothes best gifts for teenagers computer games, DVDs, CDs, what teenagers talk about best gift deals what teenagers worry about, what teenagers like to do for fun sports best sales deals what cool things do teenagers buy, resale websites like eBay Teenager best high street shop or best online deals currys pc world argos amazon john lewis dell acer samsung raycon bose sony asus huawei HP microsoft in-ear headphones earbuds ipad desktop computer laptop computer for school college university students latest video games consoles apple iphone google high end mobile phones cell phone bargain smartphone xiaomi oppo high tech products latest fashion in trainers latest fashion in shoes latest fashion in mobile phones cell phones |