Inorganic - 6.1 - Shapes And Molecules Flashcards
Linear bonding
- 180
- 2/0
Non - linear
- 104.5
- 2/2
Pyramidal
- 107
- 3/1
Trigonal planar
- 120
-3/0
Tetrahedral
- 109.5
- 4/0
Octahedral
- 90
- 6/0
Examples of shapes
- linear = CO2
- nonlinear = H2O
- trigonal planar = BF3
- pyramidal = NH3
- tetrahedral = CH4
- octahedral = SF6
How to make structure of poly atomic ions
Always start with double bonds and see where dative bonding could take place
Nitrate ion shape
Trigonal planar
Sulphate ion shape
Tetrahedral
Carbonate ion shape
Trigonal planar
Phosphate ion shape
Tetrahedral
Ammonium ion shape
Tetrahedral using DATIVE bonding
What is a dipole
The separation of charges between atoms due to differences in electronegativity causing polarity
How do London forces work
- all polar and non-polar molecules can have as the movement of electrons in the bonding chnages
- this creates a temporary/ instantaneous dipole
- due to its polarity and charge, it will induce a dipole on a neighbouring molecule
- this process continues
Why are London forces weak
Due to their temporary nature, London forces do not last long and with a large magnitude
How can London forces become stronger
The larger the number of electrons (nuclear charges), the stronger the forces induced, this will require a larger amount of energy to overcome and so results in a larger mp/bp
What are permanent dipole-dipole interactions
- only a polar molecule can have this
- when a polar molecule like HCl is around another polar molecule, it will have a force of attraction
- as it is stronger, it requires a larger amount of energy to overcome and so larger mp/bp
What are simple molecules
E.g. H2O, CO2, H2, N2, O2
Bonding in simple molecules
Simple molecules have weak intermolecular forces between molecules and strong covalent bonds between atoms
Properties of simple molecules
Due to weak intermolecular, these are easily overcome with less energy and broken however when changing state only these change. The covalent bonds are much stronger and require a lot of energy to overcome and so usually do not break.
How does non-polar dissolve in non- polar
- the interactions weaken the intermolecular forces (LF) in both and the compound dissolves, forming the LF with each other, so that the energy is conserved
Non polar with polar substances
- the interactions once again break the LF in both, however the permanent dipole-dipole interactions in the polar solvent, are too strong to be broken and so will not allow for solute to dissolve and will not form bonds with each other, making it not conserved
Polar with polar solvents
Both the LF and perm break and once again bonded tog so energy conserved however not always the case
Electric conductivity
- non-polar molecules do not have any free (delocalised) electrons and so will not be able to carry current and conduct
- polar molecules will be able to conduct when molten or aqueous as the ions are free to move and so can conduct
What is hydrogen bonding
Special type of permanent dipole dipole interaction between molecules:
- need electronegative elements - N,O, F
- need to have hydrogen bonded to them
How does hydrogen bonding act
Between the hydrogen atom of a molecule and the lone pair of the electronegative atom
How to draw hydrogen bonding
Must show:
- charges
- lone pair
- dashed line for bond
- linear bond of 180 deg
Unusual properties of water
- ice less dense: when ice is formed, the hydrogen bonds rearrange from liquid to solid. The lattice structure turns into an open tetrahedral shape and structure with many holes. These holes separate and distance the bonds, making them less dense. When ice melts, the lattice collapses and they move closer together
- high mp/bp: water contains LF, perm and hydrogen bonding. These increase in van der waal’s requires a lot of energy to overcome and so significantly higher
- High surface tension and viscous resulting in droplets and insects to walk on pond surfaces
Hydrogen bonding in DNA
À and G - both have purine bases with two ringed structures
T and C - both pyrimidine bases with single ringed structures
Bond enthalpy of all bonds
LF: 1-10
Perm: 3- 25
Hydrogen: 10-40
Covalent: 150-500
When talking about shape of mol
- eprt
- bond angle
- how many b/l
- relate back to question
What is electron pair repulsion theory
- where electrons around central atom determine shape of mol or ion
- due to the repulsion between bonded and lone pairs
- this will change the shape depending on its strength to be arranged as far apart as possible to minimise repulsion
Factors affecting electronegativity
- number of shells (atomic radius) - if electrons are closer to the nucleus with less shells, it will have greater force of attraction
- charge (number of protons) - more opposite charges will attract and pull of e is greater
What is electronegativity
With any covalent bond, there is a force of attraction of nucleus of atom and shared pair of electrons. However, if following the factors, (small period number and high charge), there will be a greater efoa to pull electrons. This pull of attraction for the electrons is electronegativity. And what creates a small partial charge of a dipole
- the ability for an atom to attract electrons in pair in a covalent bond
Polymolecules can have…
Different number of shapes.
Why are molecules polar?
- Mention all dipoles evident
- has/has no symmetrical structure
- dipoles cancel/ reinforce each other
How to determine mp/bp?
- see all forces: covalent, intermolecular, ionic
- see which can be increased - LF with e , perm with e and hydrogen with how many bond
- see structure - if it is giant or repeating or just simple molecule
