Attempts to Classify Elements.
1864 - John Newlands tried to arrange 63 known elements into a table, in order of atomic weight. He noticed similarities between every 8th element (law of octaves). He noticed repeated patterns (periodicity) but missing elements caused problems.
1869 - Dimitri Mendeleev arranged elements in table with some gaps for missing elements. He was able to accurately predict properties of these missing elements, which meant his table was accepted.
Today - Modern Periodic table arranged in order of atomic (proton) number (i.e in terms of electronic structure). Groups (columns) of elements have same number electrons in outer shell, so similar properties. Periods (rows) have same number of shells.
Group 1 - Alkali Metals
Lithium (Li), Sodium (Na), Potassium (K).....(Rb...Cs...Fr)
Low melting + boilings points that decrease as you go down group
Low density (Li, Na + K float on water)
More reactive as you go down group (Li < reactive than K). (Outer electron is further away so lost easily.) *((o)) *((((o))))
One electron in outer shell = similar properties.
React vigorously with water and oxygen (must be stored in oil).
Alkali Metal + Water ---> Metal Hydroxide and Hydrogen (Squeeky pop test!)
React with non-metals to form IONIC COMPOUNDS. Become +1 metal ions. Form white soluble solids (i.e Table Salt NaCl)
Group 7 - The Halogens
Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I)...(At)
Melting + Boling points increase as you go down group (fluorine gas, bromine liquid at room temp)
Diatomic Molecules (exist as pairs of atoms)
Less reactive as you go down group (Outer shell is further away, so electrons are not as attracted by influence of nucleus) (F > reactive than l )
*----> ((o)) (((((o))))) <- - *
Produce IONIC SALTS with metals (i.e Table Salt NaCl). Form Halide Ions (-1)
React with non-metals to form molecular compouns (i.e 2HCl).
More reactive halogen will displace less reactive (i.e chlorine will displace bromine and iodine, but NOT fluorine)
Transition Metals (between groups 2 & 3)
Also known as Transition Elements. Examples include Iron (Fe) and Gold (Au)
Form coloured compounds
Have multiple ions with different charges (i.e Fe+2, Fe+3)
Used as catalysts (lower activation energy in reactions) as fairly unreactive
Good conductors of heat and electricity.
Can be bent and hammered (ductile)
(unlike groupd 1 metals) Hard and strong, with high boiling + melting point (except mercury) + High density.
Similar properties due to 3rd energy shell holding up to 18 electrons once 2 are in 4th energy shell.