C1- Atomic structure ⚛️

All the elements.

• an element, is a substance made of one type of atom [because each atom of an element, has the same number of protons]

• A compound is two or more elements that are chemically combined, in a fixed proportion.

• A mixture is different element or compounds, that aren’t chemically combined (together).

• A molecule has any elements chemically joined (they can be the same element).

• An atom is the smallest part of an element, that can exist.

• Count the big numbers for elements . E.g= MgS, has two elements: magnesium + sulfur. • If there’s a number next to them, thats how many atoms there are. In MgS, there would be one atom of magnesium + one atom of sulfur.

• filtration • crystallisation • distillation • chromatography

• We can use physical separation techniques, to separate mixtures. For example- filtration

• Filtration is used to separate an insoluble solid from a liquid.

• use a filter funnel + filter paper • pour the mixture into filter paper + the liquid passes through tiny pores in the filter paper • so the solid can’t pass through the filter paper, so it’s trapped.

• pour solution into an evaporating dish + gently heat the solution. • some of the solvent will evaporate + the solution will become more concentrated. • When the solvent evaporates/when crystals start to form, remove the dish from the heat + leave solution to cool. • salt should start to form crystals, as it becomes insoluble in the (cold + highly concentrated solution). • Then filter the crystals from the solution, leaving them in a warm place to dry.

• Simple distillation is used, to seperate a liquid from a solid, if we want to keep the liquid.

• Fractional distillation allows us to separate two different liquids. [that have different boiling points]

• First place the solution with the liquid and dissolved solid in a flask, with is connected to a continuous glass tube. • the glass tube is surrounded by a condenser, and cold water from the tap, continuously runs through the condenser- keeping the internal glass tube cold. • After running the condenser, the water then goes down the sink.

• the solution is first heated + the part of the solution with the lowest boiling point, evaporates first. • the vapour is then cooled, condenses [back into a liquid] and is collected. • ; the rest of the solution is left behind in the flask. • [ ; simple distillation is carried out: by evaporating the liquid (by heating), then condensing the vapour (by cooling)]

• put the mixture in a flask + add a fractionating column on the top. Then begin to gently heat. • since the different liquids will have different boiling points, they will evaporate at different temperatures. • the liquid with the lowest boiling point evaporates first + when the temperature on the thermometer reaches the boiling point of the liquid, it then reaches the top of the column. • ; liquids that have higher boiling points might begin to evaporate- but they will condense and run back towards the flask [as the fractionating column is cooler, towards the top] • Finally, when first liquid is collected, raise the temperature again [until the next liquid/chemical reaches the top]

• The experimental results of the gold foil experiment could not be explained using the plum pudding model. • so the plum pudding model was disapproved and a, new model called the nuclear model (Bohr) was made to match the results.

Nuclear model of atom: • The atom is mostly empty space + negative electrons orbit the nucleus at a distance • almost all the mass of an atom was actually concentrated in the positively charged nuclues. Plum pudding model: • the atom is a positively charged ‘ball’ of positive charge • mass of atom is evenly distributed. • negative electrons are distributed through the atom.

• Some of the alpha particles were deflected= so the centre must have a positive charge + that repelled alpha particles.

• most of the alpha particles went straight through the gold foil = so therefore atoms are mainly empty space. [meaning the plum pudding model had to be wrong]

• Some alpha particles bounced straight back= so the mass of an atom, must be concentrated in the centre/the nucleus • [nuclear model replaced plum pudding model]

• the ancient greeks thought, that everything is made of atoms + atoms are tiny spheres, which can’t be divided.

• Rutherford took a piece of gold foil [gold can be hammered into a few atoms thick] • and he and his scientists, fired alpha particles from a helium nuclei.