12.1 - Properties of alkanes Flashcards Preview

OCR A Chemistry A Level - Chapter 12 > 12.1 - Properties of alkanes > Flashcards

Flashcards in 12.1 - Properties of alkanes Deck (7)
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1

What type of bonds are present in alkanes?

Saturated hydrocabons containing only single covalent bonds

- Each carbon is bonded to 4 other atoms by a single covalent bond called - sigma bonds

2

What are sigma bonds?

Covalent bond - shared pair of electrons
Sigma bond - overlapping of 2 orbitals (each overlapping orbital has one electron so the 2 orbitals have 2 in total)

3

What is the shape and bond angle of an alkane?

Each carbon is surrounded by 4 electron pairs in 4 sigma bonds

- Maximum repulsion between these electron pairs result in 3D TETRAHEDRAL ARRANGEMENT
109.5 DEGREES BOND ANGLE

4

Why can atoms in an alkane rotate freely?

The sigma bonds act as axes of rotation so the shapes are not rigid, (double bonds allow no rotation)

5

How are the alkanes of crude oil separated?

Crude oil has 100s of alkanes which are separated by fractional distillation which shows alkanes have many variations in boiling point

6

What is the effect of chain length on boiling point?

Longer the chain length the higher the boiling point
- This is because there are more London forces between the molecules due to larger surface area of contact, so more energy is needed to break the bonds

7

What is the effect of branching on the boiling point of alkanes?

The more branches there are the less the surface area of contact because the branches get in the way of each other, fewer London forces lowering the bp.