Shapes Of Molecules And Ions Flashcards
2 areas of electron density
Linear : 180°
2 areas of electron density w/ 2 lone pairs
Non-linear : 104.5°
3 regions of electron density
Trigonal planar : 120°
3 regions of electron density w/ 1 lone pair
Pyramidal : 107°
4 areas of electron density
Tetrahedral - 109.5°
5 areas of electron density
Trigonal bypyramidal - 90° & 120°
6 areas of electron density
Octahedral - 90°
Wedges: solid line
In the paper
Wedges: solid wedge
Coming out of paper
Wedges: dotted wedge
Going into paper
Electron pair with strongest repulsion
Lone pair - lone pair
Electron pair with weakest repulsion
Bonding pair - bonding pair
How does a lone pair affect the bond angle
Reduces it by 2.5° for each lone pair
Explain the trend of in the melting points of the halogens as you move down group 7 (3)
- melting points increase down group 7
- greater number of electrons
- so induced dipole-dipole interactions are stronger
Explain why each bond angle in BH3 is 120° (2)
- boron has 3 bonding pairs of electrons
- which repel each other equally
Explain how the C-H bond differs from the N-H bond in terms of bond polarity (2)
- N-H bond more polar than C-H
- as difference in electro negativity between nitrogen and hydrogen atom is larger
Define: electronegativity (2)
- the ability of an atom to attract electrons
- in a covalent bond
State whether HCONH2 is a polar molecule (3)
- polar
- because polar bonds present
- unsymmetrical distribution of charge
What is the meaning of δ+ (1)
Partial positive charge
State which property of atoms causes a bond to be polar (1)
Electronegativity difference
Which compound isn’t influenced by a lone pair of electrons?
BF3
What compound has a shape that is influenced by lone pairs around the central atom?
ClF3
State how two carbon atoms form a carbon-carbon bond in graphene (1)
Shared pair of electrons
Empirical formula of graphene
CH
Explain why a CH2Cl2 molecule is polar (1)
The molecule is non-symmetrical
Predict and explain shape of the AlH4- ion (3)
Shape : tetrahedral
Explanation :
- equal repulsion
- b/w 4 bonding pairs
Why does electronegativity increase as you go up the group?
Because there’s less shells so less shielding -> electrons are attracted more easily
How do lone pairs affect polarity
Lone pair:
- non-symmetrical
- polar
No lone pair:
- symmetrical
- non-polar (dipoles cancel out)
What molecules are never polar
Hydrocarbons
Estimate the H-O-H bond angle in water using electron pair repulsion theory (3)
- 104.5°
- 4 areas of electron density
- extra repulsion due to lone pairs
Suggest a way that the bond angle in NH3 could become 109.5° (3)
- Nitrogen can form a dative bond
- therefore no longer any lone pairs
- so no extra repulsion
Minimum and maximum number of electrons in outer shell of sulfur (2)
Min = 8
Max = 18
Predict if the SF6 molecule is polar and explain why. (2)
- non polar
- no overall dipole
Explain why the C-F bond does not readily break (2)
- C-F bond is stronger
- and more polar
Predict and explain if halogens can conduct electricity in any state (2)
- do not conduct in any state
- as there’s no delocalised electrons
Order the three main types of intermolecular forces in ascending order of strength (3)
- induced dipole-dipole
- permanent dipole-dipole
- hydrogen bonding
Identify the strongest intermolecular force between:
i) methanal molecules
ii) methanoic acid molecules
iii) water and methanal
iv) water and methanoic acid
i) permanent dipole-dipole forces
ii) hydrogen bonding
iii) hydrogen bonding
iv) hydrogen bonding
Explain why sodium methanoate is solid at room temp and methanoic acid is a liquid (3)
- sodium methanoate is ionic
- methanoic acid is a simple covalent substance
- ionic bonds are stronger
Explain why the boiling point of H2O does not follow the Group 6 boiling point trend (2)
- water is able to form hydrogen bonds between molecules
- hydrogen bonds are the strongest intermolecular forces
Explain how physical properties of ammonia allow it to be easily separated in the Haber process (2)
- boiling point of ammonia higher than that of hydrogen and nitrogen
- mixture of gases can be cooled so ammonia condenses first
Explain why intermolecular forces between water molecules are stronger than those b/w ammonia molecules (4)
- oxygen has a greater mass
- so stronger dipole-dipole interactions
- water can form more hydrogen bonds per molecule than ammonia
- as there’s 2 lone pairs of electrons on oxygen but only 1 on nitrogen
Explain why the bond angle in NH3 is different to that of BH3 (2)
- lone pairs of electrons on N have greater repulsion
- so pairs of electrons arrange themselves as far apart as possible to minimise repulsion
Explain why CCl4 is non-polar but CH3Cl is polar (3)
- C-Cl bond is polar
- CCl4 is a symmetrical molecule
- polarity of C-Cl bonds cancel out in CCl4
Explain whether B-Cl bond or B-H bond is more polar (4)
- B-Cl = covalent bond
- formed by shared pair of electrons between B and Cl atom
- B-H bond less polar than B-Cl bond
- as difference in electronegativity in B-H is smaller
Predict whether the b.p of CH4 is lower than the b.p of CCl4 (4)
- lower than CCl4
- bcs CCl4 has more electrons
- therefore stronger London forces in CCl4
- so more energy required to break intermolecular forces b/w CCl4 molecule
Predict whether each is polar or non polar: (3)
- OF2
- PF3
- BCl3
- OF2 = polar
➡️ bond polarities DON’T cancel out - PF3 = polar
“ “ - BCl3 = non-polar
➡️ bond polarities DO cancel out
Explain why ice has a density lower than liquid water (2)
- water molecules in ice spread further away
- hydrogen bonding between water molecules causes ice to have this anomalous density
Explain why the m.p of water is higher than that of phosphine (3)
- water has hydrogen bonds
- phosphine has permanent dipole-dipole forces
- hydrogen bonds require more energy to overcome
Compare the bond angles in F-C-F and
F-N-F (5)
F-C-F:
- 120°
- due to 3 areas of electron density around carbon
F-N-F:
- 107°
- due to 4 areas of electron density around nitrogen
- extra repulsion from unbonded pairs
Explain difference in molecular polarity in tetraflourohydrazine and tetrafluoroethene (4)
- C-F and N-F bonds are both polar
- but C2F4 is a symmetrical molecule
- so bond polarity in C2F4 cancels out
- N2F4 is an unsymmetrical molecule
Explain why methanol is soluble in water (3)
- O-H bond = polar
- methanol can form H-bonds with water
- H-bonding with water increases solubility
Predict whether alkanes are soluble in either water or propanone (5)
- insoluble in water
- soluble in propanone
- non-polar molecules
- dont form h-bonds with water
- form more London forces w/ propanone
Explain why iodine vaporises easily (2)
- weak induced d.p - d.p interactions between molecules
- these weak forces are easily overcome
Explain the difference in electrical conductivity of sodium chloride and iodine (3)
- iodine has no free electrons to carry charge
- molten NaCl has ions which are free to move
- solid NaCl has no free ions as they’re fixed in position therefore NaCl cannot conduct when solid
