Know the difference between the groups and the periods. The columns of the periodic table are referred to as groups and the rows of the periodic table are referred to as periods. Depending on whether you are examining a row or a period, you will find different shifts in trends.
Examine how atomic radius is displayed on the periodic table. As you move down a group, the atomic radius increases because the the number of protons and the number of energy levels for electrons increases. Since the electrons in the outer shell, or the valence electrons, of atoms with a larger amount of energy levels are not as affected by the positive charge of the protons, the atomic radius increases. When you go from the left to the right across a row, the atomic radius decreases because the electrons are in the same energy levels, yet more protons are being added to the nucleus, which pulls them in tighter.
Analyze the electronegativity patterns. The electronegativity is how well the atom is able to attract the electrons of another atom during chemical bonding. As you move down a group, the electronegativity decreases. This is mainly because the radius is larger and losing an electron does not take much energy. As you move across a period from left to right, the electronegativity generally increases because the size of the radius is smaller and there is a greater number of valence electrons.
Examine the pattern associated with the ionization energy. The ionization energy is the amount of energy the atom needs to lose an electron. As you move down a group, the ionization energy decreases because the number of energy levels is larger, which helps to shield the electrons from the positive charge of the protons. As you go across a period from left to right, the ionization energy increases because there is no increase in shielding affect across a period, so the electrons are being held tighter to the protons.
Determine how the elements in group 18 are different from the others. The elements in group 18 are the noble gases. They have a complete octet, so they are less likely to want to lose or attract electrons. Helium, neon, and argon generally are not associated with electronegativity values. However, the electronegativities for krypton, xenon and radon are larger than those of group 17.