AQA AS Chemistry Revision Notes 2: Periodicity & Mass Spectrometry

The following are the typical questions that you'll find in many of the past papers. Each question also comes along with the generic answer that the examiners are looking for, so if you learn these then you should be able to answer these questions pretty easily when they come up. If you think that I've missed out any important questions/answers or you'd like to correct any mistakes then feel free to mention them in the comments and I'll make adjustments as soon as possible.

Typical structure: Question (Marks Available) [Paper]: Answer. Extra notes/comments.

NB: Underlined words/phrases are the key terms needed to get the marks. Different points are highlighted in different colours.

AQA AS CHEMISTRY REVISION NOTES 2: PERIODICITY

Which atom in Period 2 (C to Fl) has the largest atomic radius, and why? (3) [May 2013]

Carbon. Has the lowest nuclear charge/weakest nuclear attraction to electrons, but has similar/same shielding.
 
Similarly,

Why does the atomic radius decrease as you go across the Period 2 elements? (2)

Nuclear charge increases/stronger attraction between the outer shell and nucleus; similar/same shielding.

The main points to remember are that the atomic radius decreases as you go from left to right, the nuclear charge always increases, causing the attraction between the nucleus and outer electron shell to increase, and the shielding (no of shells between the outer shell and nucleus) is similar/the same.

What's the general trend in first ionisation energies from carbon to neon? Which element deviates from this trend and why? (4) [May 2013]

Increase. Oxygen. Paired electrons. Paired electrons repel.

Not as complicated as it seems, eh? Just remember that from group 3 to 8/0, the ionisation energies increases as the nuclear charge increases, which means the outer electrons become more attracted to the nucleus. But at Group 6, the 4th electron in the p-orbital pairs with the 1st electron in said sub-shell, and as they're both negative, they repel each other, making it easier to ionise.

Why is the second ionisation energy of carbon higher than the first ionisation energy? (1)

More energy is required to remove the electron from the positive ion.

Remember, an electron has already been removed, meaning that there is now more protons than electrons, making it a positive ion.

Why does lithium have the highest second ionisation energy in Period 2? (1)

Electron removed from the 1p orbital.

The electron removed is closer to the nucleus, as it's in a different shell, so it requires more energy to remove.

Why is more energy required to remove an electron from Al³⁺ than an Na⁺ ion? (3)

More protons/stronger nuclear charge; Al³⁺ is smaller than Na⁺/electrons are close to the nucleus; electron gets more attraction/pulled more strongly by Al³⁺.


AQA AS CHEMISTRY REVISION NOTES 2.1: MASS SPECTROMETRY

How are the atoms ionised in a mass spectrometer? (2)

Electron gun fires high speed electrons; which knock off electrons from the gaseous atom.

How is current detected at the detector? (2)

Electrons are transferred from the detector to the (+) ion.

How is the relative abundance of an ion measured? (2)

Ions hit detector and accept electrons/cause an electron flow; a bigger current means more of that isotope/current is proportional to abundance.

Why do we only use the minimum amount of energy required to ionise the sample? (1)

So only one electron gets knocked out.

Whenever you talk about the atoms/substance/sample, remember that it's always been vapourised, and is therefore in a gaseous form, and never forget to put the state symbol when you're writing an equation eg. C_(g), Na_(g), O_(g) etc.


AKBIT-HOE, 23:45 15/05/2015

AQA AS Chemistry Revision Notes 1: Simple Definitions

The following are the typical questions that you'll find in many of the past papers. Each question also comes along with the generic answer that the examiners are looking for, so if you learn these definitions then you should be able to answer these questions pretty easily when they come up. If you think that I've missed out any important questions/answers or you'd like to correct any mistakes then feel free to mention them in the comments and I'll make adjustments as soon as possible.

Typical structure: Question (Marks Available): Answer.

NB: Underlined words/phrases are the key terms needed to get the marks. Different points are highlighted in different colours.

AQA AS CHEMISTRY REVISION NOTES 1: SIMPLE DEFINITIONS

Relative atomic mass (2):

(Average/mean mass of one atom of an element) ÷ (1/12 mass of one atom of ¹²C) OR

(Average/mean mass of atoms of an element) ÷ (1/12 mass of one atom of ¹²C) OR

(Average/mean mass of atoms of an element x12) ÷ (mass of one atom of ¹²C) OR

(Average mass of one mole of atoms) ÷ (mass of one atom of ¹²C) OR 

(Weighted average mass of all the isotopes) ÷ (mass of one atom of ¹²C) OR

Average mass of an atom/isotope (compared to C-12) on a scale in which C-12 has a mass of 12.

