TOPIC 1 - ATOMIC STRUCTURE AND THE PERIODIC TABLE Flashcards
What is covalent bonding?
Each atom shares an electron with another atom.
What is ionic bonding?
Ions are strongly attached to each other. Opposite charges.
What is the symbol for sodium chloride?
NaCl
What is the symbol for hydrochloric acid?
HCl
What is the symbol for sulphuric acid?
H2SO4
How do you do paper chromatography?
Draw a line near the bottom of a sheet of filter paper (use a pencil)
Add a spot of ink to the line and place the sheet in a beaker of solvent eg water
Make sure the ink isn’t touching the solvent
Place a lid on top to prevent evaporation
Each different dye will move up the paper at a different Faye so the dyes will separate out. Each dye will form a spot in a different place.
The end result is a pattern of spots called a chromatogram.
What is filtration used for?
To separate insoluble solids from liquids.
Filter paper is folded into a cone shape - the solid is left in the filter paper.
What methods can be used to separate soluble solids from liquids?
Evaporation
Crystallisation
What is evaporation?
Pour the solution into an evaporating dish.
Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated. Eventually, crystals will start to form. Keep heating the evaporating dish until all you have left are dry crystals.
(Can only be used if the salt doesn’t decompose when heated - otherwise you have to use crystallisation)
What is crystallisation?
Pour the solution into an evaporating dish and gently heat the solution. Some of the solvent will evaporate and the solution will get more concentrated.
Once some of the solvent has evaporated, or when you see crystals start to form (the point of crystallisation), remove the dish from the heat and leave the solution to cool.
The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution.
Filter the crystals out of the solution, and leave them in a warm place to dry. You could use a drying oven or a desiccator.
How can you separate rock salt?
Filtration and crystallisation
Grind the mixture to make sure the salt crystals are small, so will dissolve easily. Put the mixture in water and stir. The salt will dissolve, but the sand won’t. Filter the mixture - the grains of sand won’t fit through the tiny holes in the filter paper, so they collect on the paper instead. The salt passes through the filter paper as its part of the solution. Evaporate the water from the salt so that it forms dry crystals.
What is distillation?
Used to separate mixtures which contain liquids.
What is simple distillation?
Used for separating out a liquid from a solution. The solution is heated. The part of the solution that has the lowest boiling point evaporates first. The vapour is then cooled, condenses (turns back into a liquid) and is collected.
The rest of the solution is left behind in the flask. This can be used to get pure water from sea water.
The problem is that it can only be used if there are very different boiling points. Fractional distillation can be used if the boiling points are similar.
What is fractional distillation?
You put the mixture in a flask and stick a fractionating column on top. Then you heat it. The different liquids all have different boiling points - so they evaporate at different temperates. the liquid with the lowest boiling point evaporates first. When the temperature on the thermometer matches the boiling point of the liquid, it will reach the top of the column. Liquids with high boiling points might also start to evaporate. But the column is cooler at the top so will only get part of the way up before condensing and running back down towards the flask. When the first liquid has been collected, you raise the temperature until the next one reaches the top.
What did JJ Thompson say about the atom?
‘Plum pudding model’ containing negatively charged electrons.
What did Rutherford say about the plum pudding model?
Conducted the alpha particle scattering experiment. They fired positively charged alpha particles at an extremely thin sheet of gold. Because the the previous plum pudding model they expected the particles to pass star ugh the through or be slightly deflected at most. This is because the positive charge of each atom was thought to be very spread out. However, while some particles did go straight through, some were deflected more than expected. Some were even deflected straight backwards. This proves that the plum pudding model couldn’t be right. He came up with the NUCLEAR MODEL. In this there is a tiny positively charged nucleus at the centre of the atom, where most of the mass is concentrated. A ‘cloud’ of negatively charged electrons surround this nucleus. So most of the atom is empty space. When the alpha particles came near the concentrated positive charge of the nuclear they were deflected. If they were fired directly at the nucleus they were deflected backwards. Otherwise, they passed through the empty space.
What was Bohr’s nuclear model?
Suggested that all the electrons were contained in shells. He proposed that electrons orbit the nucleus in fixed shells and aren’t anywhere in between. Each shell is a fixed distance from the nucleus.
What further experiments show the existence of electrons?
Rutherford showed that the nucleus can be divided into smaller particles, which each have the same charge as a hydrogen nucleus. These particles were named protons.
James Chadwick carries out an experiment which provided evidence for neutral particles in the nucleus which are now called neutrons.
