C4 Chemical Patterns (OCR 21st Century Additional Science), OCR 21st Century Science: C4
What is the charge on all (a) Group 1 and (b) Group 7 elements? Explain this.
(a) group 1 elements form ions with a +1 charge because they lose the 1 electron they have in their outer shell (b) group 7 elements form ions with a -1 charge because gain an electron to add to the 7 they already have in their outershell.
What colours are produced What colours are produced when (a) lithium (b) sodium and (c) potassium are heated?
(a) lithium = red (b) sodium = yellow/orange (c) potassium = lilac
As you go down Group 7 what happens to (a) reactivity (b) melting point and (c) boiling point?
(a) reactivity decreases (b) melting point increases (c) boiling point increases
As you go down Group 1 what happens to (a) reactivity (b) density (c) melting point and (d) boiling point?
(a) reactivity increases (b) density increases (c) melting point decreases (d) boiling point decreases
Write a symbol equation for the reaction of iron with iodine. (make sure you can do this for any Group 7 element).
2Fe + 3I₂ → 2FeI₃
Write a symbol equation for the reaction of lithium with chlorine (make sure you can do this for any Group 1 and Group 7 element).
2Li + Cl₂ → 2LiCl
What is a displacement reaction?
A displacement reaction is where a more reactive element displaces (pushes out) a less reactive element from a compound
How does the reactivity of group 1 metals change as you go down the group?
Alkali metals get more reactive as you get further down the group
Lithium, sodium, potassium, rubidium, caesium and francium are all group 1 metals. How many electrons do they have in their outer shell?
All have one electron in there outer shell. Why do group 1 metals become more reactive as you go down the group?: They are more reactive as you go down as the outer electron is more easily lost being further away from the nucleus. Also as they go down they have a higher density and lower melting point and boiling point. What flame colours do lihtium, sodium and potassium have?: Element Symbol Flame colour lithium Li red sodium Na yellow potassium K lilac
What is an ion and how are they formed?
An ion is a charged particle of group or particles. They are formed when atoms gain or lose electrons.
What changes as you go across a period on a periodic table?
As you go across the period the numbers of protons and electrons. Periods show the filling of each shell with electrons. So all elements in a period have the same number of electron shells.
Explain the trend in reactivity as you go down Group 1
As you go down the group the outer electron is lost more easily becuase its further away from the nucleus
What is the key thing in which atoms of each element differ from each other?
Atoms of each element have different proton numbers. FYI The number of electrons can change depending on bonding and the number of neutrons even varies for atoms of the same element (isotopes.)
How was helium discovered? Or How do you identify elements without a chemical test?
Bunsen invented the Bunsen burner that is still used in labs today. He realized different chemicals produced different flame colours. Spectroscopy was used to record the line spectra of elements. Janssen and Lockyer discovered helium when they were studying the line spectra of the elements in the Sun during an eclipse.
What are the properties of group 1 metals?
Can be cut with a knife Shiny, but tarnish quickly with air, because a layer of oxide is formed Good conductors of electricity (Like all metals) Low density Low melting point
What are some everyday uses of chlorine?
Chlorine is used in plastics such as PVC. Chlorine is used in water treatment, but can damage the environment if they leak into the natural environment, for example CFC's effect the concentration of ozone in the upper atmosphere. FYI Bromine is found in the sea, but liquid bromine is extremely corrosive. Bromine can be used in medical drugs and pesticides. Iodine is needed in the human diet in small amounts to prevent disease of the thyroid, so it is often added to salt and water. Iodine is used in the manufacture of medicines, photographic chemicals and dyes.
Why do different elements produce different line spectrums?
Different elements produce different wavelengths of light because they have different electron arrangements.
What is the molecular formula of iron (III) bromide? (note: iron (III) = Fe³⁺)
FeBr₃
What is the molecular formula of iron (II) sulfate? (note: iron (II) = Fe²⁺; sulfate = SO₄²⁻)
FeSO₄
What is the maximum number of electrons allowed in the first, second and third electron shells?
First shell = maximum of 2 Second shell = maximum of 8 Third shell = maximum of 8
Describe how Group 1 elements react with chlorine and state what is produced.
