Introduction to the periodic table and the structure of the atom Flashcards
What is an Element?
In an Element all of the atoms are the same.
What is a compound?
- Two or more different elements chemically combined in a fixed proportion.
- ## Has different properties compared to the elements they are made from.
How do we separate a compound back into it’s elements?
- We need to use a chemical reaction.
- However, this may be difficult to do.
What is a mixture?
- Different elements or compounds not chemically combined together.
- To seperate a mixture we need to use a physical method rather than chemical approach.
What is a molecule?
- Has any element chemically joined.
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What is a chemical formula?
- Tells us the elements in a molecule and the number of atoms for each elements. E.g: MgS. This shows 1 atom of Magnesium. 1 atom of sulphur. Example 2: Na>2SO>4 2 sodium atoms, One sulphur atom. 4 oxygen atoms.
- In a specific compound the number of atoms of each element is fixed.
“Filtration and Crystallisation”
- This is a physical separation techniques.
- Used to separate mixtures.
- Cannot be used to separate a compound.
What is filtration?
- Separate an insoluble solid from a liquid.
Method: - Use a filter funnel and a filter paper.
- Pour the mixture into the filter paper.
- The mixture passes through.
- The solid cannot pass through the filter paper so is trapped.
- The liquid and solid is now seperated.
What is crystallisation?
- Used to separate a soluble solid from a liquid.
- Aqueous solution: Solid dissolved in a liquid.
- The solution in a beaker.
1) Leave for a couple of days and let the water to dissolve.
2) Gently heat the solution using a Bunsen burner and be careful that heating does not affect the chemical trying to crystallise
E.g: Certain chemicals break down if we try to heat them so its best to leave the water to evaporate on its own.
What is simple distillation?
- Separate the liquid from a solid if we want to keep the liquid.
- Evaporate the liquid by heating.
- Condense the vapour by cooling.
Equipment:
- Flask: We place the liquid and the dissolved solution in a flask.
- The flask is connected to a continuous glass tube.
- Condenser: Cold water runs through the condenser continuously to keep the internal glass tube cold.
- Theremoter.
Method:
1) Heat up the solution with a Bunsen Burner.
2)Heating the liquid makes it turn into a vapour as it evaporates.
- The vapour rises the glass tube and the thermometer shows us that the temperature is rising, as the liquid is boiling.
3)
The vapour passes through the condenser (which is kept cold) and the vapour condenses and turns back into a liquid as it passes through.
4) The liquid is collected in the beaker and the crystals of the solid is in the beaker at the begging whilst the liquid is in the end beaker.
Fractional Distillation:
- Used to separate a mixture of liquids.
- Key Point: The liquids must have different boiling points.
- Beaker, Fractionating collumn, Condesner therometer.
Fractionating Collum= Full of little glass rods + Cooler at top than bottom.
Fractional Distilation Method:
1) Heat the mixture to about the lowest chemicals boiling point.
2) Evaporates + rises up fractionating collum and passes into the condenser and condense back into a liquid into beaker.
3) By chance some of the higher boiling point liquids may evaporate however as they rise up the fractional collum and come into contact with the rods (which are cooler than boiling point) they condense into liquid and into the beaker.
4) Only liquid is the lowest boiling point.
Repeat by raising the temperature of the higher boiling point liquid.
Additional Information:
- If two chemicals have very similar boiling points, it is much harder to seperate them.
- Several rounds of fractional distilation may need to be carried out.
- Using fractional distliation for a greater volume of chemical requires different equipment although the principle stays the same.
Paper Chromotography:
- Physical proccess.
- Allows us to seperate substances based on different solubilities.
- 1) Take a piece of chromatography paper and draw a pencil line near the bottom.
2) Place a dot of ink on the pencil line.
3) Place the bottom of the paper in a solvent (A liquid that dissolves substances).
4) The solvent makes it way up the paper and dissolves the ink of the 2 substances and is carried up the paper.
Paper= stationary phase because it does not move.
Solvent= Moving phase because it does move.
If the substance has 1 dot, this means that it is a pure substance, but if it has more than 1 spot this means that it is a mixture.
Additional information:
- It works because each chemical in the mixture will be attracted to the stationary phase (the paper) to a different extent.
- Chemicals that are strongly attracted to the stationary phase will not move very far.
- Chemicals that are weakly attracted move further up the paper.
- We draw the line with pencil and not pen because the pen ink would move the paper with the solvent.
Plum Pudding Model:
- 1897: Atoms contain tiny negative particles, called electrons.
- This showed that the atoms are not spheres that cannot be divided atoms have an internal structure.
-Plum Pudding:
- Believed that the atom was a ball of positive charge, with negative electrons embedded into it.
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What is the alpha scattering experiment?
- Scientists attempt to validate whether the plum pudding model was accurate/correct.
- Scientists took a peice of gold foil andt the reason they used gold was that it can be hammered to be only a few atoms thick.
- Scientists fired tiny particles at the gold, and these are called alpha particles, these have a positive charge.
Most of the other particles fired straight through the gold foil without changing direction. - Sometimes an alpha particle was deflected (changed direction as it passes through the gold foil)
- Sometimes an outer particle would bounce straight back off the gold foil.
results:
- As most of the alpha particles went straight through the the gold atoms suggested that atoms are mainly empty space.
- As some of the alpha particles were deflected (changed direction) that meant that:
- The centre of the atom must have a positive charge. Alpha particles that come close to this get repelled and change direction.
As some alpha particles bounced straight back:
- The centre of the atoms must contain a greater deal of mass.
- This is called the nuclues and when an alpha particle collides with it, it bounces back.
Nuclear Model:
- In result of the Alpha Scattering Experiment scienctists, replaced the plum pudding model with a nuclear model.
- Most atom is empty space.
- Centre is a positive nucleus.
- Edge has negative electrons.
- Further experiments made this model to be adjusted.
Niels Bohr:
- Electrons orbit the nucleus at specific distances, rather than in a general area.
2nd evaluation:
- These orbits are now called shells or energy levels.
- Positive charge in the nucleus is due to tiny particles called protons.
James chadwick:
- The Nucleus also contains neutral particles called nuetrons.
- Atoms have no overall charge.
- because number of electrons is the same as number of protons.
- ## Positive charge of the protons is cancelled by the negative charge of electrons.
different sizes of the different parts of an atom:
- Radius of an Atom: 0.1nm.
- 1x 10^-10 m.
- Some atoms are larger than others so this is an approximate figure.
Radius of a Nucleus:
- 1 x 10^-14m
Relative Charge and Relative Mass:
Protons: Relative charge= +1 Relative mass= 1 Nuetrons: Relative Charge=0 Relative Mass= 1 Electrons: Relative Charge=-1 Relative Mass= very small.
“Atomic Number and Mass Number”
Atomic Number= Number of Protons.
Large Number= Mass Number- Total Number of protons and neutrons.
What is an Isotope?
- Atoms of an element with different number of neutrons.
- ## All atoms of an element have the same number of protons.
What is a ion?
- Ions are atoms that have an overall charge.
- This is because they have gained or lost electrons.
Positive Ions have lost an electron.
Negative Ions have gained an electron.
Relative atomic Mass:
- The relative atomic mass is the average of the mass numbers of the different isotopes.
- Weighted for the abundance of each isotope(how common each isotope is).
How do we calculate this?
relative atomic mass=( Mass number of isotope 1 x percentage abundance of isotope 1) + (Mass number of isotope 2 x percentage abundance of isotope 2)/ 100
=
