DF - bonding and structure *01 *02

Question 1

what bonds are in organic molecules

Answer 1

single bonds - sigma bonds (σ)

double bonds - pi bonds (π)

Question 2

describe a sigma bond (σ)

Answer 2

This is a single covalent bond
Formed when two orbitals overlap, in a straight line, in the space between two atoms
Gives the highest possible electron density between the two +ve nuclei so sigma bonds usually quite stong

Question 3

What orbital can form a sigma bond (σ)?

Answer 3

Any orbital can form a σ bond as long as they point towards the other atom
So you can get σ bonds made from 2 s orbitals, 2 p orbitals, 1 s orbital and 1 p orbital

Question 4

Describe a double bond

Answer 4

double bonds are made up of a sigma (σ) bond and a pi (π) bond

Question 5

Describe a pi bond (π)

Answer 5

a π bond is formed when two p orbitals overlap sideways.

- has two parts, one above and one below molecular axis because p orbital are dumbbell shaped

Question 6

what is stronger? - sigma bond (σ) or pi bond (π)

Answer 6

a pi bond is weaker than a sigma bond

- this means a double bond (σ+π) is less than twice as strong as a single bond

Question 7

what explains the shape of molecules?

Answer 7

electronic repulsion

1. the shape of a molecule depends on the electrons in the outer shell of the atoms involved
2. electrons repel each other so molecules take the shape that allows all the pairs of electrons to get as far away from each other as possible

Question 8

Shape of single-bonded carbon atoms?

Answer 8

Tetrahedron

• 4 areas of electron density
• all bonding pairs
• bond angle between any two covalent bonds is 109.5degrees
• 3-D shape so drawn with wedges (out of page) and dotted lines (into page)

Question 9

Shape of atoms around a double-bonded carbon atom?

Answer 9

Equilarteral triangle

• planar (flat) molecule because of C=C bond, little rotation
• all bond angles are 120degrees
• each double-bonded carbon atom and the atoms attached to it are said to be trigonal planar, the attached atoms are at the corners pf an imaginary equilateral triangle
• if any organic groups bonded to C=C bond they are not planar. So, propane - CH3CHCH2 the CH3 isn’t planar