Mass number (of an isotope) (1):

Total number of protons and neutrons in the nucleus of an atom.

Electronegativity (2):

Power of an atom/nucleus to withdraw/attract electrons/electron density/a pair of electrons in a covalent bond.

Structural isomers (2):

Compounds that have the same molecular formula but a different structural/displayed/skeletal formula.

Rate of reaction (1):

Change in concentration (of a substance/reactant/product) in unit time/given time OR
Amount of substance used up/formed in unit time/given time.

Activation energy (1):

Minimum energy required for a reaction to start OR
Minimum energy for a successful/effective collision.


Le Chatelier's Principle (1):

If a factor is changed that affects an equilibrium, then the position of the equilibrium will shift/move so as to oppose/counteract the change OR
When a system/reaction in equilibrium is disturbed, the position of equilibrium shifts/moves in a direction which tends to reduce the disturbance.

What is a catalyst (1):

A substance that speeds up the reaction/alters the rate but is chemically unchanged at the end/not used up.

How does a catalyst work (2):

Catalyst provides an alternate route/pathway/different mechanism that has a lower activation energy.

Hess' Law (1):

The enthalpy change/heat (energy) change (at constant pressure) is independent of the route/path taken.

Carbon neutral (1):

An activity that has no net/overall carbon emissions to the atmosphere/air OR
An activity that has no net/overall greenhouse gas emissions to the atmosphere/air OR
There is no change in the total amount of carbon dioxide/carbon/greenhouse gases present in the atmosphere/air.

Mean bond enthalpy (2):

Enthalpy/heat (energy) change/required/needed to break/dissociate a covalent bond. Average/mean over different molecules/compounds/substances.

Hydration (1):

Addition of water to a molecule/compound.

Enthalpy change (1):

Heat energy change at constant pressure.

Standard enthalpy of combustion (3):

The enthalpy change when 1 mol of a compound/substance/alcohol is burned completely in oxygen OR is burned in an excess of oxygen with all reactants and products in their standard states OR with all reactants and products in their normal states under standard conditions.

Standard enthalpy of formation (3):

The enthalpy/heat change at constant pressure when 1 mol of a compound/substance/product is formed from its elements with all reactants and products in their standard states OR with all reactants and products in their normal states under standard conditions.

Empirical formula (1):

Lowest number/ratio of atoms of an element. 



I think this covers most of the simple definitions which you can easily learn to gain a few extra marks. Comment if there are any more that you think should be added to the list.


AKBIT-HOE, 22:47 15/05/2015

2015 Blog Update

Hey everyone, I just thought that I'd post a short update. I'd firstly like to say that I'm sorry that I haven't been posting anything in the past couple of months, as I wasn't expecting the leap from GCSE to AS to be as big as it turned out to be. Exams are coming up in less than a month, and they'll all be over in two. Hopefully I'll be able to get back into the whole blogging business again with posting random content that I feel would be good to write about.
I've had an idea in my mind from a while back, and honestly, I don't know whether this idea will be a success or whether I'll just end up making more work for myself. The idea was that I would write up revision notes and key ideas/structures that are useful (mainly AQA Biology and Chemistry) and I would post them onto here, so that I could share my revision with others who could probably look at them and gain one or two extra marks. I plan on trying this idea out to see how things go, and hopefully those of you who do the subjects that I do will find them as useful as I do.

I've also added a new subscription section to my blog, after a few requests from those of you who take your time to read my posts, which should be positioned to the right side of my blog. All you need to do is enter your e-mail and click the subscribe button, and the site will do the rest! What this will do I send you an e-mail every time I upload a new post, so that you'll get notified when it happens.
In other news, Tackling Racism Part 2 is still in progress; I'll hopefully be uploading it in the summer, along with a few other ideas that I'm brewing up in my head. This is all that I have to say, so good luck to everyone doing their exams this summer!

TL;DR Planning to upload stuff again in the summer. New idea where I post my revision notes for others to revise from. New subscription box.

AKBIT-HOE, 22:09 21/04/2015