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Molecular shape depends on what?
It depends on the electron pairs around the central atom.
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Why to electron pairs repel each other?
Because they are negatively charged, so they will repel each other as much as they can.
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Where are the angles the biggest to the smallest between different pairs of electrons.
- Lone-pair/Lone-pair: Biggest
- Lone-pair/Bonding-pair: Second Biggest
- Bonding-pair/Bonding-pair: Smallest
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What is the name given to the type of electron pair effects the angle of the bonds?
Electron pair repulsion theory.
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State the name and angle size of the following molecules:
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State the name, bond angles and the number of lone pairs of the molecule:
- Trigonal Planar
- 120o
- No lone pairs
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State the name, bond angles and the number of lone pairs of the molecule (2 answers):
- Non-Linear or Bent
- 1 Lone Pair (120o) (3 Electron Pairs)
- 2 Lone Pairs (104.5o) (4 Electron Pairs)
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State the name, bond angles and the number of lone pairs of the molecule:
- Tetrahedral
- No lone pairs
- 109.5o
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State the name, bond angles and the number of lone pairs of the molecule:
- Trigonal Pyramidal
- 1 Lone Pair
- 107o
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State the name, bond angles and the number of lone pairs of the molecule:
- Trigonal Bipyramidal
- No lone pairs
- 90o
- 120o
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State the name, bond angles and the number of lone pairs of the molecule:
- Octahedral
- No lone pairs
- 90o
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What is an allotrope?
They are different forms of the same element in the same state.
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How many allotropes does Carbon have and what are they?
Three - Graphite, Diamond and Fullerenes.
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Diamond is made up of carbon atoms. Each atom is ____ bonded with sigma bonds to how many other carbon atoms?
- Covalently
- Four carbon atoms
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In diamond, the atoms arrange themselves in what shape?
A tetrahedral shape.
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Because of diamond's strong covalent bonds, it has the following 5 properties:
- 1: It has a very high melting point. It actually sublimes at over 3800K
- 2: Diamond is extremely hard.
- 3: Vibrations travel easily through the stiff lattice, so it is a good thermal conductor.
- 4: It cannot conduct electricity - all outer electrons are held in localised bonds
- 5: It won't dissolve in any solvent.
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In graphite, carbons atoms are arranged in sheets of flat ____ covalently bonded with __ bonds each.
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In graphite, the fourth outer electron is what?
Delocalised.
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What are the 5 properties of Graphite?
- 1: The weak bonds between the layers in graphite are easily broken so the sheets can slide over each other
- 2: The delocalised electrons in graphite means that it can conduct electricity
- 3: The layers are quite far apart compared to the length of the covalent bonds, so graphite is less dense than diamond.
- 4: It has a very high melting point (it sublimes at over 3900K)
- 5: It's insoluble in any solvent
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What are fullerenes?
They are molecules of carbon shaped hollow balls/tubes. Each carbon atom forms three covalent bonds, leaving free electrons that can conduct electricity. They are nano particles.
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What is C60
Buckminsterfullerene. It has 60 carbon atoms joined to make a ball.
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Many fullerenes are soluble in ___ solvents, and form ___ ___ solutions.
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Because fullerenes are hollow, they can be used to cage other molecules. Why is this useful?
It can be used as a way of delivering a drug into specific cells of the body because it can trap another molecule inside it.
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Nano particles have very different ______ from bulk forms of the same substance.
Properties.
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A carbon nanotube is like...
A single layer of graphite rolled up into a tiny hollow cylinder.
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What are the three properties of nanotubes?
- 1: Very strong because of the covalent bonds
- 2: Can conduct electricity so they can be used as tiny wires in circuits
- 3: The ends of a nanotube can be capped off to create a large molecule cage structure
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Why is there a debate about the safety about nanotechnology?
We do not know if they are safe to use or not. And weighing up any risks against the benefits.
