GCSE Chemistry - AQA Single Science > Atoms, Elements and the Periodic Table > Flashcards
Atoms, Elements and the Periodic Table Flashcards
The periodic table shows us all the ________.
elements
The periodic table shows us all the elements.
What is the definition of an element?
In an element, all the atoms are the same.
In an element, all the _____ are the ____.
atoms
same
In an element, all the atoms are the same.
What is the definition of a compound?
Compounds contain two or more different elements chemically combined in a fixed proportion.
Compounds contain two or more _________ elements __________ ________ in a _____ __________.
different
chemically combined
fixed proportion
Compounds contain two or more different elements chemically combined in a fixed proportion.
How do the properties of compounds differ to the elements they’re made from?
Compounds usually have totally different properties to the elements they’re made from.
Compounds usually have _______ _________ _________ to the elements they’re made from.
totally different properties
Compounds usually have totally different properties to the elements they’re made from.
What do we need to do in order to be able to separate a compound, back into its elements?
If we want to separate a compound back into its elements, then we need to use a chemical reaction to do this.
If we want to ________ a compound back into its elements, then we need to use a ________ ________ to do this.
separate
chemical reaction
If we want to separate a compound back into its elements, then we need to use a chemical reaction to do this.
What is the definition of a mixture?
In a mixture, we have different elements or compounds not chemically combined together.
In a mixture, we have different elements or compounds ___ __________ ________ _________.
not chemically combined together
In a mixture, we have different elements or compounds not chemically combined together.
What do we use if we want to separate mixtures?
If we want to separate a mixture, then we use physical techniques rather than chemical reactions.
If wen want to separate a mixture, then we use ________ __________ rather than chemical reactions.
physical techniques
If we want to separate a mixture, then we use physical techniques rather than chemical reactions.
What is the definition of a molecule?
A molecule has any elements chemically joined.
A molecule has ___ ________ chemically combined.
any elements
A molecule has any elements chemically combined.
Understanding:
An atom is the ________ ____ of an element.
In an element, all the _____ are the ____.
Compounds contain ___ or ____ ________ chemically combined in a fixed proportion.
This means compounds contain the atoms of different elements (which are the same for each type of element) __________ ________ together.
A mixture has different ________ (same atoms) or _________ (these atoms of two or more different elements joined together), ___ __________ ________ together.
A molecule has ___ ________ (an element has the same atoms), chemically combined together.
Ismallest unit
atoms
same
two or more elements
chemically combined
elements
compounds
not chemically combined
any elements
What does a chemical formula tell us?
- the elements in a molecule
- the number of atoms of each element
What can we tell about the compound from this chemical formula?
ZnCO3
1 atom of zinc, 1 atom of carbon, 3 atoms of oxygen
- From this formula we can tell that there are 3 elements: zinc, copper and oxygen.
- The number of atoms of those elements is: 1 atom of zinc, 1 atom of carbon and 3 atoms of oxygen, all bonded together.
Bonding the zinc, carbon and oxygen together in this way forms a compound, and this compound can then be used to make up the substance.
What does the full sentence say?
Physical separation techniques are used to ________ ________ only.
They cannot be used to separate the ________ __ _ ________.
All separation techniques are ________ _________.
This means they __ ___ involve chemical reactions and __ ___ __________ are made.
separate mixtures
elements in a compound
physical processes
do not
no new substances
Physical separation techniques are used to separate mixtures only.
They cannot be used to separate the elements in a compound.
All separation techniques are physical processes.
This means they do not involve chemical reactions and no new substances are made.
Physical Separation Technique - Filtration:
🍵 What is filtration used for and what are the steps?
- What about the state symbol of the solid?
What is it used for -
Filtration is used to separate an insoluble solid from a liquid.
What are the steps -
1 - Use a filter funnel and filter paper (inside a beaker or conical flask)
2 - Pour the mixture into the filter paper.
3 - The liquid simply passes through the tiny pores in the filter paper. The solid material can’t pass through the filter paper so it’s trapped.
4 - We now have the liquid separated from our solid.
The solid in the equation will have (s) state symbol.
Physical Separation Technique - Crystallisation:
🍵 What is crystallisation used for?
What are the steps, and how can we make the
process happen faster? What do we need to be
careful of if we use this alternative method?
- What about the state symbol of the solid?
Crystallisation is used to separate a soluble solid/salt from a liquid.
1 - Leaving the solution for a few days…
2 - The water will evaporate…
3 - Leaving behind crystals of the aqeous solid.
1 - To make it happen faster, gently heat the solution to evaporate the water.
2 - Be careful that the heating doesn’t affect the chemical you’re trying to crystallise (some chemicals break down in heating)
The solid in the equation will have (aq) state symbol.
