groups 1 and 7

Question 1

2:01 understand how the similarities in the reactions of lithium, sodium and potassium with water provide evidence for their recognition as a family of elements

Answer 1

Group 1 metals such as potassium, sodium and lithium, react with water to produce a metal hydroxide and hydrogen.

The observations for the reaction of water with either potassium or sodium or lithium have the following similarities:

fizzing (hydrogen is produced)
metal floats and moves around on the water
metal disappears
In each case a metal hydroxide solution is produced.

These similarities in the reactions provide evidence that the 3 metals are in the same group of the Periodic Table (i.e. have the same number of electrons in their outer shell).

Question 2

2:02 understand how the differences between the reactions of lithium, sodium and potassium with air and water provide evidence for the trend in reactivity in Group 1

Answer 2

metal + water

lithium:
- fizzing (hydrogen gas is released)
- floats and moves around on the water
- disappears

sodium:
- fizzing (hydrogen gas is released)
- floats and moves around on the water
- melts into a silver-coloured ball
- disappears

potassium:
- fizzing (hydrogen gas is released)
- floats and moves around on the water
- catches fire with a LILAC flame
- disappears

When the group 1 metals react with air they oxidise, showing a similar trend in reactivity as we go down the group of the Periodic Table.

Therefore, as we go down group 1 (increasing atomic number), the elements become more reactive

Question 3

2:04 (Triple only) explain the trend in reactivity in Group 1 in terms of electronic configurations

Answer 3

As you go down the group the outer electron lost from the group 1 metal is further from the nucleus therefore the electron is less attracted by the nucleus and therefore more easily lost.

Question 4

2:05 know the colours, physical states (at room temperature) and trends in physical properties of chlorine, bromine and iodine

Answer 4

chlorine:
- green
- gas at room temp

bromine:
- red-brown
- liquid at room temp

idoine:
- grey
- solid at room temp

Question 5

2:06 use knowledge of trends in Group 7 to predict the properties of other halogens

Answer 5

other halogens -

fluorine:
- yellow
- gas at room temp

astatine:
- black
- solid at room temp

Question 6

2:07 understand how displacement reactions involving halogens and halides provide evidence for the trend in reactivity in Group 7

Answer 6

Group 7 elements are called the Halogens. As you go up group 7 (decreasing atomic number), the elements become more reactive.

By reacting a halogen solution with a potassium halide solution and making observations, the order of their reactivity can be deduced:

chlorine + Potassium bromide: colourless to orange
chlorine + Potassium iodide: colourless to brown

bromine + Potassium iodide: colourless to brown

no change for:
potassium chloride + anything
iodine + everything
gaps for other things

From the above results, chlorine displaces both bromine and iodine, and bromine displaces iodine. Therefore the order of reactivity is: chlorine is more reactive than bromine, which in turn is more reactive than iodine.

Question 7

2:08 (Triple only) explain the trend in reactivity in Group 7 in terms of electronic configurations

Answer 7

The higher up we go in group 7 (halogens) of the periodic table, the more reactive the element. The explanation concerns how readily these elements form ions, by attracting a passing electron to fill the outer shell.

In fluorine the outer electron shell is very close to the positively charged nucleus, so the attraction between this nucleus and the negatively charged electrons is very strong. This means fluorine is very reactive indeed.

However, for iodine the outer electron shell is much further from the nucleus so the attraction is weaker. This means iodine is less reactive.