Hot Trends

Periodic trends are trends across the periodic table. One of the ones you need to know is trends in melting point. i.e. how hot does it need to be to melt?

When you start to think about trends in melting points, you've got to think about what bond you need to break to melt it.

If you go through the options, it all becomes fairly self evident...

Let's look at Period 3 (Sodium to Argon)

and let's think about each element in turn and the bonds in the element. I repeat bonding in the ELEMENT. 

Why do I emphasise ELEMENT?

Ionic bonds occur between metals and non-metals. Never in elements. You need that difference in electronegativity for an ionic bond to occur. 

OK, let's look at the contenders for the highest melting point in period 3.

Sodium is a metal, so to melt it you have to break a metallic bond

Magnesium is a metal, so to melt it you have to break a metallic bond

Aluminium is a metal, so to melt it you have to break a metallic bond

Metallic bonds are strong and the trend is, the more electrons in the outer shell (i.e. donated to the sea of electrons) the stronger the metallic bond and the higher the melting point.

So of the three above Aluminium will be the highest (3 electrons donated to the sea), then Mg (2 electrons donated to the sea), then Sodium (1 electron donated to the sea).

Silicon is very similar to diamond in its structure it is a giant covalent compound. Covalent bonds are very strong. Even stronger than metallic bonds so the MP will be higher again than aluminium

Phosphorus, Sulfur, Chlorine are all simple covalent compounds. That is little covalent molecules (P4, Cl2, S8) each compound has covalent bonds in the molecule but these don't break when you melt it so they don't matter. What matters is they have Van der Waals between the molecules and these are very weak. So the melting points are all very low.

Argon is a similar story to P, S and Cl but they don't even have the covalent they are just individual atoms joined by Van Der Waals forces so again very low melting points.

All in all, Silicon has the highest melting point because you have to break the strongest bond (covalent) to melt it.

Cheshire, Felix, Garfield, Tom, Pilchard, Scratchy, Stimpy, Sylvester, Snowball

What do this bunch have in common?

Do they speed up reaction? Nope
Do they manage to not get used up in reactions? Probably not
Do they allow alternative pathways? Nope
Are they unchanged during a reaction? Nope
Do they change the position of an equilibirum? erm, well, no, probably not

because they are a "list-of-cats" and not "catalysts"

(Apologies, possibly worst intro ever, let's move on)

Catalysts (unlike lists of cats) are useful industrially for a number of reasons. New catalyst development is part of what is called green chemistry. Let's run through the uses of catalysts one by one...

1. Allow usage of lower temperatures
2. Allow usage of lower pressures

If somebody asked you the question - What does Airbus make? I am sure you would say the answer aeroplanes, but you would be wrong, Airbus make money, aeroplanes are merely the medium they use. So, for any manufacturing company, cost saving is important and by reducing the temperature and pressure required in their factories they lower energy costs.

Additionally, reducing energy usage reduces greenhouse emission in power plants (less energy = less CO2 made.

Finally, lowering pressure makes your factory safer to operate. You don't want to be around when a high pressure vessel (whale based or otherwise) explodes. 

3. New production routes and products become possible

Put simply new catalysts = new chemicals and new ways of making chemicals. Why this is important will vary from scenario to scenario, it could be cheaper, it could involved less toxic reactants or by products, it could be a new chemical that is better at its intended job etc.

Anybody not feeling sick having watched that whale explode a dozen times. Try this fact.

Beached whales tend to explode due to a build up of a combination of methane, hydrogen sulphide and ammonia. So it effectively smells of farts, stink bombs and urine.

No wonder the tango man runs.

IT'S A BOMB!!!!!!

Ever wondered what exactly a bomb calorimeter is? Well, this is a bomb calorimeter.

It is basically a really, really, really well insulated container full of water that contains another container inside it that can burn any chemical to completion without losing any heat (well, very, very, very little heat).

Not impressed? Thought it would be a bit more James Bond? 'Fraid it is more Borne-Haber than Bourne Identity (Google it)

What is the point of it?
By using a Bomb Calorimeter, you can very accurately measure the enthalpy of combustion because no heat is lost to the environment, it is all used to raise the temperature of the water.

What do you need to know about it for CH1?
Very little, only that it is an improvement over using a polystyrene coffee cup and a plastic lid with a thermometer pushed through it

Hold on, just had a thought, if you used a bomb calorimeter to keep your coffee in, it would stay hot forever! Why hasn't somebody else thought of this? Infinity Coffee! It could be a big seller, you heard it here first.

What's HOT and What's NOT in the world of Chemistry (or Spot the Difference)

Whenever they change specification (like they did 4 years ago) they always take some stuff out and put other new stuff in. 

There is no good reason why, except to confuse pupils and teachers . So, those of you doing the old specification papers will be very confused from time to time when they ask a question that looks like it is written in greek because you don't recognise the stuff at all or you didn't think you needed to know in that level of detail.
So, to help you through, here is a list of all the changes that come to mind. I may have missed something, so please point in out if there is something else that you think is different.

AS
New In!
Hydrogen Emmission Spectrum
Smart Materials
Carbon Nanotubes
Nanotechnology
Green Chemistry

Gone!
Electron Density Distribution

Equilibrium Constants (now in A2)

A2 

New In!

Hydrogen Fuel Cell

Group 3

Chromatography

Gone!

Group 1 and 2

Hydrogen Emission Spectrum (now in AS)