The solid in the equation will change to (s) state symbol, because it will no longer be dissolved in water - which has evaporated forming crystals - it is now a solid.
Physical Separation Technique - Simple Distillation
🍵 What is simple distillation used for? (compare this roughly to fractional distillation hint - solid from liquid, liquid from liquid)
Describe - how does simple distillation work?
What apparatus is used to do this?
Describe - what is the method?
What it’s used for -
Simple distillation is used to separate a liquid from a solid if we want to keep the liquid.
Fractional distillation allows us to separate two different liquids.
How does it work -
1 - ☀️ First we evaporate the liquid by heating
2 - ⛸️ We then condense the vapour (back to a liquid again) by cooling
Apparatus
1 - Solution of liquid and dissolved solid inside flask.
2 - The flask is connected to a continuous glass tube, surrounded in the middle by a condenser
3 - Cold water into condenser from tap, continuously, keeping the internal glass tube cold.
Water out of condenser afterwards - it goes down the sink
4 - Thermometer connected to flask inside continuous glass tube
Describe -
1 - Heat the solution… the liquid in the solution evaporates turning into a vapour
2 - The vapour rises up the glass tube and passes into the condenser (the condenser is kept cold because cold water is being circulated around it). This means the vapour can condense back into a liquid as it passes through.
3 - Collect the liquid in the beaker.
We’re now left with crystals of the solid in the flask (because the liquid evaporated), but now we’ve also been able to collect the liquid
Physical Separation Technique - Fractional Distillation
🍵 What is fractional distillation used for?
- What is the apparatus for this type of distillation
like?
- Describe a method for fractional distillation (what
does the repeated condensing and evaporation due
to the fractionating column mean? what
does the temperature on the thermometer rising
mean, and what does it mean when it's constant?)
- What do we need to do if the mixture of liquids
contain *very similar* boiling points? How will
things work for purifying *large volumes* of liquid?
In fraction distillation, we separate a mixture of different liquids - they must have different boiling points.
Apparatus -
1 - Flask contains mixture of two (or more) different liquids with different boiling points.
2 - Flask is attached to a fractionating column made of hundreds of glass beads
3 - Thermometer at the top of the fractionating column
4 - A condenser containing circulating cold water
Method -
1 - Gently heat the mixture
2 - Both of the liquids start to evaporate. Lower boiling point evaporates more easily.
3 - A mixture of two different vapours go into fractionating column. When they hit the column, they condense back into the flask and evaporate again - the repeated evaporation and condensation leads to an
4 - The repeated evaporation and condensation leads to an increased the amount of the lower boiling point chemical in the fractionating column.
5 - Both vapours pass up the column - the lower boiling point chemical will be ahead of the higher boiling point chemical.
6 - As the warm vapours pass up they reach the thermometer. It’s temperature rises meaning a mixture of two different vapours are passing through - mixture will have more of the lower boiling point chemical, though.
7 - The vapours pass into the condenser and become drops of liquid (still a mixture of the two chemicals).
8 - The temp. on the thermometer will reach the boiling point of the first chemical and stop rising. Shows only mainly one chemical is there.
9 - It condenses and we collect it in the fresh beaker as our first fraction (pure).
10 - Thermometer temperature rising again - means a mixture of vapours is passing into the condenser - mainly contains the chemical with a higher boiling point.
11 - Once temperature becomes constant (will be at temp. of the second chemical) we now know we’re collecting a relatively pure sample of the second chemical (completely pure).
So:
1 - Vapours rise and condense but due to BP and fractionating column, when both vapours pass through it mainly contains lower BP chemical
2 - Rising temperature - a mixed solution is passing through condenser. (Mainly contains chemical of lower boiling point.) Condenses.
3 - Constant temperature - relatively pure solution condenses + is collected.
4 - Process repeats for each different chemical/liquids.
Extra things -
If two liquids have very similar boiling points, then it is much harder to separate them. We might need to carry out several rounds of fractional distillation.
Using fractional distillation to purify large volumes of liquid (e.g. crude oil) requires different equipment although the principle is the sane.
Physical Separation Technique - Chromatography
🍵 What does paper chromatography allow us to do?
- What paper do we use?
- What method is used?
- What is the stationary & mobile phase?
- What are two examples of results?
- What are the two important points (chemicals’
attraction to stationary phase and what happens to
a pure chemical and the chemicals in a mixture)
Paper chromatography allows us to separate substances based on their different solubilities.
Say we had some coloured pens - it helps us know which ones:
- contain only one colour
- contain a mixture of colours.
Method:
- Use a peice of chromatography paper.
- Draw pencil line near bottom.
