Atomic structure and the periodic table 1 Flashcards
Atoms, elements, compounds, and mixtures.
What are all substances made of?
Atoms
What is an atom?
The smallest part of an element that can exist. (and still be identified as that element).
What do chemical symbols represent?
Atoms of each element.
What does the chemical symbol ‘O’ represent?
An atom of oxygen.
What does the chemical symbol ‘Na’ represent?
An atom of sodium.
How many different elements are there?
about 100
Where are elements shown?
The periodic table.
How are compounds formed?
From elements by chemical reactions.
What do chemical reactions always involve?
The formation of one or more new substances.
What do chemical reactions often involve?
A detectable energy change.
What is a compound?
A chemical substance containing two or more elements that are chemically combined in fixed proportions.
How can compounds be separated into elements?
Only by chemical reactions.
How can compounds be represented?
By formulae using the symbols of the atoms from which they were formed.
How can chemical reactions be represented?
-Word equations
-Equations using symbols and formulae
Formula for ammonia
NH₃
Formula for sodium chloride
NaCl
Formula for carbon monoxide
CO
Formula for hydrochloric acid
HCl
Formula for calcium chloride
CaCl₂
Formula for sodium carbonate
Na₂CO₃
Formula for sulfuric acid
H₂SO₄
What are the molecules on the left hand side of an equation called?
Reactants
What are the molecules on the right hand side of an equation called?
Products
You need to be able to write what?
Balanced half equations and ionic equations where appropriate.
What do symbol equations show?
The symbols/formulas of the reactants and products.
What are the steps to balancing symbol equations?
1-Find an element that doesn’t balance and pencil in a number to try and sort it out.
2- If it creates another imbalance, pencil in another number and see where that gets you.
3- Carry on until the equation sorts itself out and becomes balanced.
4- You can always draw dots or the symbol repeats if necessary.
What is a mixture?
A substance that consists of two or more elements or compounds not chemically combined together.
What happens to the chemical properties of two substances that are mixed together?
They are unchanged.
How can mixtures be separated?
By physical processes such as filtration, crystallisation, simple distillation, fractional distillation, and chromatography.
What happens during physical separation techniques?
No new substances are made.
No chemical reactions occur.
What is air?
A mixture of gases - mainly nitrogen (78%) , oxygen, carbon dioxide, and argon.
What is crude oil?
A mixture of different length hydrocarbon molecules.
What is chromatography used for?
Separating different dyes in an ink.
Chromatography
Steps 1,2, and 3
1- Get a piece of filter paper and draw a horizontal line near the bottom using a pencil.
2- Add a spot of ink to the line
3- Place the filter paper in a beaker of shallow solvent e.g. water, ethanol, making sure the ink isn’t touching the solvent.
Explain why you shouldn’t use a pen to draw a line on the filter paper for paper chromatography.
The pen ink might dissolve in the solvent and rise up the filter paper.
Chromatography
steps 4, and 5
4- Place a lid on top of the beaker to stop the solvent evaporating.
5- The solvent will seep up the up the paper, carrying the ink with it.
Why do we not want our spot of ink to be in the solvent?
Because then the ink would dissolve into the solvent.
What does the solvent used in chromatography depend on?
What’s being tested.
Some compounds dissolve well in water but some don’t.
In which case other solvents like ethanol are needed.
Chromatography
Step 6
6 - Each different dye in the ink will move up the paper at a different rate so the dyes will separate out.
Pencil marks are…
…insoluble so won’t dissolve in the solvent.
What will happen if dyes in the ink are insoluble in the solvent you’ve used for paper chromatography?
They will stay on the baseline.
Chromatography
step 7
7 - Take the filter paper out of the beaker when the solvent has nearly reached the top of the paper. Leave it to dry.
What is the end result of a paper chromatography experiment?
A pattern of spots called a chromatogram.
What is filtration used to separate?
Insoluble solids from liquids.
How can filtration be used in purification?
Solid impurities in a reaction mixture can be separated out.
Insoluble
Can’t be dissolved in a liquid.
Briefly describe the process of filtration.
Filter paper is folded into a cone shape and placed into a filter funnel.
This is positioned over a beaker.
A mixture of liquids and insoluble solids is poured into the filter funnel.
The solid is left in the filter paper and the liquid will pass through.
How does filtration work?
The filter paper has tiny holes in it. These are large enough to let small molecules and dissolved ions through, but not the much larger particles of undissolved solid.
What is evaporation used to separate?
Soluble solids from solutions.
What is crystallisation used to separate?
Soluble solids from solutions/liquids.
If a solid is dissolvable, it’s called what?
A soluble solid.