Elements within a group have the same number and distribution of valence electrons. This gives them similar properties; however, these properties are not identical. Instead, there are variations of these properties within a group. These are called periodic trends.
While there are many trends in the periodic table, the most common are:
Atomic radius is the distance from the center of an atom to its outermost edge.
Ionization energy is the amount of energy needed to remove an electron from an atom.
Electron affinity is the energy change that occurs when an atom gains an electron to form a negative ion.
Electronegativity is a measurement of an atom's ability to attract electrons.