6 Electronegativity, Bond Polarity And Intamolecular Forces Flashcards
Describe the covalent bond in a molecule of an element
Each atom has an equal share of the electrons in the bond. It is a 100 % covalent bond
Describe what happens when bonding atoms are different
- nuclear charges different
- atoms may be different sizes
- Shared pair of electrons may be closer to nucleus of one atom
One of the atoms is likely to attract the bonding electrons more
Definition of electronegativity
A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
What is a non polar bond
- bonded pair shared equally between bonded atoms
- atoms have the same or similar electronegativity
- called pure covalent bonds
Eg C-H
What is a polar bond
- bonded electron pair shared unequally between the bonded atoms
- happens when bonded atoms are different and have different electronegativity
- the more electronegative atom has a greater attraction for the bonded pair of electrons
Define permanent dipole
A small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms
What does a polar covalent bond contain
A permanent dipole
What makes a polar molecule a polar molecule
Is not symmetrical and bind dipoles don’t cancel out
Opposite for a non polar molecule ( you can have a non polar molecule with polar bonds)
Define polar molecule
Has an overall dipole when you take into account any dipoles across the bonds
Polar molecules can dissolve ……
Non polar molecules can dissolve ……
Polar molecules
Non polar molecules
What is the scale to measure electronegativity called and when was it invented
Pauling scale in 1932
Factors affecting electronegativity
Nuclear charge- more protons = more attraction between bonding electrons and nucleus
Distance from the nucleus- smaller radius= stronger attraction. Bonding pair closer to nucleus
Electron shielding- less electron shells between nucleus and bonding pair = stronger attraction
What makes a bond a non polar covalent, polar covalent or ionic
NPC= no difference between electronegativity
PC= small difference in electronegativity
I= large difference in electronegativity
What are the ranges in electronegativity that cause the type of bond to change
Roughly
Difference is bigger than 1.7 = ionic
Difference is between 1.7 and 0.5 = polar covalent
Difference is less than 0.5 = pure covalent (non polar covalent)
Explain why electronegativity increase across a period
- atomic radius decreases
- more nuclear charge (protons)
Therefore stronger attraction between nucleus and bonding pair
Explain why electronegativity decreases down a group
- atomic radius increases
- more shielding
Therefore less attraction between the nucleus and bonding pair
What are intermolecular forces
Weak
Interactions between dipoles of different molecules
Caused by weak attractive forces between small dipoles in different molecules
3 types of intermolecular forces and their relative strengths
Weakest London forces
Permanent dipole dipole interactions
Strongest Hydrogen bonding
What are London forces
They exist between all molecules
Weak attractions between small TEMPORARY dipoles in NEIGHBOURING molecules
How do London forces increase in strength
With the number of electrons increasing
What are the only attractive forces acting in non polar molecules
London forces
Permanent dipole dipole interactions
Polar molecules have them
The permanent dipole of one molecule attracts the permanent dipole in another forming a weak permanent dipole-dipole force
Where are hydrogen bonds found
Between molecules containing
- a strong electronegative atom with a lone pair of electrons ( O, N, F)
- a hydrogen atom attached to the O, N or F
The slightly positive hydrogen on one molecule attracts to a lone pair of electrons on a different molecule
Rules for drawing hydrogen bond
Dotted line
From the lone pair to the hydrogen
How does hydrogen bond effect the boiling point of water
Without it it would be much lower and there would be no liquid water on earth
Properties of water
1) ice less dense than water
- H bonds create open lattice- big gaps make it less dense
2) water has high MP and BP
- H bonds are extra forces on top of London forces
3) high surface tension
- due to raft of H bonds
Explain how structure and bonding in bromine accounts for BP being low
- simple molecule
- only contains London forces
- which are weak and easy to overcome by increased kinetic energy
