Group 1 elements are referred to as alkali metals because they form oxides and hydroxides that dissolve in water producing alkaline solutions. They have one electron in their outer shell that they lose by oxidation to form ions; Na Na+ + e- that is more stable (Schwerdtfeger et al. 7520). As one move down the group 1, the elements atom gets larger as the outer shell electron get easily lost and its radius is governed by the number of layers of electrons around a nucleus and the pull of outer electrons feel from the nucleus, therefore group one element get more reactive as one move down. In addition, they have a decreasing electro negativity, melting and boiling points, increasing reactivity and density. The order of reactivity is as follows; group 1: Cs > Rb > K > Na > Li.
The reactivity of group seven elements differs as they move down the periodic table; they miss one electron from their covalence shell thereby being highly volatile and reactive. Group 7 elements have 7 electrons in their outer shells and need a gain of one electron to be stable. Since there are more electrons, the inner shells shield the nuclear charge more effectively and it therefore becomes difficult as one move down the group making them less reactive (Kitchin et al. 10244). The order of reactivity for group 7 is as follows: F > Cl > Br > l > At.
In conclusion therefore, the distance between the nucleus and the outer electrons variation defines the trends of chemical elements behavior. Group 1 and 7 elements have the highest levels of reactivity except hydrogen in group 1 because they are easily lose and gain the single electron to form a stable element.
Kitchin, J. R. et al. “Modification of the Surface Electronic and Chemical Properties of Pt (111) by Subsurface 3d Transition Metals.” The Journal of Chemical Physics 120.21 (2004): 10240–10246. scitation.aip.org. Web. 21 Oct. 2013.
Schwerdtfeger, Peter et al. “Low Valencies and Periodic Trends in Heavy Element Chemistry. A Theoretical Study of Relativistic Effects and Electron Correlation Effects in Group 13 and Period 6 Hydrides and Halides.” Journal of the American Chemical Society 114.19 (1992): 7518–7527. ACS Publications. Web. 21 Oct. 2013.