State the trends in reactivity of the group 1 and group 7 elements and explain the reasons why.

Elements react by gaining or losing electrons. Elements wants to reach the stable state of having 8 electrons in the outermost ring, so group 1 elements react by losing an electron, since they have only 1 electron in their outermost shell. Group 7 elements however have 7 electrons in their outermost shells, so they react by gaining an electron to form an outermost ring of 8 electrons.

Group 1 elements get more reactive down the group becasue with each step down the group the number of full electron rings increases by 1 and the outermost electron is further away from the positive nucleus. The further away the outermost negative electron is from the positive nucleus, the weaker the force of electrostatic attraction between the two is and the easier it is for the element to react as less energy is required to remove the electron. Group 7 elements are less reactive down the group because the electron shells have a repulsive effect on the reacting electron, which weakens the force of electrostatic attraction between it and the positive nucleus.