Answer: Number of valence electrons determine how fast or easy for an atom to gain stability. Either by gaining electrons or by losing electrons.
Group one and seven elements react fast because they only have one electron to gain or lose.
Step-by-step explanation:
Number of valence electrons tell us the number of electrons an atom will gain or lose in order to attain stability in electron configuration.
All the elements in a particular group will have the same number of valence electrons as follows:
Group one - 1 valence electron
Group two - 2 valence electrons
Group three - 3 valence electrons
Group four - 4 valence electrons
Group five - 3 valence electrons
Group six - 2 valence electrons
Group seven - 1 valence electron
Group eight - 0 valence electron
Some elements are more reactive than the others because of the electron affinity, oxidation state and electronegativity of the atoms
For instance, elements in group 7 are more reactive than others because of their oxidation state and they have very high electronegativity.
Also, group one elements are more reactive because they only have one electron to loose.