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
Crystallisation 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.
Crystallisation step 3
3- Remove the dish from the heat once some of the solvent has evaporated, or when you see crystals start to form.
Leave the solution to cool.
What is ‘the point of crystallisation’?
When you can see crystals start to form.
Crystallisation steps 4 and 5
4- The salt should start to form crystals as it becomes insoluble in the cold and highly concentrated solution.
5-Filter the crystals out of the solution, and leave them in a warm place to dry.
For crystallisation, what apparatus can be used instead of a ‘warm place’ so that the crystals can dry?
-A drying oven
-A desiccator
What is rock salt?
A mixture of salt and sand.
Similarities between salt and sand.
They are both compounds.
Differences in physical properties of salt and sand.
Salt dissolves in water but sand doesn’t.
Why might we grind rock salt?
To make the salt crystals small so that they will dissolve easily.
(This is step 1 in separating rock salt. )
Separating rock salt step 2
2- Put the mixture in water and stir. The salt will dissolve, but the sand won’t.
Separating rock salt step 3
3- Filter the mixture. The grains of sand won’t fit through the tiny holes in the filter paper, so they collect on the paper.
The salt passes through the paper as it’s part of the solution.
Separating rock salt step 4
4- Evaporate the water from the salt so that it forms dry crystals.
For larger crystals. use crystallisation.
What properties will a mixture of iron powder and sulfur powder have?
It will have the properties of both iron and sulfur:
-Grey magnetic bits of iron
-Bright yellow bits of sulfur
What is distillation used to separate?
A liquid from a solution.
What is the problem with simple distillation?
It can only be used to separate liquids with very different boiling points.
If the temperature goes higher than the boiling point of the substance with the higher boiling point, they will mix again.
What is fractional distillation used to separate?
A mixture of liquids (even with similar boiling points).
Briefly describe the process of simple distillation.
A solution is heated. The part of the solution with the lowest boiling point evaporates first.
The vapour is then cooled in a condenser and condenses. It is collected in a beaker.
The rest of the solution is left behind in the flask.
When explaining/describing methods of separating mixtures…
DRAW ANNOTATED DIAGRAMS!
Simple distillation example
You can use simple distillation to get pure water from seawater.
The water evaporates and is condensed and collected.
Eventually you’ll end up with just the salt left in the flask.
Fractional distillation steps 1 and 2
1- Put your mixture into a flask and place a fractionating column on top. Heat.
2-The different liquids will all have different boiling points so will evaporate at different temperatures.
Fractional distillation steps 3 and 4
3- The liquid with the lowest boiling point evaporates first.
When the temperature on the thermometer matches the boiling point of this liquid , the liquid will reach the top of the column.
4-The vapour is then cooled in a condenser and condenses. It is collected in a beaker.
Fractional distillation step 5
5- At the same time, liquids with higher boiling points may also start to evaporate.
However, the fractionating column is cooler towards the top.
This means that they will only get part of the way up before condensing and running back down towards the flask.
Fractional distillation step 6 (final step)
6 - Once the first liquid has been collected, you raise the temperature until the next one reaches the top.
Give an example of a mixture separated using fractional distillation
Crude oil
In fractional distillation, what are the separated substances called?
Fractions
What are the subatomic particles found in an atom?
Protons
Neutrons
Electrons
What is the relative electrical charge of a proton?
+1
What is the relative electrical charge of a neutron?
0
What is the relative electrical charge of an electron?
-1
What is the overall electric charge of an atom?
Atoms have no overall electric charge.
In an atom, the number of electrons is equal to what?
The number of protons in the nucleus.
What does the atomic number of an element tell us?
The number of protons in one atom of that element.
What differs between atoms of different elements?
The number of protons.
(This determines what the element is).
All atoms of a particular element have what in common?
They have the same number of
protons.
How large are atoms.
Very small, about 1 x 10 -10 m
0.1 nm in standard form (in m).
1 x 10⁻¹⁰ m
How large is the radius of an atom’s nucleus?
1 x 10⁻¹⁴ m
(less than 1/10 000 of that of the atom)
Where is almost all of the mass of an atom concentrated?
In the nucleus.
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
Very small
What does the mass number show?
The sum of the protons and neutrons in an atom.
What are isotopes?
Atoms of the same element with different numbers of neutrons.
Which is the top number on your periodic table: mass or atomic number?
Mass number (think massive as it’s always the larger number).
How do we calculate the number of neutrons in an atom?
Mass number - Atomic number
Which is the atomic number on your periodic table: the top or bottom number?
The bottom one.
1nm in standard form
1 x 10⁻⁹ m
What is the charge of a nucleus?
Positive
What is an ion?
An atom or group of atoms that has lost or gained electrons.
Why do ions have an overall charge?
The number of protons doesn’t equal the number of electrons.
Why do charges cancel out in an atom?
The charge on the electrons is the same size as the charge on the protons, but opposite - so the charges cancel out.
What factor determines the size of an atom?
The volume of electron orbits.
What do electrons do? (normally)
Orbit the nucleus of an atom in electron shells.
Pb is the shorthand for what in chemistry?
Lead
Give an example of a pair of isotopes.
Carbon-12 and Carbon-13.
Carbon-12 has 6 protons, 6 electrons, and 6 neutrons.
Carbon-13 has 6 protons, 6 electrons, and 7 neutrons.
What is the relative atomic mass of an element?
An average mass that takes account of the different masses and abundances of the isotopes of an element.
What is the formula for relative atomic mass?
Ar =
∑(isotope abundance x isotope mass number)
÷
sum of abundances of all the isotopes
The electrons in an atom occupy what?
The lowest available energy levels
(innermost available shells, closest to the nucleus).
The electronic structure of an atom is known as what?
The electronic configuration.
What is the maximum number of electrons in the first electron shell?
2
What is the maximum number of electrons in the second, third, fourth etc. electron shell?
8
The electronic structure of an atom can
be represented by what?
- numbers
-a diagram
What is the electronic structure of sodium?
2, 8, 1
Why do atoms react?
To gain a full outer shell of electrons and become stable.
In which direction do we draw the crosses on electron configuration diagrams?
Clockwise from North.
What is the aim of the separating mixtures practical?
To produce a pure, dry sample of a soluble salt from an insoluble oxide or carbonate.
What is the symbol equation for the reaction of Copper (II) Oxide and sulfuric acid? (rp)
CuO (s) + H₂SO₄ (aq) → CuSO₄ (aq) + H₂O (l)
What is copper (II) oxide?
A black powder (that forms blue ions)
Metal oxides are…
insoluble bases
How may we remove excess copper (II) sulfate from copper sulfate solution?
Filtration
What colour are copper (II) sulfate crystals?
Bright blue
(rhombus shaped)
