Which Characteristic Relates to Alkenes, but Not the Other Hydrocarbon Families?

ALKENES - construction & chemical properties

Md Brown's GCSE/IGCSE/O Level KS4 science�CHEMISTRY Revision Notes - Oil, useful products, environmental bug, introduction to organic chemical science

5. ALKENES � unsaturated hydrocarbons � their construction and chemical reactions

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Examples of ALKENES

The lower displayed formulae are a more accurate representation of the construction of the alkene molecules

Revision notes on alkenes in chemistry, physical properties of alkenes, uses of alkenes, chemical reactions of alkenes, help when revising for AQA GCSE chemistry, Edexcel GCSE chemistry, OCR GCSE gateway science chemistry, OCR 21st century scientific discipline chemistry GCSE ix-1 chemistry examinations.

5a. The structure and names of the ALKENE hydrocarbons (unsaturated) Alkenes are a family of hydrocarbons containing at least i covalent carbon...carbon double bond (>C=C<) also as the single bonds formed between carbon and carbon (C-C) and carbon and hydrogen (C-H). The C=C double bond is called the functional group of the homologous serial we call alkenes. Note that the name of all alkene hydrocarbons ends in ...ene eg , ethene, propene, justene etc. All alkenes have single C�H bonds, and from propane onwards, C�C single bonds likewise as the characteristic functional group C=C bail. Reminder: A hydrocarbon, eastward.m. an alkene, can only consist of carbon and hydrogen atoms. If another type of atom (element) is present in the molecule it cannot exist a hydrocarbon due east.g. alcohols, esters and carboxylic acids contain oxygen atoms. A lkenes are another homologous series of organic compounds with the general formula CnH2n where n = 2, three, 4 etc. giving the formulae CtwoH4 , CiiiH6 , C4H8 etc. A homologous series is a family of compounds which take a general formula ( CnH2n for alkenes) and have similar chemical backdrop considering they have the same functional group. In the full general formula n = number of carbon atoms in the alkane molecule (northward = two, 3, 4 etc.) and from the general formula you tin deduce the number of hydrogen atoms, hence the complete molecular formula for ANY alkene with a carbon chain containing one double bond only. This general formula simply applies to hydrocarbon alkenes with one C=C double bail. The carbon - carbon double bail (>C=C<) is referred to as the functional group of the alkenes. The functional group is a group atoms common to all members of a homologous series that confer a item set of characteristic chemic reactions on each fellow member of the series. This ways you tin not only predict the formula of an alkene, but you tin can besides predict their possible chemic reactions and the outcome i.eastward. the products. The three alkene formula quoted to a higher place match the three names above. As with naming all organic molecule series in alkenes eth.. means two carbon atoms in the concatenation, prop... means 3 and merely.. means 4 etc. In the full general formula, n = number of carbon atoms in the alkene molecule (n = two, 3, iv etc.) and from the full general formula you can deduce the number of hydrogen atoms, hence the complete molecular formula for Whatsoever alkene. See section eight. or more than on homologous series and the multifariousness of organic compounds Alkenes are chosen unsaturated molecules considering two atoms can join onto one-half of the carbon = carbon double bond when it opens upwards. In other words they potentially have spare bonds to link up with other atoms and alkanes cannot do this. The word unsaturation implies the fact that the carbon atoms are not bonded to the maximum number of atoms they tin be. Alkenes have ii fewer hydrogen atoms than alkanes. Alkanes are described every bit saturated because they have no C=C double bond and atoms cannot add to them. like in the bromine h2o test described beneath. ie 2 atoms can join onto the 2 atoms