Halogens

The Halogens are 5 non metallic group 7 elements in the periodic table. They have slightly different properties because of their electronic setting (having 7 electrons in their outermost shells).

The most significant property of Halogens is their greatly high reactivity.

In terms of patterns and trends, as you move further down the group, electronegativity and reactivity decreases, while boiling points increase. (Exception of Astatine, because that stuff's radioactive).

Halogens have a high electronegativity, and are particularly reactive to form stable ionic crystals (Salts) as the name suggests, halo meaning salt and gen meaning to form.

**Sodium Chloride is the most abundant Halogen-produced Salt**

Sodium Chloride Crystals

The charge density of the nucleus of Halogens is important because it shows that they have a high proton charge, which grants them a good electronegativity making them ideal anions, for pairing with the 1st group cations such as Na+.

Halogens, as they have 7 electrons in their outer shells, have an oxidation number of -1, with a few exceptions, for example if it was binded with Oxygen or another Halogen that is more reactive, with Fluorine being the most reactive one.

The difference in reactivity between the group 7 elements is within the fact that they're in consecutive periods, meaning there's a hierarchy relating between the number of outermost shells and the reactivity of the element. This is relating to the idea that more rings around the nucleus make the outer-most shell further away from the centre point of electronegativity, so the pull is spread over a large area decreasing its concentration.

Halogens as oxidation agents follow this general form:

Electrophilic Addition

Electrophilic addition is basically this:

Like when you have a retarded bond that decides to jam itself into an unsaturated alkene. A bit like that relative you never liked. 

This happens in some stupid stages you're meant to remember. As if it'll mean anything to you in life.

Stage number one. The retarded bond ATTACKS the chilling alkene.

As the chilling alkene gets shanked by the retarded bond, one of its bonds snaps off. The electron's left hanging there.

As the bond's snapped off, the retarded bond makes advantage of this via exploiting the open port, as the following diagram illustrates.

And then we get this:

And then,

So, we end up with this:

Ionic Substances

Formed due to the loss or gain of electrons.

To make ions, an ionisation energy is required.

Ionisation energy is the amount of energy sufficient to remove an electron from the outermost shell of an atom.

The general equation for this is:

X _(g) à Na⁺ _(g) + _-1 e

When an outermost shell has been exhausted, and you start taken electrons off the next shell (Which would be full), the ionisation energy increases significantly.

I.e. All element is group one, have a large 2^nd ionisation energy. (Trying to remove the second electron)

Ions in solids

Ionic solids are giant lattices formed from ions being arranged in a regular way, and are held together by electrostatic bonds between oppositely charged ions.

This type of ionic bond is relatively strong and needs a large energy to overcome. For this reason, they have high melting and boiling points, so they tend to be solid at STP.

Ionic substances cannot conduct electricity when solid, but they can when in an aqueous solution.

The two ways of integrating H2O into an ionic substance:

1-      1- Water of crystallisation: Water sits in between ions of solids.

Example is Hydrated Copper Sulphate.

We include the water in the formulae. E.g. CuSO₄.₅H2O

2-      2- Hydration: Aka good old Dissolving.

Concentration Calculation

There are two methods to do concentration calculations, but to my concern as an Alevel chemist, only the following one is “Useful” because it includes Moles which can tell you a lot more about the substance and what its properties are as opposed to the singular sample you have in the experiment.

Concentration = Amount in moles ÷ Volume in cubic decimetres

1 decimetre cubed is equal to 1000 centimetres cubed!

Solutions in Geographical context

The following is mostly Geology and Biology and is of little interest to a real chemist.

The main two reasons behind the sea being salty are Hypothermal vents and Rain.

For some unmentioned reasons, chemistry A level students are required to recite the following:

The model for earth is that plate tectonics “float” on liquid mantle, and that they move due to currents caused by the constant change of mantle density resultant of nuclear shizzle radiating in the core.

So right, at the bottom of the ocean, those “trenches” allow the water to seep in. As the water seeps in, it flows against the molten mineral rocks, becoming a solution of those minerals and the water.

When the solution rises back to the ocean water, they cool down from the lethal 400 C’ to become black smokers ejecting sulphur and other minerals into the ocean, making a brilliant environment for bacteria to feed, colonise and grow.

The reason bacteria feed on this crap is because there’s no light for plants to photosynthesise at the bottom of the ocean so they have very different respiratory systems which were passed onto other life forms via evolution et cetera et cetera.

Then, as things are in the sea, big stuff eat smaller stuff. So the crabs would eat the bacteria for example.

Entropy

Not to be confused with Enthalpy.


Entropy is the degree of disorder.
Systems will move to a state of maximum disorder unless forced otherwise. (E.g. Tidying a room: If a room is not tidied periodically, it will eventually reach a state of optimum chaos)


exampli gratia, 
Diamond has a very ordered structure, so it's least disordered, so it has a low Entropy.

Gases don't have ordered structures, so they're most disordered, so they have a great Entropy.

Solids have the lower entropy.

Liquids have a medium entropy.

Gases have the greatest entropy.

Epsom Salts

Salts used by Victorians as a medical remedy. They're Magnesium Sulphates, made by bonding Magnesium Carbonate and Dilute Sulphuric Acid.

MgCO_{3 (s)} + H₂SO_{4 (aq)} --> MgSO_{4 (aq)} + CO_{2 (g)} + H₂O _(l)