DF - bonding and structure *01 *02 Flashcards
what bonds are in organic molecules
single bonds - sigma bonds (σ)
double bonds - pi bonds (π)
describe a sigma bond (σ)
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
What orbital can form a sigma bond (σ)?
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
Describe a double bond
double bonds are made up of a sigma (σ) bond and a pi (π) bond
Describe a pi bond (π)
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
what is stronger? - sigma bond (σ) or pi bond (π)
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
what explains the shape of molecules?
electronic repulsion
- the shape of a molecule depends on the electrons in the outer shell of the atoms involved
- 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
Shape of single-bonded carbon atoms?
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)
Shape of atoms around a double-bonded carbon atom?
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