Group one metals (alkali metals)

lithium, sodium, potassium

• reactivity increases as you go down the group • melting (and boiling) points decrease as you go down the group • density increases as you go down the group

group one metal + water => metal hydroxide + hydrogen

2Li (s) + 2H2 O (l) => 2LiOH (aq) + H2 (g)

2Na (s) + 2H2O (l) => 2NaOH (aq) + H2 (g)

2K (s) + 2H2O (l) => 2KOH (aq) + H2 (g)

• effervesces due to hydrogen gas production • floats and moves around the surface • disappears after all of metal has dissolved • NOT AN OBSERVATION TO MENTION IN AN EXAM BUT produces a metal hydroxide and alkaline solution

• strong effervescence • ignites (exothermic reaction) • melts and forms a sphere • NOT AN OBSERVATION TO MENTION IN AN EXAM BUT produces a metal hydroxide to make an alkaline solution

• Ignites to a lilac flame • vigorous effervescence due to hydrogen gas production • made a pop sound • moved around on surface and floats • NOT AN OBSERVATION TO MENTION IN AN EXAM BUT produces a metal hydroxide to dissolve into alkaline solution

when they react with water they produce and alkaline solution (as metal hydroxides are produced)

• potassium had a vigorous reaction with water • reactivity of G1 metals increases as you go down the group • so Rb, Cs and Fr would have even more vigorous, explosive, and exothermic reactions that would be dangerous to complete

• reactivity increases as you go down the group • G1 metals all have one electron in their outer shell • as you go down the group, atoms have more electron shells, so they become larger • so the outer electron is increasingly further away from the nucleus • so the attraction between the nucleus and the outer electron becomes weaker • then less energy is needed to remove the outer electron • this makes it easier for the atom to lose the electron and react • therefore, reactivity increases down the group

• the melting points of group 1 metals decrease as you go down the group • group 1 metals are held together by metallic bonding – positive ions in a sea of mobile, delocalised electrons • as you go down the group, atoms get larger and have more electron shells • the metallic bonds become weaker because the positive nucleus is further from the delocalised electrons • this weaker attraction means less energy is needed to break the bonds • therefore, the melting point decreases as you go down the group

• group 1 metals react with oxygen in air to form oxides • lithium tarnishes slowly, forming a thin layer of lithium oxide • sodium tarnishes faster, showing quicker reaction with oxygen • potassium tarnishes even more rapidly and can ignite in moist air • so, we can guess that rubidium and caesium would react very quickly and may catch fire spontaneously • the increasing speed and intensity of these reactions down the group shows reactivity increases as you go down

4M (s) + O2 (g) => 2M2O (s) and the metal oxide is generally a white powder in appearance