- Put a dot of first colour on the pencil line.
- Put a dot of second colour next to that.
- Can do this for several colours as long as there’s enough space.
- Place bottom of paper into solvent (a liquid that will dissolve substances. There’s lots of different solvents)
- Solvent makes its way up the paper.
- Solvent dissolves the ink in the two coloured dots.
- These are now carried up as well.
- —> Paper = Stationary phase. Does not move.
- —> Solvent = Mobile phase. Does move.
Results:
- Colour A (like red) may form a single spot. One spot means it is a single pure substance.
- Colour B (like green) may have separated into two different spots. This means it is a mixture of two different substances.
Important point 1 (starts using the phrase ‘chemical’)
Why does it work? It works because…
• Each chemical is attracted to the stationary phase to a different extent.….
Strong attraction to stationary phase = not move very far.
Weak attraction to stationary phase = move further up paper.
Important point 2 -
Pure chemical = single spot in all solvents although the position of the spot may change.
Chemicals in a mixture = may separate into different spots depending on solvent.
Why do we draw our starting line in pencil?
So that pen ink does not move up the paper with the solvent.
☕ What are the early ideas of the structure of atoms?
(plum pudding model)
☕ What was the alpha-scattering experiment? Describe how it was used to work out the nuclear model of atomic structure, the currently accepted model (what are the three features of it?)
- the nuclear model is our current model, but it did get adjusted in further years too…
Early ideas:
➜ Ancient Greeks: everything is made of atoms which are tiny spheres that cannot be divided
Electrons:
➜ 1987 Scientists discovered - atoms contain tiny negative particles called electrons.
➜ So atoms are not tiny spheres that cannot be divided. Atoms must have an internal structure!
Therefore, scientists suggested a different model for the structure of atoms - the plum pudding model, which suggested this structure of atoms:
➜ Ball of positive charge
➜ Negative electrons embedded
To test this…
Alpha scattering experiment:
- Gold foil (used gold because we can hammer it into very thin foil just a few atoms thick)
- Fired alpha particles (positive charged) at gold foil
Results:
➜ Straight through = atoms are mainly empty space
➜ Deflected (changed direction after passing through) = centre must have positive charge. Alpha particles that come close to this (the positive charge around the centre) are repelled and change direction.
➜ Reflected, bounced straight back = Centre of atom must contain great deal of mass. We now call that central part, the nucleus. Alpha particles that collide directly with nucleus bounce straight back.
So the model of atomic structure become replaced from plum pudding, to nuclear model (current) -
- Mostly empty space
- Centre has tiny positive nucleus
- Negative electrons are around edge
This model did get adjusted further…
Hello again :)
☕ What is the nuclear model of atomic structure?
☕ How was the nuclear model adjusted by the discovery of:
- Electron energy levels
- The proton
- The neutron
Replaced nuclear model:
- mostly empty space
- centre has positive nucleus
- Negative electrons around edge
This model is current.
Further discoveries were made causing the model to be adjusted…
Bohr:
○ Electrons orbit the nucleus at specific distances.
○ Bohr’s work agreed with the results of experiments other scientists*.
○ We now call the ‘orbits’ energy levels or shells.
(This is what our current model of electron energy levels/shells looks like)
Protons:
○ Scientists discovered that the positive charge in the nucleus is due to the tiny positive particles called ‘protons’.
Chadwick:
○ The nucleus also contains neutral particles called neutrons.
Atoms:
○ Atoms have no overall charge.
○ This is because the number of electrons is the same as the number of protons. (so their charges will cancel out)
Atom sizes:
Radius of atom = 1 x 10^-10 m
Radius of nucleus = 1 x 10^-14 m
Relative charge and relative mass: 'Relative charge' means the charge of one particle compared to another particle. ○ Protons = relative charge of +1 ○ Neutrons = relative charge of 0 ○ Electrons = relative charge of -1
Relative mass:
○ Protons = 1
○ Neutrons = 1
(They both have a relative mass of 1, telling us that
protons and neutrons have the same mass)
○ Electrons = very small or 0.00050
📝 Hi! Please answer fully - How do we use the atomic number and mass number to work out the number of protons, neutrons and electrons in the: - atoms of an element? - isotopes? - ions?
Answer each of these carefully :)
So, atoms contain:
○ A central nucleus surrounded by electrons (negative charge).
○ In the nucleus we find protons (positive charge) and neutrons (neutral).
○ Atoms have no overall charge because the number of electrons is the same as the number of protons.
The positive charges on the protons are cancelled by the negative charges on the electrons.
📝 The periodic table shows us all the elements.
