EVERYTHING FOR CHEM 3!!

Used to be arranged of atomic weight

Newlands- law of octaves, elements with similar properties in group of 8 but elements placed in wrong groups

Mendeleev- left gaps for inknown elements

Now- electronic structure, elements in same group have same amount of electrons in outer shells

Reactivity: more electronic shells = electrons further away from the nucleus = less attracted to nucleus = easily lost = more reactive

have low density

• alkali metal + non-metal = ionic compound (charge +1)
• ionic compound = white solids = dissolve in water = colourless solutions
• colourless solutions + water = hydrogen

down the group:

• more reactive
• lower boiling point
• lower melting point

React with water and oxygen

are coloured vapours

molecules- pair of atoms

halogens + metals = ionic salts (charge -1)

halogens + non-metals = molecular compounds

Down the group:

• less reactive
• higher melting point
• higher boiling ponit

Reactive halogens displace less reactive halogens in aqueous solution

Group 2 & 3- overlap- if theres 2 electrons in the 3rd shell, the 4th shell can hold 18 electrons

Compared to group 1:

• higher melting points
• higher densities
• harder,stronger

More than 1 ion, i.e. Fe2+  Fe3+

with very colourful compounds

Arrhenius: "acids release H+ in water"

but it only worked for acids dissloved in water ammonia gas can act as a base even when it isn't dissolved in water

Lowry & Bronsted: "Acids release H+ ions" - are proton donors                             "Bases accept H+ ions" - proton acceptors

Protons are hydrated in water-

In acidic solutions: Acid molecules dissociate, releasing H+ ions which are surrounded by water molecules. H+ (aq)