Shapes and intermolecular forces

  • Created by: Hindleyc
  • Created on: 16-06-18 20:26
Bonding pairs, Lone pairs and bond angle of Linear shape
2BP, no LP and 180
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Bonding pairs, Lone pairs and bond angle of Trigonal planar
3BP, no LP and 120
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Bonding pairs, Lone pairs and bond angle of Tetrahedral
4BP, no LP and 109.5
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Bonding pairs, Lone pairs and bond angle of Trigonal pyramidal
3BP, 1LP and 107
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Bonding pairs, Lone pairs and bond angle of Bent
2bp, 2 lp, 104.5
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Bonding pairs, Lone pairs and bond angle of Trigonal bipyramidal
5BP, no lp, 120 and 90
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Bonding pairs, Lone pairs and bond angle of octahedral
6bp, no lp and 90
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How do you explain the shape?
1. state BP&LP 2.state e- pairs repel and try to get as far apart possible or to a point minimum repulsion 3. No lp then e- pairs repel equally 4.lp repel more than bp 5. state shape and bond angle
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What do lp do?
reduce bond angle by 2.5
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What are bonding pairs and lone(non-bonding) pairs of electrons?
Charge clouds that repel each other
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What do pairs of electrons in the outer shells of atoms arrange themselves?
As far apart as possible to minimise repulsion
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arrange bp and lp from greatest repulsion to lowest
Lp-Lp>Lp-Bp>Bp-Bp
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What are the most electronegative atoms?
N,O,F and Cl
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What is electronegativity measured on
Pauling scale (0-4)
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What factors affect electronegativity- across period?
Inc across period as no. protons increases and atomic radius decreases as e- in same shell pulled in more.
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Down group?
Decreases down group as distance between nucleus and outer electrons inc and shielding of inner electrons increases
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What are ionic and covalent bonding?
Extremes of bonding types. similar electro-negativities = covalent and large diff1.7< =ionic
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How does a polar covalent bond form?
When elements in bond have different electro-negativities (0.3-1.7)
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What is a polar covalent bond?
When it has unequal distribution of electrons in bond and produced dipole- slight +Ve and slightly -ve ends
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Which is slightly negative end?
End with larger electronegativity in polar compound
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When will a bond not be polar even if individual bonds within a molecule are polar?
In a symmetrical molecule where all bonds identical and no lone pairs
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why?
Individual dipoles on bonds cancel out due to their symmetrical shape of molecule- no net dipole movement so molecule not polar
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What is electronegativity?
Power of an atom to attract the pair of electrons in a covalent bod/ relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself
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What will the electron distribution in covalent bond between elements with different electro-negativities be like?
Unsymmetrical - produces polar covalent bond and may cause molecule to have a permanent dipole
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What do Van Der Waals forces occur between? what are they not in?
All molecular substances and noble gases. not in ionic substances (all simple covalent molecules and separate atoms in noble gases.)
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What are the electrons in any molecule doing? what does this do?
Constantly and randomly moving. Causes electron density to fluctuate so parts of molecule become more or less -ve =temporary dipole
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What can these instantaneous dipoles cause ?
dipoles to form in neighbouring molecules - induced dipoles opposite sign to original
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What is the main factor affecting Van Der Walls
More electrons there are in a molecule the higher chance that temporary dipoles will form. Makes v.d.w stronger b/w molecules so bp will be greater
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Other factor
Shape can affect size of v.d.w. longer chain=larger SA of contact b/w molecules for v.d.w to form so strong v.d.w
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Where do permanent dipole-dipole forces occur? what can they occur in addition to?
between polar molecules - they have permanent dipoles and can occur in addition to v.d.w
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What are they stronger than>
V.D.W so compounds have higher bp
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What are polar molecules?
Asymmetrical and have bond where there is a significant difference in electro-negativities between atoms
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Where does hydrogen bonding occur?
In compounds that have a H atom attached to 1 of most 3 electro-negative atoms- Nitrogen, Oxygen and Fluorine which must have available lone pair of electrons
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What is there always a large difference in between the H&NOF atoms
Electo-negativity
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What does H bonding occur in addition to?
V.D.W
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What Is it stronger than?
Other 2 types of I.M bonding
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What is the high bp of water nh3 and and HF caused by?
H bonding
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What else all form H bonds?
Alcohols, carboxylic acids and proteins and amides
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Other cards in this set

Card 2

Front

Bonding pairs, Lone pairs and bond angle of Trigonal planar

Back

3BP, no LP and 120

Card 3

Front

Bonding pairs, Lone pairs and bond angle of Tetrahedral

Back

Preview of the front of card 3

Card 4

Front

Bonding pairs, Lone pairs and bond angle of Trigonal pyramidal

Back

Preview of the front of card 4

Card 5

Front

Bonding pairs, Lone pairs and bond angle of Bent

Back

Preview of the front of card 5
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