○ We can use it to work out the number of protons,
neutrons and electrons of the -atoms of each
element.-
Atomic number and mass number:
Atomic number = number of protons in the atoms of that element.
Mass number = total number of protons and neutrons added together.
- Number of electrons in an atom is the same as the number of protons.
- Number of neutrons = mass number - atomic number
E.g. atoms of lithium contain 3 protons, 4 neutrons and 3 electrons… (most atoms of lithium contain 4 neutrons, but some atoms contain a different number of neutrons and we call -all- of these versions of lithium isotopes)
Isotopes:
○ Isotopes are atoms of an element with different numbers of neutrons.
○ All atoms of an element have the same number of protons.
Finding the number of neutrons of an isotope:
Look at the different mass numbers and calculate the number of neutrons in each particular isotope.
Ions:
Ions are atoms which have an overall charge.
This is because they have gained or lost electrons.
- Positive ions have lost electrons.
- Negative ions have gained electrons.
Finding the number of electrons of an ION:
The electrons of an ion will be different to it’s proton number because the atom has lost or gained electrons. Here, look at the charge to find out what the number of electrons is (because it is no longer equal to the proton number).
📝 What is meant by relative atomic mass?
📝 How do we calculate the relative atomic mass for an element?
What is meant by relative atomic mass?
○ The relative atomic mass is the average of the mass numbers of the different isotopes.
○ The relative atomic mass is weighted for the abundance of each isotope.
How do we calculate the relative atomic mass for an element (btw - this average is needed since isotopes will have different mass numbers individually, so we need an overall relative atomic mass for the element)
○ Relative atomic mass = ((mass number of isotope 1 * abundance of isotope 1) + (mass number of isotope 2 * abundance of isotope 2)) / 100
📝Hi - please answer fully:
○ How do we work out the electronic structure of elements?
○ How can we use this to work out the group number in the periodic table?
We can work out the electronic structure of an element by looking at the atomic number, which tells us the protons and electrons.
○ Electrons exist in energy levels (shells)
○ Each energy level can hold a maximum number of electrons: First = 2, Second and third = 8, Fourth = 18
2, 8, 8, 18 (not 10)
Writing it:
○ Look at the atomic number to find out the number of protons in the atoms of the element.
○ Using the fact each energy level can hold a maximum number of electrons, draw out the electrons in the atoms of that element.
Development of the periodic table:
○ What were the early attempts to rearrange the elements in the periodic table?
○ Why did Dmitri Mendeleev’s periodic table successfully predict the properties of the elements?
○ How are the elements arranged in the modern periodic table?
Modern periodic table:
○ Arranged in groups
○ We have group 1 and group 2, then the Transition elements and groups 3, 4, 5, 6, 7, and group 0
Name:
○ It’s called the periodic table because periodic means occurring at regular intervals.
○ Elements with similar properties occur at regular intervals.
○ Group 1 consists of highly reactive metals - lithium, sodium and potassium
○ Group 7 consists of highly reactive non-metals - fluorine, chlorine and bromine
Modern Group Arrangement:
The elements in a group have similar chemical properties.
That means they react in a similar way.
This is because all the elements in a group have the same number of electrons in their outer energy level.
Scientists who made early attempts to arrange the elements into an order:
- Johann Dobereiner —> elements with similar chemical properties occurred in threes which he called ‘triads’ - e.g. lithium, sodium and potassium they react rapidly with water as well as chlorine, bromine and iodine.
- -> Scientists started wondering whether elements could be arranged into a logical order
- John Newlands = INCREASING ATOMIC WEIGHT
- law of octaves ——— every eight element reacts in a similar way (E.g. lithium, sodium and potassium, in his table!)
- if you go downwards, these are each 8th element and they react in similar ways to each other.
○ His system had some problems - by always sticking to the exact order of atomic weight some elements were grouped with totally different properties
○ So it wasn’t taken seriously by other scientists
Dmitri Mendeleev:
First modern periodic table
1 - Increasing atomic weight
2 - switched the order of specific elements, so they fitted patterns of other elements in the same group
3 - Some elements not been discovered so left gaps where he thought it was missing
4 - Confident his table was correct he predicted properties of these undiscovered elements based on other elements in the same groups.
5 - They were discovered and their properties matched his predictions.
6 - Due to this, other scientists accepted his table was correct.
Modern periodic table:
A couple of differences although almost exactly the same as Mendeleev’s.
○ Elements are arranged in order of atomic number or protons, because they had not been discovered them. He ordered them in atomic weight but the problem is that elements can appear in the wrong order because of the presence of isotopes (I imagine this changes the mass number affecting the atomic weight)
The modern periodic table has group 0, the noble gases Again, these had not been fully discovered when Mendeleev published his table.