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What type of bonds can be described as purely covalent?
Bonds between atoms of a single element. Such as H2
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The ability to attract the bonding electrons in a covalent bond is called...
Electronegativity.
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Electronegativity is measured using the Pauling scale. What is the most electronegative element?
Fluorine
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In a covalent bond between two atoms of different electronegativities, the bonding electrons are ____ towards the more electronegative atom. This makes the bond ___.
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Some elements such as carbon and hydrogen have pretty similar electronegativities, so bonds between them are essentially...
Non polar
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In a polar bond, the difference in electronegativity between the two atoms causes a ____.
Dipole
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What is a dipole?
A dipole is a difference in charge between the two atoms caused by a shift in the electron density in a bond.
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If the difference in electronegativity is large enough, the bond pretty much becomes...
Ionic
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The greater the difference in electronegativity...
The more polar the bond.
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Some molecules with polar bonds are polar molecules - the molecule itself has a permanent dipole. Whether a molecule itself is polar depends on its...
Shape and the polarity of it's bonds.
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In a simple molecule, such as HCl, the polar bond gives the whole molecule a permanent dipole - it's a...
Polar molecule.
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A complicated molecule may have several polar bonds. If the polar bonds are arranged so they point in opposite directions, they'll ____ each other out - the molecule is __-____ overall.
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If polar bonds all point in roughly the same direction in a molecule, the molecule will then be...
Polar
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Long paris on electrons on the central atom also have an effect on the overall polarity and may ____ out the dipole created by the bonding pair.
Cancel
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The length of a bond is related to its...
Strength
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In covalent bonds, there isn't just an attraction between the nuclei and the shared electrons. Two _____ charged nuclei also ___ each other, as do the ____.
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What is the distance of the bond length?
The distance between two nuclei is the distance where the attractive and repulsive forces balance each other.
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The stronger the attraction between the atoms, the higher the ___ _____ and the ____ bond length. If there's a more attraction, the nuclei will pull ___ together.
- Bond enthalpy
- Shorter
- Closer
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What are the 3 types of intermolecular forces?
- 1: Instantaneous dipole-induced dipole or London forces
- 2: Permanent dipole-dipole
- 3: Hydrogen bonding
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London forces are found between...
All atoms and molecules.
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Electrons in charge clouds, are always ____ really quickly. At any particular moment, the electrons in an atom are likely to be more to one ___ than the other. At this moment, the atom would have...
- Moving
- Side
- Temporary dipole.
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A dipole can cause another temporary dipole in the neighbouring atom. The two dipoles are then...
Attracted to each other.
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In London forces, as the electrons are constantly moving, the dipoles are being ____ and ____ all the time. Even though the dipoles keep changing, the overall effect is for the atoms to be ____ to each other.
- Created
- Destroyed
- Attracted
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Stronger London forces mean higher/lower melting and boiling points.
Higher.
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Not all London forces are the same strength. Larger molecules have larger ____ ____, meaning ____ London forces.
- Electron clouds.
- Stronger.
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Molecules with greater surface areas also have stronger/weaker London forces because they have a...
- Stronger
- Bigger exposed electron cloud.
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When you boil a liquid, you need to overcome the ____ forces so that the particles can escape from the liquid surface. It stands to reason that you need more/less energy to overcome stronger intermolecular forces, so liquids with stronger London forces will have higher/lower melting points too.
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Melting solids also involves _____ intermolecular forces, so solids with stronger London forces will have higher/lower melting points.
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Alkanes have _____ bonds inside the molecules. Between the molecules, there are ____ forces with hold them all together.
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The longer the carbon chain, the _____ the London forces - there's more/less molecular surface area and more ____ to interact.
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Branched chained alkanes have smaller molecular _____ _____ and they can't pack as closely together - so the London forces are ____.
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Long-chain alkanes have higher/lower boiling points than short-chain alkanes.