of the carbon�carbon double bond in alkenes. C=C + X�Y ==> X�C�C�Y though when studying and writing the structural/displayed formula equations, make certain each carbon atom forms a full of four bonds, not 2 or three! The first three in the alkenes series are shown in the department below and are colourless smelly gases. Examples of alkene structure (1) is the molecular formula: a summary of the totals of each atoms of each chemical element in one molecule (2) is are 'autograph' or 'condensed' versions of the full structural formula or displayed formula (iii) (3) is called the full structural formula or displayed formula: The displayed/structural formula shows how all the atoms are linked with the covalent bonds (the dashes �) ie the C�C bonds and the C�H atom bonds. Note that carbon must class iv bonds (C�C unmarried bond or a C=C double bond) and hydrogen forms ane bond (C�H). It is the presence of the covalent carbon = carbon double bond (C=C) which makes alkenes unsaturated hydrocarbon molecules. More notes on molecules and covalent bonding
Revision notes on alkenes in chemistry, concrete backdrop of alkenes, uses of alkenes, chemical reactions of alkenes, help when revising for AQA GCSE chemistry, Edexcel GCSE chemistry, OCR GCSE gateway science chemistry, OCR 21st century science chemical science GCSE 9-1 chemical science examinations. Examples of the molecular formula, molecular construction of ALKENES
(1), (2), (iii) the C=C is referred to equally the carbon � carbon  'double bond'	ethene
(1), (2a) , (2b) , (iii)	propene
(i), (2) and (butene has 2 possible structures) better shown as but-one-ene and simply-2-ene These two unlike molecular structures for the aforementioned molecular formula are called isomers.	butene
(1) , (ii)	pentene
The total displayed formula for the commencement four members of the homologous series of ALKENES These diagrams evidence ALL the covalent bonds (unmarried C-H, C-C and double C=C) in alkene molecules The formulae tin can also be written as: CH2=CH2, CH3CH=CH2, CHiiiCHiiCH=CH2 and (i) CH3CHiiCHtwoCH=CH2 Note: Just like butene above, there is some other molecule of pentene where the double bond is in another alternative position in the carbon chain: (2) CH3CH2CH=CHCH3 that is, besides as (i) at that place is also (ii) Like with butene, this is some other example of what we call isomers, molecules of different structure with the aforementioned molecular formula, in this case C5H10 . You might not need to know the discussion isomer, but you may need to know these different structures exist, and, exist able to spot them with a spot of atom counting!
another form of C5H10 and below, two examples of Chalf-dozenH12 and The point I'yard making here is that they all have the carbon - carbon double bond (>C=C<) somewhere in the molecule making them an alkene molecule!	other alkenes names not important
The c ovalent bonding diagram for the alkene ETHENE  Two atoms of carbon (2.4) combine with iv atoms of hydrogen (1) to form ethene C2Hfour (only the outer shell of carbon's electrons are shown). And then two electrons from each carbon atom are shared to form the carbon = carbon double bond. The other carbon electrons pair up with a hydrogen electron to brand the single carbon - hydrogen bonds. simplified 'dot and cantankerous' electronic diagram for the covalently bonded ethene molecule Electronically, hydrogen (1 outer electron) becomes like helium (2 outer electrons, full outer shell) and carbon (2.4, 4 outer electrons) becomes like neon (2.viii, full outer shell of 8 electrons), so ALL the hydrogen and carbon atoms effectively take full outer shells in forming the covalent bonds when the atoms share their outer electrons. With only four hydrogen atoms in the ethene molecule, ii carbon atoms must share four electrons to form a double covalent bail (C=C). The molecule can be shown equally  with one carbon = carbon double bail and four carbon � hydrogen unmarried covalent bonds. is the full 'dot and x' electronic diagram for ethene.

