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 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.
If a solid is dissolvable, it’s called what?
A soluble solid.
Evaporation steps 1 and 2
1- Pour the solution into an evaporating dish and gently heat over a bunsen burner/in a water bath.
2.The solvent will evaporate and the solution will get more concentrated.
Evaporation steps 3 and 4
3-Eventually, crystals will start to form.
4- Keep heating the evaporating dish until all you have left are dry crystals.
For evaporation, what apparatus can be used instead of a Bunsen burner to heat a solution?
-A water bath
-An electric heater
Evaporation positive
It’s a really quick way of separating a soluble salt from a solution.
Evaporation negative
You can only use it if the salt doesn’t decompose when it’s heated.
Otherwise, you have to use crystallisation.
Which method produces bigger crystals: evaporation or crystallisation?
Crystallisation