Higher
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Straight chains alkanes have higher/lower boiling points than branched alkanes.
Higher
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Polar molecules have _____ dipole-dipole forces.
Permanent
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The d+ and d- charges on ____ molecules cause ___ electrostatic forces of attraction between molecules
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What is the experiment used to find out if molecules of a jet of liquid are polar or non-polar?
If you put an electrostatically charged rod next to a jet of polar liquid, like water, the liquid will move towards the rod. Polar liquids contain molecules with permanent dipoles. It doesn't matter if the rod is positively or negatively charged . The polar molecules in the liquid can turn around so the oppositely charged end is attracted towards the rod.
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What is the strongest intermolecular force called?
Hydrogen bonding
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When does Hydrogen bonding only occur?
When H is covalently bonded to F, O or N.
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Why is it that only N, O and F can do Hydrogen bonding and how does it occu
It is because they are very electronegative, so they can draw the bonding electrons away from the H atom. The bond is so polarised, and H has such a high charge density because it's so small that the H atoms form weak bongs wit lone pairs of electrons on the F, N or oxygen atoms of other molecules
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Molecules which have hydrogen bonds are usually _______ containing -__ groups or -__ groups. Water and ammonia both have hydrogen bonding.
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Hydrogen bonding can have a huge effect on the properties of substances. What are these two effects?
They have higher melting and boiling points than other similar molecules because of the extra energy needed to break the Hydrogen bonds.
(This is the case with water, and also HF which as a much higher boiling point than the other hydrogen halides.)
Ice has more hydrogen bonds than liquid water, and H bonds are relatively long. So the H2O molecules in ice are further apart on average, making ice less dense than water.
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For one substance to dissolve into another, three things have to happen. They are:
- 1 - Bonds in a substance have to break
- 2 - Bonds in the solvent have to break
- 3 - New bonds have to form between the substance and the solvent.
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Usually, a substance will only dissolve if the strength of the new bonds formed is the ____ __ or ____ ___, the strength of the bonds that are broken.
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What are the two main types of solvents?
1 - Polar solvents such as water. Water molecules bond to each other with hydrogen bonds.
2 - Non polar solvents such as hexane. Hexane molecules bond to each other by london forces. Many substances are soluble in one type of substance but not the other.
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Ionic substances dissolve in _____ _____ such as ____.
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How do ionic substances dissolve in polar solvents?
- 1 - The ions are attracted to the oppositely charged ends of the water molecules.
- 2 - The ions are pulled away from the ionic lattice by the water molecules, which surround the ions. This process is called hydration.
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Some ionic substances don't dissolve in polar solvents because...
the bonding between their ions is too strong.
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Alcohols also dissolve in ____ ____ such as water.
Polar solvents.
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Alcohols are covalent, but they can dissolve in water, this is because...
the polar O-H bond in an alcohol is attracted to the polar O-H bonds in water. Hydrogen bonds form between the lone pairs of the d- oxygen atoms and the d+ hydrogen atoms.
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The carbon chain part of an alcohol isn't attracted to water, so the more/less carbon atoms there are, the more/less soluble the alcohol will be.
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Not all molecules with polar bonds dissolve in water. What are these molecules?
Halogenoalkanes
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Why don't halogenoalkanes dissolve in water?
Although they contain polar bonds, their dipoles aren't strong enough to form hydrogen bonds with water.
The hydrogen bonding between water molecules is stronger than the bongs that would be formed with halogenoalkanes, so they don't dissolve.
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Non-Polar substances dissolve best in non-polar solvents. Why is this?
Non polar substances such as ethene have London forces between their molecules. They form similar bonds with non-polar solvents such as hexane - so they tend to dissolve in them.
Molecules of polar solvents such as water are attracted to each other more strongly than they are to non-polar molecules such as I2 - so non polar substances don't tend to dissolve easily in polar solvents.
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Substances usually dissolve best in solvents that have ____ bonds.
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