In a way you could compare this chapter to Assassin's Creed, you read the question and as soon as the answer flies past you, you attack it and stab it to the page so it stays there, or maybe that's just me.
Coming up: Some definitions.
IONIC BONDING: The electrostatic attraction between oppositely charged ions.
You may need to construct a "dot and cross" diagram to show this. Simply figure out which atom will lose an electron and which one will gain that electron (or more). The one which lost the electron has a charge of +1 the one which gained the electron will have a charge of -1. Now you all know that opposite charges attract so these ions also attract to form a compound.
Now draw the positive ion with an empty shell (or a lower shell that is full), brackets round it and a charge of +1 and next to it draw a diagram of the -1 ion with its own electrons as crosses and the extra electrons as circles (or visa versa). Don't forget the brackets!
It's quite wordy to explain it but it is very simple in practise, quite literally free marks in the exam.
Example: A reaction between Magnesium and chlorine. The magnesium loses two electrons to have a full outer shell and chlorine needs 1 electron each to have a full outer shell (so two chlorine atoms required). The magnesium donates the 1 electron to each chlorine and they become ions. Chlorine with -1 charge each and Magnesium with +2 charge.
You are required to know the formulae of the following ions:
NO3: -1
CO3: -2
SO4: -2
NH4: +1
COVALENT BOND: Shared pair of electrons.
Unlike in ionic bonding, during covalent bonding the electrons are shared, not given away. This forms a bond equal in strength to ionic bonding. However covalent bonding occurs between non metals, whilst ionic bonding occurs between metals and non metal (except hydrogen and a non metal).
It is also important to note that a covalent bond is directional (acting only between the two atoms involved in the bond) whilst ionic bonding attracts in all directions (often forming a lattice - Like a net).
Here is a good guide on how the bonds are formed. The individual atoms have only one role is life to form a full outer shell, so that they may be stable and lead a happy atomic life.
Sometimes a DATIVE COVALENT bond forms. This happens when a molecule, once bonded, a lone pair of electrons and it chances to meet a +1 ion so the two react together to form positive ion with no more electrons to pair up.
LONE PAIR: Outer shell pair of electrons which are not involved in the chemical bonding.
DATIVE COVALENT BOND: A shared pair of electrons which has been donated by ONE of the bonding atoms.
Now we get onto the tough memorisation part: SHAPES! <---- Ugh the horror. Make sure you remember the examples AND the bonding angles AND the names.
The shape of the molecule is determined by repulsion between electron pairs surrounding the central atom.Lone pairs repel more than bonded pairs.
VERY IMPORTANT.
The type of bonding very much depends on something called the ELECTRONEGATIVITY.
ELECTRONEGATIVITY: It is the attraction of an atom on the bonded pair of electrons.
In short? The more electronegative an atom is the more it wants those electrons. So when you get two atoms which have a high difference in electronegativity, this results in a permanent dipole to form (one of the atoms becomes slightly positive and the other slightly negative). The resulting dipole results in a polar bond to form.
When the difference in electronegativity is very high then ionic bonding occurs where the atoms do not become slightly charged but have a full charge on them.
When there is no difference is electronegativity the reacting atoms form a covalent bond and share the electrons equally, they're not greedy.
However sometimes in a diatomic molecule (E.g. F-F or Cl-Cl) the electrons may be distributed unevenly. This results in an instantaneous dipole. This dipole will induce a dipole in the neighbouring molecule. The attraction between the instantaneous dipoles is Van der Waals's forces. The greater the number of electrons the greater the Van der Waal's forces.
This attraction is temporary and the electrons will move to another random place and create another instantaneous dipole in another direction.
There is another type of bonding that you need to know. It's called hydrogen bonding and yes it involves hydrogen.
HYDROGEN BONDING: A strong dipole-dipole attraction between an electron deficient atom and a lone pair on another molecule.
This type of bonding is strong (weaker than covalent but stronger than Van der Waals) and can only occur between molecules containing N-H and O-H.
This type of bonding give water very special properties:
- Ice is less dense tan water. Usually solid is more dense than liquid. However, in water (when freezing) more hydrogen form which hold then molecules apart. When ice melts again, the bonds break allowing the molecules to come closer together.
- Water has a relatively high melting/boiling point. This is because on top of Van der Waals there are also hydrogen bonds that need to be broken. Extra bonds - Extra energy.
- High surface tension and viscosity (thickness) of water. This all due to hydrogen bonds.
Final type of bonding is Metallic bonding.
METALLIC BONDING: The attraction of positive ions to the delocalised electrons.
Nothing to add there, very simple. All in the name: you have a metal that becomes +1 ion there will be one delocalised electron per each positive ion.
All the bonding is very important so make sure you memorise it as it needs to be applied to some higher end questions. Here is a quick summary:
- Ionic bonding
- Covalent bonding
- Dative covalent
- Electronegativity
- Permanent dipoles - Polar bonds
- Instantaneous dipoles - Van der Waals
- Hydrogen bonding
- Metallic bonding
There are many different structures (Eiffel tower and the pyramids being one of them):
Giant ionic lattices: These include ionic bonding which is very strong - E.g. NaCl (the common salt).
- High melting and boiling point - Strong forces means lots of energy.
- When solid the ions are fixed but when molten or in a solution the ions are free to move.
- Ionic lattices dissolve polar solvents, such as water. The lattice is broken down by the water molecules which surround each ion.
- High melting and boiling points - Strong covalent bonding.
- Non conductor of electricity as there are no free charged particles that can move.
- They are insoluble in both polar and non polar solvents, as the covalent bonds are too strong to be broken by solvents.
- High melting/boiling points - Strong metallic forces.
- Good conductors as delocalised electrons can move.
- Relatively high boiling point - Moderately strong hydrogen bonds.
- Low melting and boiling points - Weak Van der Waals's forces.
DIAMOND:
These shiny crystals are nothing more than carbon - literally. The carbon atoms are joined together by strong covalent bonds, which means a very high boiling/melting point.
They are rubbish at conducting electricity as there are no delocalised electrons and all outer electrons are used up in bonding. (I mean if you're running and juggling you can't be playing the piano at the same time, can you??)
On top of this they are very hard as the tetrahedral shape allows the applied force to be spread throughout the whole structure. (Another great example: when you're at a concert and you throw your self into the crowd - their hands will keep you from falling and they won't really feel your weight as it is spread out onto many people, easy eh??)
GRAPHITE:
Believe me or not this is diamond's sister (though not as shiny). It is also made of carbon alone. However graphite is made of strong covalently bonded layers, which is why you can draw with a pencil (the layers slide off).
It is a good conductor as there are delocalised electrons between the layers, which can move.
Unlike diamond, graphite is soft. This is because there are only weak Van der Waals's forces between the layers which allow them to slide off easily, even though the bonding within each layer is strong.
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