Chapter 6 Shapes of Molecules and Intermolecular Forces
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What is Electron-Pair repulsion theory
Pairs of electrons around a central atom repel each other, so they move as far apart as possible to minimise this repulsion. This means molecules containing 3 or more atoms have shapes
What is the molecular shape and bonding angles for: 2 pairs of electrons (or 2 regions of electron density) repelling around a central atom
Linear 180°
When working out shapes, how many regions of electron density do double and triple bonds count as
1
What is the molecular shape and bonding angles for: 3 pairs of electrons around a central atom
Trigonal Planar 120°
What is the molecular shape and bonding angles for: 4 bonding pairs around a central atom with no lone pairs
Tetrahedral 109.5°
What is the molecular shape and bonding angles for: 4 pairs of electrons around a central atom with 1 lone pair
Pyramidal 107°
What is the molecular shape and bonding angles for: 4 pairs of electrons around a central atom with 2 lone pairs
Non Linear 180°
What is the molecular shape and bonding angles for: 5 pairs of electrons around a central atom
Trional Bipyramid 90° 120°
What is the molecular shape and bonding angles for: 6 pairs of electrons around a central atom
Octahedral 90°
By how many degrees is the bond angle reduced for each lone pair
2.5°
Define Electronegativity
Electronegativity is a measure of the ability of an atom in a molecule to attract a pair of electrons in a covalent bond to itself
Finish this sentence: The higher the electronegativity value…
The more strongly the bonding electrons are attracted to that atom
Going up a group does electronegativity increase or decrease
Electronegativity increases up a group
Across a period, does electronegativity increase or decrease
Electronegativity increases across a period (up to group 7)
What is the most electronegative atom
Fluorine
What group on the periodic table has the least electronegative atoms
1
Which elements have the most electronegative atoms
• Nitrogen • Oxygen • Fluorine • Chlorine
What happens to the pull on bonding electrons as nuclear charge increases
It increases
Why does the pull on bonding electrons decrese further from the nucleus
Pull falls rapidly as electrons become further from the nucleus and the number of shielding inner shells increases
What is a non-polar bond
In a non-polar bond, the bonded electron pair is shared equally between the bonded atoms
When is a bond non polar
• The bonded atoms are the same • The bonded atoms have the same, or similar, electronegativity values.
What is a polar bond
In a polar bond, the bonded electron pair is shared unequally between the bonded atoms
When is a bond polar
A bond will be polar when the bonded atoms are different and have different electronegativity values, resulting in a polar covalent bond
Why is H–F a polar bond
In H-F, F has a higher electronegativity than H so the bonding electrons are more attracted to the F end of the bond. The bond is polarised