Revision notes on alkenes in chemistry, physical properties of alkenes, uses of alkenes, chemical reactions of alkenes, assistance when revising for AQA GCSE chemistry, Edexcel GCSE chemistry, OCR GCSE gateway scientific discipline chemistry, OCR 21st century science chemistry GCSE ix-1 chemistry examinations.

5b. Three important addition reactions of alkenes Alkenes are extremely reactive and important compounds in the chemical industry and are converted into very useful compounds due east.grand. plastics and alcohols. Alkenes are NOT plant in crude oil and must exist made by groovy � thermally breaking down certain fractions from crude oil. Run across C racking crude oil in the petrochemical industry processes A Cracking sit-in! You can demonstrate bang-up in the laboratory by heating alkane grease over an aluminium oxide catalyst at 400�700oC, and collecting the smaller gaseous hydrocarbon molecules over water � easily shown to exist combustible! This experiment needs to exist done as a instructor demonstration � about carefully! Any hydrocarbon liquids collected in the bottle or gases in the inverted test tube should decolourise bromine water � the test for alkenes. For more on nifty and its importance see CRACKING - a problem of supply and demand Important comparison: Unsaturated alkenes are much more reactive than alkanes considering of the reactivity of the carbon = carbon double bond (saturated alkanes have no double bonds) . In these addition reactions unsaturated alkenes form a new bonds either side of the original double bond and therefore class a saturated compound (no longer has a C=C double bond) Yous can think of the double bond as half opening upward and a bond breaking in the added molecule and ii new bonds grade east.one thousand. Once two atoms are joined by the two new single covalent bonds, the double C=C bond no longer exists, it would so exist described as a saturated molecule - cannot add any more atoms to it.
Reaction one. Addition of bromine A examination to distinguish between ALKANE and ALKENE hydrocarbons
	What is a simple test for an alkene? Hydrocarbons are colourless . Bromine dissolved in h2o or trichloroethane solvent forms an orange (yellow/brownish) solution. When orangish bromine solution (bromine water) is added to both an methane series or an alkene the consequence is quite different. The alkane solution remains orange � no reaction. Still, the alkene decolourises the bromine equally it forms a colourless dibromo�alkane compound � see the word and balanced symbol equations below.
ethene + bromine ====> ane,2�dibromoethane .... or CHii=CHii + Br2 ====> Br�CH2CHii�Br or better colour of mixture changes from orange to colourless	Alkenes are unsaturated molecules, atoms tin add together to them via the C=C double bond, so a reaction occurs. The double bond opens up and new carbon � bromine bonds (C�Br) are formed. This double bond makes alkenes much more than reactive than alkanes, the bromine water test for alkenes is just 1 example. Alkanes are saturated � no double bond � and atoms cannot add � so no reaction.
propene + bromine ====> 1,two�dibromopropane .... or CH3CH=CHtwo + Br2 ====> CHiii�CHBr�CHtwoBr or better	2nd example of bromine addition to a double bond giving a saturated dibromo compound. The decolourisation of bromine is a unproblematic and effective chemical exam for an alkene � an unsaturated hydrocarbon. The same reaction happens with chlorine (just but Cl instead of Br) This reaction is NOT given by alkanes because they do NOT have a carbon = carbon double bond.
a justene + bromine ====> a dibromobutane + Br2 ====> + Br2 ====>	The addition of bromine to the ii butenes giving two slightly different dibromobutanes. Note again y'all have gone from an unsaturated alkene (can add atoms to it) to a saturated derivative of an alki (cannot add atoms to information technology)
Reaction two. Alkenes can add hydrogen to class a saturated alkane molecule
CHthree�CH=CHii + H2 ====> CH3�CH2�CHiii H2 propene + hydrogen ===> propane	Alkenes will react with hydrogen gas over a nickel goad. The respective saturated alkane is formed. Addition of hydrogen is the reaction process is used to make margarine from vegetable oils.
Reaction 3. Addition of water to alkenes to make alcohols
ethene +water ===> ethanol CHii=CHtwo + H2O ===> CH3�CH2�OH + H2O ===>	eg the alcohol ethanol can be made by passing ethene gas and h2o vapour (steam) over an acid catalyst at 300oC. The higher boiling ethanol and unreacted h2o tin can be condensed out equally liquids and very low boiling ethene gas recycled through the reactor and the ethanol purified past fractional distillation. This is an instance of an improver reaction and a hydration reaction because information technology involves the addition of water to another molecule. run across Alcohols, Ethanol, manufacture for more details of the process
For (iv) Polymer formation � Polymerisation See Part seven. Polymers�Plastics section and Part 11. More on addition polymers and condensation polymers Revision notes on alkanes in chemistry, physical backdrop of alkenes, uses of alkenes, chemic reactions of alkenes, aid when revising for AQA GCSE chemical science, Edexcel GCSE chemical science, OCR GCSE gateway scientific discipline chemistry, OCR 21st century science chemistry GCSE ix-ane chemical science examinations.

5c. More on ALKENES � unsaturated hydrocarbons � and quick summary too

• Alkenes cannot be obtained directly from crude oil and must be made past bully (meet section 6 bang-up notes).
• The unsaturated hydrocarbons grade an homologous series chosen alkenes with a general formula C_northwardH_2n
  • Unsaturated ways the molecule has a C=C double bail to which atoms or groups tin add.
• Alkene examples: Names end in ...ene
  • ethene
  • propene
  • butene
• The alkenes are more reactive than alkanes considering of the presence of the carbon = carbon double bail which is relatively easily partially broken.
  • Therefore, alkenes readily undergo addition reactions in which one of the carbon = carbon double bonds breaks allowing each carbon atom to course a covalent bond with another atom such equally hydrogen or bromine.
  • In alkanes all the C�C and C�H single bonds are very strong and not easily broken to permit the alkane molecule to readily undergo a chemical change
• Examples of addition reactions are : with hydrogen under pressure level and in the presence of a nickel catalyst to form an alkane

