1
Q
MOLECULAR SHAPES
A
- Linear
- Triangular Planar
- Tetrahedral
- Pyramidal
- Bent
2
Q
VSPER THEORY
A
- Valence Shell Electron Pair Theory
- Molecular shape results from repulsion between groups of electrons, both bonding and non-bonding, in the valence shell of the central atom
- Allows valence electron groups to have greatest possible angle of separation
3
Q
LINEAR SHAPE
A
- 1 or 2 groups of electrons
- - 180 angles
4
Q
TRIANGULAR PLANAR
A
- 3 groups of electrons
- 120 angles
5
Q
TETRAHEDRAL
A
- 4 groups of electrons
- 109.5 angles
6
Q
PYRAMIDAL
A
- 4 groups of electrons
- 1 is a lone pair
- Ideal; 109.5
- Actual; 107
7
Q
BENT
A
- 4 groups of electrons
- 2 are lone pairs
- Ideal; 109.5
- Actual; 104.5
8
Q
IDEAL BOND ANGLES
A
- angles that would give all the bonding and non bonding valence electrons the largest equal angle of separation
9
Q
ELECTRONEGATIVITY
A
- measures tendency of an atom to attract electrons
- measured of a scale of 0-4
- atoms of high electronegativity have a greater tendency to attract electrons
- increases from left to right in a period, decreases down a group
10
Q
ELECTRONEGATIVITY AND COVALENT BONDS
A
- atoms of different electrons form a covalent bond
- uneven sharing of a bonding electrons occurs
- happens as shard electrons of bond spend time closer to highly electronegative element
- more electronegative atom develops small NEGATIVE charge
- less electronegative atom develops small negative charge
- covalent bonds like this have a BOND DIPOLE
- greater difference in electronegativity of two CB atoms, the greater the size of the bond dipole
11
Q
POLAR MOLECULES
A
- slight positive and slight negative charged ends - net dipole
- occurs in all molecules with a single bond
- if molecule has several bond dipoles, they can reinforce or cancel out each others effect (depend on strength and direction of individual dipoles)
- able to attract one another due to weak electrostatic attraction DIPOLE DIPOLE FORCES
- dissolve ionic solutes
12
Q
POLARITY
A
- if bond dipoles are of equal size and act in symmetrically opposing directions they cancel out effects, making them have zero net dipole and non polar
13
Q
INTRAMOLECULAR FORCES
A
- strong
- covalent bonds keeps atoms clustered together
14
Q
INTERMOLECULAR FORCES
A
- weak
- forces between molecules keeps them bonded
- easily overcome; melting, boiling, evaporating
- covalent bonds between atoms not affected
- only chemical changes affect bonds
15
Q
DIPOLE DIPOLE
A
- increase melting and boiling points
- can be seen that substances with polar molecules have higher melting and boiling points
16
Q
SOLUBILITY
A
- affected by intermolecular forces
- polar substances will be soluble in one another but not soluble in non polar substances
17
Q
ION DIPOLE FORCE
A
- due to attract between dipole of polar molecule and ions charge
- not a type of intermolecular force
18
Q
DISPERSION FORCES
A
- occur in all molecules
- weak for molecules with few electrons
- show increasing strength with greater number of electrons
- effect seen in NON POLAR; alkane family, where boiling point increases with molar mass
- dispersion forces arise when random motion of electrons within molecular produce temporary dipoles
- induced dipoles; temporary dipoles in polar molecules cause close molecules to form this
19
Q
INDUCED AND TEMPORARY DIPOLES
A
- molecule with temporary dipole and induced dipole experience weak electrostatic attraction; dispersion forces
- attractive forces are in a state of rapid change as the temporary and induced dipoles constantly form, rapidly disappear and reform elsewhere
20
Q
HYDROGEN BONDING
A
- Hydrogen bonds are directional intermolecular forces
- occur in molecules have an H-F, H-O or H-N arrangement
- Hydrogen bond is due to the electrostatic attraction between a LONE PAIR of electrons (neg) of an F, O or N atom and an H atom already covalently bonded to another F, O or N atom
- HB described as a form of EXTREME DIPOLE-DIPOLE ATTRACTION; strong positive dipole of an H atom; one bonded to a HIGHLY ELECTRONEGATIVE F, O or N atom is attracted to a strongly negative dipole of F, O or N atom
- Lone pair of electrons of the F, O or N atom and the H atom that form the HB can be part of the same molecule or different molecules
21
Q
MELTING AND BOILING POINTS
A
- For a molecular substance to melt or boil, must overcome the attraction between its molecules (intermolecular forces)
- Heating substance provides the energy to do so
- Intermolecular forces present within a substance increase strength, so does its melting and boiling point
- All molecular substances can interact by dispersion forces – then as a molecular mass increases there is an increase in melting and boiling points of substances
- Effect can be seen in any group of similar molecular compounds where molecular size varies
- Substances that can also interact by dipole-dipole forces will have HIGHER melting and boiling points; compared to other substances of similar molecular size that cant interact this way
22
Q
INTERMOLECULAR FORCES AND SOLUBILITY
A
- Solubility of different substances is greatly affected by the type of INTERMOLECULAR FORCES acting within the substance
- Substances whose molecules attract by similar types of intermolecular forces will be soluble in one another
- Non Polar substances which interact strong by dispersion forces will be soluble in other non polar substances that also interact by dispersion forces
- Compounds that attract strongly by HYDROGEN BONDING are extremely soluble in other compounds that too do this
23
Q
VAPOUR PRESSURE
A
- Vapor pressure; tendency of a substance to evaporate and is measured in kPA
- When a substance evaporates its molecules must escape the intermolecular forces keeping it in the liquid phase
- Weak intermolecular forces correspond to liquids that easily evaporate and have high vapor pressure
- All substances show a greater tendency to evaporate with increasing temperature, so their vapor pressure also increases
- Higher temperature = higher average molecular KE to enable molecules to escape their intermolecular forces of attraction
- For a given temperature the substance with the weakest intermolecular forces, ether has the highest vapor pressure whilst water with the stronger intermolecular forces has the lowest vapor pressure
24
Q
BOILING AND MELTING OINTS OF WATER
A
- Physical properties of water are considered to be unique among molecular substances
- Consists of small particles with weak dispersion forces, its strong polarity and capacity for hydrogen bonding dictate its physical properties
- Water has high melting and boiling point (O and 100) because of the ability of water molecules to form hydrogen bonding with neighboring molecules that compensates for weak dispersion forces
25
PHYSICAL PHASES OF WATER
- - Waters density in the solid phase is less than in the liquid phase
- When it freezes it undergoes major expansion and density drops
- Reduced density of the solid explains why ice floats
- Most substances are denser in the solid phase
26
WHY WATER HAS UNIQUE PROPERTIES
- occurs because waters regular crystal lattice of ice that forms when water freezes
- must allow for each water molecule to form 4 HYDROGEN BONDS with 4 neighbouring molecules
- maximises hydrogen bonding but takes up space
- liquid phase there is less hydrogen bonding
27
WATER HIGH SURFACE TENSION
- shown by liquids tendency to resist any increase in its surface area
- gives water stretchy surface skin appearance that wants to contract
- causes water to from spherical droplets and allows certain insects to scamper across
- result of strong intermolecular forces
- water surface there is an imbalance of these forces causing surface molecules to be pulled inwards to the bulk of the liquid
- consequence, surface is trying to contract and achieve a minimum area
