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The periodic table - Coggle Diagram
The periodic table
Group 1 - alkali metals
Properties
Very low densities compared to most metals. Lithium, sodium and potassium float on water as their density is less than 1g/cm3
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Silvery, shiny surface when first cut but go dull very quickly as they oxidise
In a jar of oxygen, hot alkali metals react very vigorously, forming white smoke of their oxides
Very reactive as they only have to lose one electron to have a full outer shell. They form a positive + metal ion and always from ionic compounds.
Melt and boil at relatively low temperatures for metals. The melting and boiling points of the metal decrease going down the group
Reaction with water
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Lithium, sodium and potassium float on the water and moves whilst fizzing
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Hydroxides of all alkali metals are soluble in water, which has a high pH.
Other reactions
React vigorously with non-metals such as chlorine gas. Produce metal chlorides, which are white solids. Metal chlorides all dissolve readily in water to form a colourless solution.
React quickly with group 7 atoms as they both only need to lose/gain a single electron to both have a full outer shell.
Electronic structures
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Metals and non-metals
Properties
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Metals are malleable and ductile, whereas non-metals are brittle.
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Atoms in groups 5,6 and 7 gain electrons to form negative ions. But, atoms in group 1,2 and 3 lose electrons to form positive ions.
Group 0 - Noble gases
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Trends
Boiling points of the noble gases get higher going down the group. EG. Helium = -269C, Radon = -62C
Transition elements
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Physical properties
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High melting and boiling points (exception of mercury, which is liquid at room temperature)
Chemical properties
Much less reactive than the metals in group 1. Therefore, they don't reactive as readily with oxygen, chlorine or water.
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Iron reacts much slower with chlorine than sodium - chlorine has to be passed over iron and heated very strongly for it to react and form red iron chloride.
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Very useful in structural materials as if they corrode, they do so very slowly. However, if the main structural metal is iron (in steel) and it rusts, it will weaken the structure.
Compounds
Copper sulfate is blue, nickel carbonate is pale green, chromium oxide is dark green, manganese chloride is pale pink.
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This is because transition elements can form more than one ion -> compounds of these are different colours.
Very important in the chemical industry as catalysts. EG. nickel for the manufacturing of margerine.
Development
John Dalton
Arranged elements in order of their atomic weights, which had been measured in various chemical reactions.
1808, published in A New System of Chemical Philosophy
John Newlands
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Arranged the elements in order of atomic weight but noticed that every eighth element was similar in property.
However, he assumed that every element had been found and didn't take into consideration that chemists were still discovering new ones. He didn't leave gaps in his table and so the pattern broke down after calcium.
Dmitri Mendeleev
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Placed them in order of their atomic weights but arranged them so that regularly occurring patterns in their properties could be seen.
He left gaps for elements that hadn't been discovered and then used his table to predict what their properties should be.
Years later, when more elements had been discovered, it was shown that not all elements fit his pattern. EG. ARGON. Its relative atomic mass was higher than potassium but if it was before, then it would be in the same group as reactive metals.
This problem was solved when, during the 20th century and scientists had found more about the structure of the atom, the periodic table was arranged in order of its atomic number.
Group 7 - halogens
Properties
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Low melting and boiling points, which increase going down the group. EG. FLUORINE = mp = -220C, bp = -188C
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All exist as molecules made up of pairs of atoms - diatomic molecules. Joined together by a covalent bond
Reactions
Electronic structure affects how they react - all have 7 electrons in their outer shell so they only have to gain one more electron to become stable.
When they react with a non-metal, they gain an extra electron by sharing a pair of electrons with another atom, eg. hydrogen.
Reaction with Hydrogen
FLUORINE = explosive, even at -220C in the dark.
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IODINE = only at over 300C with a platinum catalyst (very slow, reversible)
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When they react with metals, they gain a single electron to become stable. EG. sodium chloride, iron bromide
Displacement reactions
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You use solutions of the halogens and their salts in water, eg. chlorine dissolved in water, mixed with potassium bromide. The colour of the solution will be due to the less reactive of the pair of halogens, which is left in the solution as the aqueous molecule. EG. Cl2 will be very pale green, Br2 will be yellow and I2 will be dark red/brown.
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Explaining trends
Trend in Group 7
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Their atoms gain one more electron in their outer shell but the electrostatic force gets weaker. Therefore, it's harder to attract and gain an extra incoming electron.
More shielding, reducing the electrostatic attraction for oncoming electrons.
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Within groups
As you go down a group, the number of shells occupied by electrons increases. This means the atoms become larger down the group.
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This happens because the outer electrons are further away from the attractive force of the nucleus: positive attracts negative
Also, the inner shells 'shield' the outer electrons from the positive charge so there is less electrostatic force.
Trend in Group 1
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This is because the atoms get larger and therefore the electrostatic attraction between the outer electrons and the protons is weaker.
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There''s more shielding affect, reducing the attraction.