Properties of Alkanes Flashcards Preview

CHEM - 4.1.1 Basic concepts + Alkanes (4.1.2) > Properties of Alkanes > Flashcards

Flashcards in Properties of Alkanes Deck (8)
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1

Bonding in alkanes

- Alkanes are saturated hydrocarbons containing only carbon and hydrogen atoms joined together by single covalent bonds.
- Single covalent bonds are called sigma bonds (σ) and each carbon atom in an alkane has 4 sigma bonds.
- A sigma bond is a result of the overlap of two 's' orbitals. A sigma bond has 2 electrons that are shared between the bonding atoms.

2

Shape of alkanes

- General formula: Cn H2n+2
- Bond angle: 109.5
- Shape: Tetrahedral

3

Crude oil

- Crude oil is a mixture of alkanes. Oil refineries separate the crude oil into fractions by fractional distillation is a distillation tower.
- Separation is possible because the boiling point of the alkanes are different and they increase as their chain length increases.
- London forces are weak intermolecular forces that can be easily broken, causing alkanes to turn to gas. The greater the intermolecular forcer, the higher the boiling point.

4

Effect of chain length on B.P

- London forces act between molecules that are in close surface contact.
- As chain length increases, there is higher surface area, so more surface contact is possible between molecules. So the no. of London forces increase.
- London forces are also stronger as there are more electrons so a bigger partial negative charge.

5

Effect of branching on B.P

- Branched isomers have lower boiling points compared to straight chain isomers.
- Molecules without branches have more points of contact.
- Therefore branched molecules have fewer London forces.

6

Complete combustion of alkanes

Produces CO2 and H20.
* Number in front of CO2 is the number of Carbons on reactant side.
* Number in front of H20 is HALF the number of Hydrogens on reactants.

7

Incomplete combustion of alkanes

Produces CO and H20.
* Number in front of CO2 is the number of Carbons on reactant side.
* Number in front of H20 is HALF the number of Hydrogens on reactants.

8

Carbon Monoxide

- Colourless, odourless and highly toxic gas.
- Combines irreversible with haemoglobin in red blood cells to form a compound that prevents haemoglobin from transporting oxygen around the body.
- Person can be poisoned without noticing any danger.