Fractional distilation

• Fractional distilation seperates a mixture into a number of different parts called fractions
• A tall collum if fitted above the mixture differetn pipes coming off it
• The collum is HOT at the bottom and COLD at the top.
• Subsances with HIGH high boiling points condense at the bottom, and substances with LOW boiling points condense near the top. Gases esacpe from the very top
• The substances in crude oil condense at different temperatures and can be seperates out with this method
• The gases are realsed at the top of the collum but the liquids are realsed in the middle of the collum and the solids from the bottom

Chromatography

The colours separate and move up the paper at different rates

Chromatography can be used to separate mixtures of coloured compounds. Mixtures that are suitable for separation by chromatography include inks, dyes and colouring agents in food.

Simple chromatography is carried out on paper. A spot of the mixture is placed near the bottom of a piece of chromatography paper and the paper is then placed upright in a suitable solvent, eg water. As the solvent soaks up the paper, it carries the mixtures with it. Different components of the mixture will move at different rates. This separates the mixture out.

Rf values

Different chromatograms and the separated components of the mixtures can be identified by calculating the Rf value using the equation:

Rf = distance moved by the compound ÷ distance moved by the solvent

The Rf value of a particular compound is always the same - if the chromatography has been carried out in the same way. This allows industry to use chromatography to identify compounds in mixtures.

The History of The Atom

The theory of the atomic structure:

• 1) At the beginning of the 19th century, John Dalton described atoms as solid spheres, and different spheres made up different elements. 
• 2) In 1897, J J Thompson found out that atoms weren't solid spheres and showed that an atom must contain even smaller, negatively charged particles- electrons.
  • This became known as the 'plum pudding model' which showed the atom as a ball of positive charge with electrons stuck in it.

The alpha particle scattering experiment:

• In 1909, Ernest Rutherford conducted an experiment by which he fired positively charged alpha particles at an extremely thin sheet of gold.
• Most of the particles passed straight through the gold sheet, however some particles were deflected more than expected and a small number deflected backwards.
• Rutherford came up with the 'nuclear model' of the atom. In this, there's a tiny positively charged nucleus at the centre, surrounded by a 'cloud' of negative electrons -------------->

The alpha particle scattering experiment (continued):

• Most of the atom was empty space. 
• When alpha particles came near the positive charge of the nucleus, they were deflected. If they were fired directly at the nucleus, they would deflect backwards, otherwise they would just pass through empty space.

Bohr's nuclear model:

• 1) Scientists realised that electrons surrounding the nucleus would be attracted to the nuceus, therefore causing the atom to collapse.
• 2) Niels Bohr's nuclear model of the atom suggested that electrons were contained in shells.
• 3) Bohr said that electrons orbit around the nucleus in fixed shells and each shell is a fixed distance from the nucleus.

The existence of protons:

• 1) Rutherford and others came to a conclusion that the nuceus could be divided into smaller particles, each of which has the same charge as a hydrogen nucleus.
• 2) James Chadwick, 20 years later, carried out an experiment which proved there were neutral particles in the nucleus- neutrons. 

Electronic structure:

1st shell: 2   2nd shell: 8   3rd shell: 8

The Sub-Atomic Particles

Protons:

Have a relative charge of + 1

Have a relative mass of 1

Neutrons:

Have a relative charge of 0

Have a relative mass of 1

Electrons:

Have a relative charge of -1

Have a relative mass so small that it would take almost 2000 electrons to make the same weight as a proton.

Atomic Number

All atoms of a particular element have a particular number of protons.

The number of protons in each atom of an element is called the atomic number.

The elements of the periodic table are arranged in order of their atomic number.

Mass Number

The number of prottons plus the number of neutrons in the nucleus of an atom is the mass number.

Number of neutrons = Mass Number - Atomic Number.

What is an ion?

Sometimes, when an atom gains one or more electrons, e.g when a metal reacts with a non-metal, then it gains a negative charge because it has more electrons than protons, which means more negativity than positivity. You would say it has become a negative ion.

When it loses electrons, it would be a positive ion because it has more protons than electrons.

An ion is a charged atom.

Representing Mass and Atomic Number.

The bottom number is the its atomic number giving you the protons.

The top number is the mass number.

The Size of Atoms.

At least 7 billion billion billion atoms in the human body:

7000000000000000000000000000

Isotopes.

Atoms of the same element always have the same number of protons, however there can be different numbers of neurons.

Atoms of the same element which have different numbers of neutrons are called isotopes.

Sometimes extra neutrons make the nucleus unstable, so it is radioactive. 

However, most are simlply atoms of the same elements that has a different mass.

Samples of isotopes of an element have different physical properties.E.g different density, they may or may not be radioactive.

Electronic structure

The electronic structure of an atom is a description of how the electrons are arranged. It can be shown as numbers or as a diagram.

Electron configuration diagram for lithium

Take lithium for example. The diagram shows each energy shell as a circle around the nucleus, with each electron represented by a dot. In the exam, do not worry about colouring in the electrons. Just make them clear and ensure they are in the right place. Sometimes you will be asked to use a cross rather than a dot.

The electronic configuration for lithium is written as 2.1 (showing that lithium atoms have three electrons, two in the first shell and one in the second shell).

The table describes the electronic structures of four more elements.

Electronic structures of elements

ElementNumeric formatElectronsPeriodic table group

F 2.7 Fluorine atoms have nine electrons. Two of these fit into the first energy shell. The remaining seven fit into the second energy shell. Group 7

  Ne 2.8 Neon atoms have ten electrons. Two of these fit into the first energy shell. The remaining eight electrons fit into the second energy shell. Because its highest occupied energy shell is full, neon is stableand unreactive. Group 0 - that is, the eighth group

Na 2.8.1 Sodium atoms have 11 electrons. Two of these fit into the first energy shell, eight into the second energy shell. The last one fits into the third energy shell. Group 1

Ca 2.8.8.2 Calcium atoms have 20 electrons. Two of these fit into the first energy shell, eight into the second energy shell, another eight into the third energy shell. The last two fit into the fourth energy shell. Group 2