Wednesday, 13 February 2013

1.15 deduce the number of outer electrons in a main group element from its position in the Periodic Table.

The groups (that's going down the periodic table) tell you how many electrons are on the outer shell!

Also note that the periods (going across) tell you the number of orbitals the atom has.

1.14 deduce the electronic configurations of the first 20 elements from their positions in the Periodic Table

Groups are colmns in the periodic table; the group number represents the number of electrons on the outer shell.

Periods are rows on the periodic table; the row corresponds with number of shell.

So if you have an element on the third row down in group seven: it will have three shell and 7 electrons on its outer shell.

1.13 understand that the Periodic Table is an arrangement of elements in order of atomic number

As you can see above the periodic table is in order of atomic number.
Every atom in an element has the same atomic number.

1.12 calculate the relative atomic mass of an element from the relative abundances of its isotopes

Relative atomic mass is the average weight of an atom of an element. There is variation in the weight due to the fact that there are different isotopes with in an element. (Different isotopes have different weights due to less or more neutrons.)

It is calculated like this:
(% of isotope x its mass) + (% of isotope x its mass) / 100

e.g for chlorine
75% of all chlorine has a mass of 35. 25% of all chlorine has a mass of 37.
(75 × 35) + (25 × 37)100
2625 + 925100
= 35.5

1.11 understand the terms atomic number, mass number, isotopes and relative atomic mass (Ar)

Atomic number: number of protons (the same as number of electrons.)

Mass number: number of protons + neutrons.

Isotopes: Atoms of an element with different numbers of neutrons.

Relative atomic mass (Ar): the mass of one atom of an element.

1.10 recall the relative mass and relative charge of a proton, neutron and electron

Relative charge
Proton: +1
Neutron: No charge
Electron: -1

Relative mass

Proton: 1
Neutron: 1
Electron: Nearly nothing

1.9 understand that atoms consist of a central nucleus, composed of protons and neutrons, surrounded by electrons, orbiting in shells

The protons and neutrons in the centre make up the nucleus
The electrons are orbiting on shells (or orbitals)

1.8 explain how information from chromatograms can be used to identify the composition of a mixture.

Chromatography paper is placed in a solvent, the different compounds will travel at different speeds (due to the size of their particles.)

Rf values
The Rf value is calculate by Distance moved by compound divided by Distance moved by solvent.

The shape on the chromatogram can be compared with that of known substances and where they match they are the same substance.

1.7 describe experimental techniques for the separation of mixtures, including simple distillation, fracti onal distillation, filtration, crystallisation and paper chromatography

This consists of a barrier which one component f a mixture can pass through but the other is caught by.
e.g water goes through filter paper, rocks are caught by it.

One substance is evaporated off.
e.g salt water is heated to 100 degrees; water evaporates off (it rises and the goes down into the condenser where it is cooled back into water), the salt is left in the original flask. See diagram.

Fractional distillation
The mixture is evaporated and rises up the tube.
Different substances have different boiling points and so will condense at different temperatures; as the mixture travels up the tube the temperature decreases, substances begin to condense at different places (due to the change in temperature) and are collected. This separates the mixture into its different parts.

A solution is warmed allowing the solvent to evaporate, the solution is now left to cool and will form crystals.

chromatography paper is placed in a substance, the different components of the substance will travel at different speeds (due to the size of their particles.)

1.6 understand the differences between elements, compounds and mixtures

Elements- every atom in an element has the same amount of protons.

Compound- atoms from different elements bonded together

Mixture- different elements not bonded.

1.5 understand the terms atom and molecule

An atom is made up of a nucleus (protons and neutrons) and orbitals with electrons on:

A molecule is two or more atoms bonded together.

1.4 describe and explain experiments to investigate the small size of particles and their movement including: i dilution of coloured solutions ii diffusion experiments

Dilution: a substance is put in a solvent to reduce its concentration
Diffusion: The movement of particles from an area of high concentration to an area of low concentration

Experiment 1, Diffusion
Hydrochloric acid is placed at one end of a tube, ammonia solution at the other.
Where they meet a ring of ammonium chloride appears.
The diagram shows it is closer to the HCL end.
From this we can tell that ammonia must have travelled faster, as it got further in the time. Lighter particles travel faster- so we can tell that ammonia is a lighter gas.

Experiment 2, Dilution
Put a coloured substance in a solvent e.g food colouring in water.
You can see that over time the colour levels out but is weaker than the original colour- this is dilution.
Dilution at different temperatures: more heat; means more energy; means more movement; so the particles can move to different areas more quickly. So applying heat decreases the amount of time taken for the coloured substance to be fully diluted.

1.3 explain the changes in arrangement, movement and energy of particles during these interconversions.

Solid: still; no energy; all particles touching

Add heat v / Remove heat ^

Liquid: Moving to fit space; some energy; all particles touching

Add heat v / Remove heat ^

Gas: Moving freely; lots of energy; particles not touching.

1.2 understand how the interconversions of solids, liquids and gases are achieved and recall the names used for these interconversions

Solid > Liquid
This process is called melting: you apply heat.

Liquid > Solid
This is freezing. You remove heat.

Liquid > Gas
Heat is added. The process is evaporation.

Gas > Liquid
Removed heat: condensing.

Diagrams are helpful to understand this concept. Be aware that you don't need to know the process between solid and gas/ gas and solid.

1.1 understand the arrangement, movement and energy of the particles in each of the three states of matter: solid, liquid and gas

As the picture shows, all the particles in a solid are touching. Another feature of a solid is that the particles aren't moving, the particles have no energy.

Liquid particles are, like solids, all touching. The difference is that liquid particles are moving- they flow to fit the space- this means that they have some energy.

In gasses the particles aren't all touching; they are far apart. They move freely and have a high energy level.