  • + H₂ ====>

    • ethene + hydrogen ====> ethane

  • + H₂ ====>
    • propene + hydrogen ====> propane
• Alkenes react by 'addition' with bromine and decolourises the orange bromine h2o because the organic production is colourless, and this is a simple examination to distinguish an alkene from an alkane.
  • run into above equations for ethene and propene
• Vegetable oils contain unsaturated fats (not hydrocarbons) and tin be hardened to form margarine by adding hydrogen on to some of the carbon=carbon double bonds using a nickel goad.
  • The procedure is called hydrogenation,
  • and the modify in an 'unsaturated' part of an oil molecule is
  • �CH=CH� + H₂ ====> �CH₂�CH_ii�
  • and so producing a 'saturated' section in the molecule.
  • S tructure of 'fatty' saturated/unsaturated/hydrogenated�fats�oils and uses are described in section xiv.

• Alkenes add water to make alcohols e.1000.

  • ethene +water ===> ethanol (synthetic 'alcohol')
  • CH_two=CH_ii + H_twoO ===> CH₃�CH₂�OH
• Alkenes can add to themselves by improver polymerisation to form 'plastic' or polymeric materials.
  • 
  • For more details meet section 7. Polymers�plastics notes
• Alkenes readily burn, but like alkanes, to give carbon dioxide and water if combustion is complete e.g.
  • consummate oxidation = complete combustion
  • alkene hydrocarbon + oxygen ===> carbon dioxide + water
  • ethene + oxygen ====> carbon dioxide + h2o
    • C₂H_iv + 3O₂ ====> 2CO₂ + 2H₂O
  • propene + oxygen ====> carbon dioxide + water
    • C₃H_vi + four^one/₂O₂ ====> 3CO_two + 3H_iiO
    • or 2C₃H₆ +9O_ii ====> 6CO₂ + 6H₂O
  • However, they are NOT used as fuels for two reasons.
    1. They are far too valuable for use to make plastics, anti�freeze and numerous  other useful compounds.
    2. They burn with a more smoky flame than alkanes due to less efficient, and more polluting incomplete combustion, and so the oestrus energy release is lower than for alkanes.
  • Free unburned carbon might be released or merely half-burned to carbon monoxide. The hydrogen will ever be oxidised to water.
    • So, for example, pentene might partially burn as follows ..
    • C₅H₁₀  +  5O₂  ===> 2C  +  CO  + 2CO₂  +  5H₂O
    • ... giving 2 complete combustion products and two incomplete combustion products, smokey!
• Alkenes are isomeric with cycloalkanes eastward.1000. the molecular formula C₆H₁₂ can represent hexene or cyclohexane

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Revision notes on alkanes in chemistry, physical backdrop of alkenes, uses of alkenes, chemical reactions of alkenes, assistance when revising for AQA GCSE chemistry, Edexcel GCSE chemistry, OCR GCSE gateway science chemistry, OCR 21st century science chemistry GCSE 9-1 chemical science examinations.

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Keywords and phrases: The alkenes are a serial of hydrocarbon molecules (fabricated of carbon and hydrogen atoms). They are referred to as 'unsaturated' hydrocarbons considering they have a carbon � carbon C=C double bond and other atoms tin can add to them via unproblematic addition reactions. The physical backdrop and chemical reactions of alkenes with hydrogen (to form alkanes), bromine to form a dibromoalkanes (used every bit a exam for alkenes), polymerisation (cocky�improver of alkene molecules to form polymers like polyethene and with oxygen (combustion, burning) are fully described with give-and-take and symbol equations. These notes on alkenes are designed to meet the highest standards of knowledge and understanding required for students/pupils doing GCSE chemistry, IGCSE chemistry, O Level chemistry and KS4 science courses. These revision notes on the chemical properties reactions and uses of alkenes should show useful for the NEW AQA GCSE chemical science, Edexcel GCSE chemical science & OCR GCSE chemical science (Gateway & 21st Century) GCSE (9�ane), (ix-v) & (five-1) science courses.

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Which Characteristic Relates to Alkenes, but Not the Other Hydrocarbon Families?

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