Atomic Structure

Atom

Smallest part of an element

Compounds

Two or more different elements chemically bonded together.

Mixture

Consists of two or more elements or compounds that are not bonded together.

Are the chemical properties of each substance in the mixture changed?

No, they are unchanged

Mixtures can be separated by physical processes such as: 5

filtration

crystallisation

simple distillation

fractional distillation

chromatography

These physical processes do not involve chemical reactions and no new substances are made.

pure

a substance that consists of only one element or compound

what is filtration used for?

give an example

used to separate an insoluble solid from a liquid.

e.g. separating sand and water or excess reactant from a reaction mixture.

give the method for filtration (3) + draw diagram

1. Set up apparatus as shown

2. Pour the solid and liquid mixture into the filter funnel

3. the liquid drips through the filter paper but the solid particles are caught in the filter paper.

What is crystallisation used for?

give example

Used to produce solid crystals from a solution.

e.g. obtain copper sulfate crystals from copper sulfate solution.

give the method for crystalisation(2) + draw diagram

1. Place the solution in an evaporating basin and gently heat it with a Bunsen burner.

2. remove the heat when insoluble crystals start to form.

what is simple distillation used for?

give an example

Used to separate solvent from a solution.

e.g. pure water from seawater

method and diagram for simple distillation

1. Salty water is heated

2. the water vapour cools in the condenser and drips into a beaker

3. The water has condensed and is now in the beaker, the salt stays behind

What is fractional distillation used for?

give example

Used to separate different liquids from a mixture of liquids.

e.g. separating different fractions from crude oil

method for fractional distillation + draw labelled diagram

1. Vapours rise through a column which is hot at the bottom, and cooler at the top.

2. Vapours condense when they reach a part of the column that is below the temperature of their boiling point.

3. each liquid is led away from their column

Write the chronological order of the discoveries of the model of atoms over time.

1. Dalton - tiny indivisible spheres

2. Discovery of the electron led to the plum pudding model of the atom - ball of positive charge with electrons in it - JJ - Thompson.

3. Results from the gold foil experiment led to the conclusion that mass of an atom was concentrated in the centre and that it was positively charged. - Geiger, Marsden, Rutherford

4. Niels Bohr then adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.

5. Later experiments led to the idea that the positive charge of the nucleus could be subdivided into smaller particles, called the proton.

6. James Chadwick provided evidence to show the existence of neutrons within the nucleus, 20 years after the nucleus became an accepted scientific idea.

radius of an atom

0.1nm (1 ×10^-10m)

radius of the nucleus

less than 1/10,000 of the atom itself (about 1×10^-14m)

relative atomic mass

The average mass of the isotopes of the atom relative to 1/12 of the mass of a carbon-12 atom

relative isotopic mass

mass of an isotope relative to 1/12 of the mass of a carbon-12 atom.

relative molecular mass

The average mass of a molecule relative to 1/12 of a carbon-12 atom.

List the name of the processes in the Mass Spectrometer

1. Ionisation

2. Acceleration

3. Ion Drift

4. Detection

Describe the two ways to ionise substances before they go in the mass spectrometer

1. Electrospray Ionisation - The sample is dissolved in a solvent and pushed through a small nozzle at high pressure. A high voltage is applied to it, causing each particle to gain a H+ ion. The solvent is removed, leaving a gas of positive ions.

2. Electron impact ionisation - The same is vapourised and an ‘electron gun’ is used to fire high energy electrons at it. This knocks one electron off each particle so they become +1 ions.

Explain what happens in stages Acceleration and Ion drift.

The positive ions are accelerated by an electric field. All ions have the same kinetic energy. Lighter ions accelerate more.

How does the ion detector use the data to calculate the mass/charge values needed to produce a mass spectrum

• it detects the current created when the ions hit it

• records how long they took to pass through the spectrometer.

How to calculate the relative atomic mass using mass spectra

• Y-axis shows the percentage abundance of each isotope

• X-axis shows the mass number of each isotope

• Use these values to calculate the relative atomic mass in the usual way.

mass/ charge ratio

mass number of an atom/ molecule

3 rules for electron configurations

1. Electrons fill up the lowest sub-shells first. (4s is below 3d and so it fills up first.)

2. Electrons fill up orbitals in a sub-shell singly before they start sharing.

3. For the configurations of ions, just add or remove electrons from the highest energy occupied sub-shell.

Factors effecting ionisation energy

Nuclear charge

Shielding

Distance from the nucleus

Define first ionisation energy

The first ionisation energy is the energy required to remove 1 electron atom each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Draw the graph of the ionisation trend of period 3

Explain the dip at group 3

• Aluminium’s outer electron is in a 3p orbital rather than a 3s. 3p orbitals have slightly more energy than the 3s orbital, so the electron is, on average, to be found further from the nucleus.

• The 3p orbital has additional shielding provided by the 3s electrons

These two factors together are strong enough to override the effect of the increased nuclear charge, resulting in the ionisation energy dropping slightly.

Explain the dip at 6

electron pair repulsion