Group 1 elements react vigorously with chlorine to produce salts (e.g. sodium chloride)
What is the appearance of group 1 metal chlorides, and do they dissolve in water?
Group 1 metal chlorides are salts that are colourless, crystalline and dissolve in water
Explain the trend in reactivity as you go down Group 7.
Group 7 eleemtns have 7 electrons in the outer shell and gain an electron when they react. As you go down the group the outer shell electrons are further away from the nucleus so it is harder to attract additional electrons.
What does the group number in the periodic table tell us about the arrangement of electrons in a atom?
Group number = number of electrons in the outershell (e.g. carbon has the electron arrangement 2, 4. It is in group 4 and has 4 electrons in its outer shell)
Describe the role of Dobereiner in the development of the perodic table.
Grouped elements in 3s based on properties and relative atomic mass. He noticed that the relative atomic mass of the middle element was the average of the other 2.
What do all elements in the same group have in common and what is the result of this?
Groups have the same number of electrons in their outer shell, which gives them similar properties.
In general elements with one or two electrons in the outer shell are metals. What are the exceptions?
Helium which is a noble gas Hydrogen which has some properties of metals and some of non-metals but is usually classified as a non-metal.
How are elctrons arranged in an atom?
In shells surrounding the nucleus
Why do solid ionic substances not conduct electricity but liquid ionic substances do?
In solid ionic substances the ions are not free to move so cannot conduct electricity. In liquid ionic substances the ions are free to move so can conduct electricity.
If the electron arrangement of carbon can be written as 2, 4 what is the electron arrangement of sodium?
It has 11 electrons in total so its electron arrangement is 2, 8, 1
What is the molecular formula potassium chloride?
KCl
What can line spectrums be used for?
Line spectrums can be used to identify elements
What is the product of a group 1 metal reacting with chlorine(e.g. Lithium)?
Lithium + chlorine --> lithium chloride
What are the products of a group 1 metal reacting with water (e.g. Lithium)?
Lithium + water --> lithium hydroxide + hydrogen
What sort of boiling and melting point do the halogens have?
Low melting and boiling points because of weak forces of attraction between the molecules.
How is the modern day periodic table different from the one made by Mendeleev?
Mendeleev's table = elements in order of relative atomic mass Modern day table = elements in order of atomic number
Ionic bonds exist between which two types of elements?
Metals and non-metals
What is the molecular formula of sodium fluoride?
NaF
State if a reaction will occur between iodine and lithium bromide and explain your answer.
No becuase iodine is less reactive than bromine
Why are noble gases very unreactive?
Noble gases are very unreactive because they have a full outer shell
Where are the protons and neutrons found?
Nucleus
Work out the charge of the oxygen ion in Na₂O if the charge on a sodium ion is +1.
O²⁻
What does the period number in the periodic table tell us about the arrangement of electrons in a atom?
Period number = number of electron shells that are occupied. (e.g. carbon has the electron arrangement 2, 4. It is in period 2 and its electrons occupy 2 electron shells)
How are the elements ordered in the periodic table?
Periodic tables show the atoms in order of proton number instead of Relative Atomic Mass₃
The number of which particle decides what element an atom is?
Proton (e.g. all carbon atoms have 6 protons, all oxygen atoms have 8 protons)
Describe the role of Mendeleev in the development of the perodic table and state why this was criticised.
Put elements in order of relative atomic mass. To make sure that all groups contained only elements with similar properties he: (1) left gaps for undiscovered elements (2) changed the order of some elements
Describe the role of Newlands in the development of the perodic table and state why this was criticised.
Put elements in rows of 7 in order of relative atomic mass. He said that every 8th element had similar properties. His work was criticised because some of his groups contained elements that didn't have similar properties (e.g. he had metals and non-metals in the same group).
What precautions should be taken to ensure that group 1 elements (alkali metals) do not come into contact with water?
Should be stored under oil and not touched with skin
Write a balanced symbol equation for the reaction between sodium and chlorine to form sodium chloride
Sodium + chlorine → sodium chloride 2Na(s) + Cl₂(g) → 2NaCl(s)
How reactive are the group 1 metals and what happens when they react with water?
