SC6: groups in the periodic table Flashcards
what are group 1 elements called?
alkali metals
physical properties of alkali metals
-shiny
-soft (can be cut with a knife)
-low melting points
-low density (some can float on water)
melting points _____ as you go down the alkali metals
decrease
reactivity _____ as you go down the alkali metals
increases
why do all the alkali metals have similar chemical properties
atoms of group 1 elements all have one electron in their outer shell
what do the alkali metals react with water to produce?
a metal hydroxide and hydrogen
lithium and water
fizzes steadily, slowly becomes smaller until it disappears
sodium and water
melts to form a ball, fizzes rapidly, quickly becomes smaller until it disappears
potassium and water
quickly melts to form a ball, burns violently with sparks and a lilac flame, disappears rapidly, often with a small explosion
what happens when a group one element takes part in a reaction
its atoms lose their outer electron and form cations
what do cations have to do with the reactivity of group 1 metals?
the more easily cations form, the more reactive the metal
why does reactivity of group 1 metals increase as you go down the group
-the atoms become larger
-the outer electron becomes further from the nucleus
-the force of attraction between the nucleus and the outer electron decreases
-the outer electron is lost more easily
what are halogens?
-simple molecules
-each molecule contains two halogen atoms joined by a single covalent bond
the colour and physical states of chlorine, bromine and iodine at room temperature:
chlorine:
pale green gas
bromine:
brown liquid
iodine:
purple-black solid
melting and boiling points _______ going down group 7
increase
why do the melting points and boiling points of the halogens increase going down group 7
-the molecules become larger
-the intermolecular forces become stronger
-more energy is needed to overcome these forces
why do halogens all have similar chemical properties?
they all have seven electrons on their outer shells
halogen + metal
salt
halogens become _____ reactive going down group 7
less
reactions with fluorine and iron wool (+colour)
cold iron wool burns to produce white iron(III) fluoride
reactions with chlorine and iron wool (+colour)
hot iron wool burns vigorously to produce orange-brown iron(III) chloride
reactions with bromine and iron wool (+colour)
hot iron wool burns quickly to produce red-brown iron(III) bromide
reactions with iodine and iron wool (+colour)
hot iron wool reacts slowly in iodine vapour to produce grey iron(II) iodide
hydrogen + halogen
hydrogen halide
what are hydrogen halides at room temperature?
gases
what do hydrogen halides produce when they dissolve in water?
acidic solutions
fluorine’s reaction with hydrogen
explodes in the cold and dark, forming hydrogen fluoride
chloride’s reaction with hydrogen
explodes with a flame in sunlight, forming hydrogen chloride
bromine’s reaction with hydrogen
vigorous reaction with burning hydrogen, forming hydrogen bromide
iodine’s reaction with hydrogen
very slow reaction when heated strongly, forming some hydrogen iodide
test for chlorine
-damp litmus paper is bleached white when it is placed in chlorine
-if damp blue litmus paper is used, the paper turns red then white
why are halogens less reactive as you go down the group?
-with group 7 elements, an electron must be gained
-electrons are attracted to the nucleus, therefore if there is a short distance between the outer shell and the nucleus, electrons will have a stronger attraction to the nucleus
-as you go down the group, shells increase and it is harder for the nuclei to attract electrons
halogen displacement reaction
a more reactive halogen can displace a less reactive halogen from solutions of its salts
boiling points of noble gases
-low
-increase as you go down the group
why do boiling points of noble gases increase as you go down the group?
-the atoms become larger
-the intermolecular forces between the atoms become stronger
more energy is needed to overcome these forces
densities of noble gases
-particles in gases are widely spaced, so the noble gases have low densities
-density increases going down the group
are the noble gases reactive?
no, they’re inert
why are noble gases inert?
-when elements react, their atoms complete their outer shells by losing, gaining, or sharing electrons
-the atoms of noble gases already have complete outer shells, so they have no tendency to lose, gain, or share electrons
helium
-used as a lifting gas in party balloons and airships
helium is:
-less dense than air, so balloons and airships rise
-non-flammable so the helium cannot set on fire
argon
-used as a ‘shield gas’ when welding pieces of metal together
argon is:
-denser than air, so it stops air getting to the metal
-inert, so the hot metal cannot oxidise and spoil the weld
why are noble gases used in filament lamps? (lamps that become very hot and glow brightly when an electric current is passed through them)
-the hot metal wires will burn away if any oxygen from air is present in the lamp
-argon, krypton and xenon are very unreactive
-they replace the air inside the lamp, preventing the metal wire from burning away
