Topic 1 - Atomic Structure And Periodic Table Flashcards
Masses of particles
Protons: 1
Neutron: 1
Electron: very small
Charge of particles
Proton: +1
Neutron: 0
Electron: -1
Why atoms are neutral
Have no charge overall as number of protons is the same as electrons (unlike ions)
Isotope definition
Different forms of the same element which have the same number of protons but a different number of neutron
Giving them the same atomic number but different mass
Formula of relative atomic mass of an element
RAM= sum of (isotope abundance x isotope mass number/ sum of abundances of all the isotopes)
What is a compound
Substances formed from two or more elements
Held together by chemical bonds
Making bonds involved atoms taking or giving electrons - only electrons involved
It’s usually difficult to separate the original elements of a compound out again - chemical reaction is needed
Why are mixtures easily separated
There is no chemical bond between the different parts of the mixture
Method of chromatography
1) draw line near bottom of filter paper(in pencil as it is insoluble)
2) add a spot of ink to the line and place sheet in beaker of solvent
3) solvent used depends on what’s being tested.
4) make sure ink isn’t touching solvent as it may dissolve into it
5) place kid on top of container to stop solvent evaporating
6) solvent seeps up paper carrying the ink with it
7) each different dye in the ink will move up the paper at a different rate so the dyes will separate out. Each due will form a spot in a different place
8) if any of the dyes are insoluble they will stay on the baseline
9) when the solvent has nearly reached the top of the paper take it out the beaker and leave to dry
10) end result is a chromatogram
Two ways to separate soluble solids from solutions
Evaporation
Crystallisation
Evaporation method
1) pour solution into evaporating dish
2) slowly heat the solution. Solvent will evaporate and solution will get more concentrated. Eventually, crystals will start to form
3) keep hearing the evaporating dish until all you have left is dry crystals
Crystallisation
1) pour solution into evaporating dish and entry heat the solution. Some solvent will evaporate and the solution will get more concentrated
2) once some solvent has evaporated or when crystals start to form, remove the dish from heat and leave solution to cool
3) the salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
4) filter the crystals out of the solution and leave in a warm place to dry
Simple distillation method : used to separate solutions
1) solution is heated . Part of solution with lowest boiling point evaporates first
2) vapour is then cooled, condensed and is collected
3) Rest of solution is left behind in flask
Problems with simple distillation
Can only be used to separate things with very different boiling points - if temp goes higher than boiling point of the substance with the higher boiling point they will mix again
Fractional distillation method : used to separate mixture of liquids
1) put mixture in flask and put fractionating column on top, then heat
2) different liquids will all have different boiling points so will evaporate at diff. temperatures
3) liquid with lowest boiling point evaporated first. When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column
4) liquids with higher boiling points might also start to evaporate , but the column is cooler towards the top. So they will only get part of the way up before condensing and running back down towards the flask
5) when the first liquid has been collected, raise the temperature until the next one reaches the top
Development of the atomic structure
1) start of 19th century John Dalton described the atoms as solid spheres and that different spheres made up different elements
2) 1897- JJ Thompson concluded atoms weren’t solid spheres. His measurements of charge and mass showed the atom must contain even smaller, negatively charged particles called electrons
3) this new theory was called the ‘plum pudding model’ and it showed the atom was a ball of positivel charge with electrons stuck in
How Rutherford showed the plum pudding model was wrong
In 1909 Rutherford conducted the famous ‘alpha particle scattering experiments’ where they fired positively charged alpha particles at an extremely thin sheet of gold
From the plum pudding model they expected the particles to pass straight through or be slightly deflected at most as the positive charge of each atom was thought to be very spread out within the atom. Although most particles did pass straight through , some were deflected more than expected.
Rutherford came up with the hypothesis that there is a tiny positively charged nucleus at the centre where most mass is concentrates and a cloud of negative electrons surrounded the nucleus so most of the atom is empty space
Why Dmitri left gaps in the early periodic table
To make sure elements with similar properties stayed in the same groups. Some of the gaps indicated the existence of undiscovered elements and allowed Mendeleev to predict what their properties might be
In the modern periodic table what forms columns
Elements with similar properties
These vertical columns are called groups
What does the group number tell in the modern periodic table
How many electrons are in the outer shell
This means all elements in the same group will react similarly
Reactivity in group 1
Elements react more vigorously as you go down the group
Reactivity in group 7
Reactivity decreases as you go down the group
What are the rows in the modern periodic table
Periods
Each new period represented another full shell of electrons
Metal physical properties
- strong but malleable
- great at conducting heat and electricity
- have high bp and mp
Non metal physical properties
- more brittle as they aren’t always solids
- don’t generally conduct electricity
- lower density
