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The Modern Periodic Table
At first, not all scientists thought the periodic table was important.
Why?
-Just thought it was `fun'
-Not much evidence to suggest elements really fit together like this.
What changed their opinion?
-After M. Left his work, the newly discovered elements fit into the gap.
-Convincing evidence.
-As more evidence came, realised it was a useful tool for predicting properties, it really worked.
-19th century, discovered electronic structure, matched up very well.
-Now they accepted the importance.
Modern Periodic Table, based on electronic structure
-Use electronic structure to predict chemical properties.
-Electrons in atoms, shells, correspond to energy levels.
-Apart from transition metals, metals in the same group have the same number of
electron in their outer shells.
-Group number= the number of electrons in the outer shell.
-The positive charge of the nucleus attracts the negative charge of the electrons, holds
them together, the further away from the nucleus, the less the attraction.
Shielding: the more the inner the electrons, the more they block the charge of the
nucleus.
Increased distance & shielding, less attraction, electron more easily lost. Reason why
G1 metals more reactive as you go down.
Also means harder to gain an electrons, reason why G7 elements are more reactive as
you go up…read more

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Group 1 ­ The Alkali Metals
More reactive as FORM IONIC COMPOUNDS WITH NON-
you go down. METALS.
Trends, AS YOU GO -Keen to lose their outer electron to form
DOWN: a 1+ ion.
-More reactive, as -No way they'd consider bonding
covalently.
more shells shielding
-Always form ionic compounds, and
+ve charge of produce white compounds, which
nucleus, therefore dissolve in water to produce colourless
easier to escape. liquids.
-Have lower melting & Reaction With Water Produces
boiling points. Hydrogen.
-When Li, Na, K put in water, react
These metals have vigorously.
low densities. -Float and move around the
surface- Fizz furiously.
-Produce hydrogen, K gets hot
enough to ignite it.
-Form hydroxides, dissolve in
water to produce alkaline
solutions.…read more

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Group 7 ­ The Halogens
-LESS REACTIVE as Halogens: non-metals with
you go down. coloured vapours.
-More shells, Fluorine, very reactive poisonous
therefore less yellow gas.
attraction to the Chlorine, fairly reactive
nucleus, therefore poisonous dense green gas.
harder to gain Bromine, a dense poisonous red-
electron. brown volatile liquid.
-HIGHER MELTING Iodine, dark grey crystalline
& BOLING POINTS solid/purple vapour.
AS YOU GO DOWN. ALL EXIST AS PAIRS OF
ATOMS.
More reactive Halogens
displace less reactive ones.
Halogens form ionic More reactive halogens will
bonds w/ metals. displace less reactive ones in
-Form halides w/ 1- an aqueous solution of its salt.
E.g. Chlorine can displace
charge when they bond
Bromine from an aqueous sol
w/ metals. of its salt.…read more

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Transition Elements
Transition Elements Have more than one ion
-Are typical metals that have the (variable oxidation states)
E.g. Fe can be 2+ or 3+, Cu
properties of proper metals.
­ 1+ or 2+ and Cr 2+ or 3+.
-Good conductors of heat + Different ions form different
electricity. coloured compounds, e.g.
-Dense, strong, Shiny Fe2+ is green, Fe3+ is
-Much less reactive than alkali red/brown (rust)
metals, don't react vigorously with
water or oxygen.
-Much denser, stronger + harder
than G1 metals and have
HIGHER MELTING points (except
mercury)
Compounds are very colourful# Transition Metals & their
compounds make good
-The compounds are colourful due to the catalysts.
transition metal
-Potassium Chromate (VI) Yellow Iron-Catalyst in the Haber Process
-Potassium Mangnate (VIII) Purple in making Ammonia.
-Copper (II) Sulfate Blue Manganese (IV) Oxide-Good
-Colours in gemstones e.g. Sapphires blue catalyst in the decomposition of
b/c transition metal. Hydrogen Peroxide.
Nickel-Useful in Hydrogenation.…read more

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Hardness of Water
Hard water: scum & scale. Temporary Hardness Permanent Hardness
Caused by the hydocarbonate ion Caused by dissolved calcium sulfate.
HCO3- in Ca(HCO3)2.
-Soft water; nice lather.
-Hard water- nasty scum (unless Removed by boiling, decomposes The method of boiling DOES NOT
using soapless detergent). into CaCO3: insoluble lime scale. WORK on permanent hardness.
-Problem: calcium + magnesium
ions reacting w/ soap to make
scum, therefore A LOT of soap Can also be softened by adding Can be softened by adding Na2CO3,
Na2CO3, carbonate ions react with carbonate ions react with Ca 2+ and
needed to make a decent lather. Ca 2+ and Mg 2+ to produce an Mg 2+ to produce an insoluble
HARD WATER- when heated insoluble precipitate. precipitate.
forms furring/scale (calcium Can also be removed through ion Can also be removed through ion
carbonate) on insides of pipes, exchange columns, lots of sodium exchange columns, lots of sodium
kettles etc. In boilers, reduces ions exchange for Ca2+ and Mg2+ ions exchange for Ca2+ and Mg2+
ones. ones.
efficiency of heating pipes,
replaced-> MONEY.
Scale, also a thermal insulator, Hardness cause by mineral ions
takes longer for kettle to boil.
-Contain a lot of Ca2+ and Mg2+ ions.
-Caused by rain falling on rocks and compounds containing ions
dissolving into it.
NOT ALL BAD: Ca2+ ions good for healthy teeth & bones.
-Those who drink hard water less likely to get heart disease.…read more

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