The alkali metals are reactive metals found in group one of the periodic table that react with water to form alkaline solutions.
What are the halogen all found in group 7 have in common?
The halogens all have 7 electrons in their outer shell. They all make molecules with pairs of atoms.
What are the colours of all the halogens?
The halogens are all coloured Fluorine is a yellow gas Chlorine is a dense green gas Bromine is a dense red/brown volatile liquid Iodine is a dark grey solid with a purple vapour When they are in salts/exist as ions they are colourless.
What are the halogens?
The halogens are very reactive non-metals found in group 7 of the periodic table. FYI Halogen means salt former, and the halogen elements form salts when they react with metals.
How does the reactivity of the halogens change as you go down the group?
The halogens get less reactive as you go further down the group on the periodic table.
What is atomic mass?
The number of protons + the number of neutrons
Atoms do not have any overall charge. What does this tell us about the number of protons (positive) and electrons (negative) in an atom.
The number of protons and electrons must be the same (e.g. carbon has 6 protons so it must have 6 electrons)
Why do elements in a verticle column (group) have similar properties?
They all have the same number of electrons in their outer shell.
Describe what group 1 metals look like when cut
They are shiny but quickly go dull again as they react with oxygen in the air.
What hazard is common to all group 7 elements (halogens) and what precaution should be taken when working with them?
They are very poisonous vapours so should be used inside a fume hood.
How does the reactivity of the halogens change as you go down group 7
They become less reactive as you go down as the outer shell is further away from the nucleus making the attraction weaker.
What kind of molecules do the halogens form? Give the molecular formula of chlorine to illustrate your answer.
They form diatomic molecules which are pairs of atoms e.g. Cl₂
Describe how lithium sodium and potassium react with water.
They move around the surface fizzing
How are the halogens bonded when they exist as elements?
They normally come in pairs (Cl₂, Br₂, I₂) and have a single covalent bond between them.
What are the observable signs of reaction when a group 1 metal reacts with water?
They react very vigorously and when put in water fizz/bubble/effervesce and move around, and the metal will disappear (due to having completely reacted) Potassium gets hot enough it ignites. If universal indicator is added to the solution it will turn blue/purple due to the solution becoming alkaline as a hydroxide of the metal is formed.
How can you test to show that hydrogen is given off when a group 1 metal reacts with water?
Use a lit splint and a squeaky pop will be heard
Some elements emit distinctive colours when heated, this is how fireworks get their colours. These can be used to identify a metal in a compound. What technique can we use to distinguish between two red flames from different element?
Using spectroscopy we can obtain line spectra. FYI We see colours because when heated the electrons release energy as light these can be recorded in a spectrum. Different element emit different wave lengths, therefore it can be used to identify elements. This technique is called spectroscopy.
Why do some elements produce light when heated?
When heated the electrons become 'excited' and released energy as light
Why are group 1 metals called 'alkali metals'?
When they react with water they produce hydroxides (e.g. sodium hydroxide) which are alkalis.
A more reactive halogen will displace less reactive ones, by pushing out or taking the place of the less reactive halogen within a compound. Will fluorine replace chlorine in sodium chloride?
Yes. Because fluorine is more reactive than chlorine.
What is the overall charge on ionic compounds?
Zero (becuase the charges balance each other out)
A periodic pattern is
a repeating pattern.
On a periodic table a group is a
column, and contains elements with similar properties.
Write a word equation for the reaction of fluorine and sodium bromide.
fluorine + sodium bromide → bromine + sodium fluoride
Where are the group called the alkali metals found on the periodic table?
group 1
Relative atomic masses
is the mass relative to 1/12th the mass of a carbon atom It is also often equal to the sum of the number of protons plus neutrons
The periodic table is arranged by
proton number
On a periodic table a period is a
row FYI: It will often start with a reactive metal and ends with a noble gas.
Write the word and symbol equation for the reaction of sodium with water (make sure you can do this for any group 1 element).
sodium + water → sodium hydroxide + hydrogen 2Na + 2H₂O → 2NaOH + H₂