The periodic table may seem to be just a simple list of discovered elements but there are many trends within the table that allow one to easily conceptualize and understand the properties that effect the differing elements.
Atoms are simply the smallest pieces of matter that inherently share the properties of their respective design or element. The size of an atom depends upon how far away it’s valence, or outermost, electrons are from the nucleus of the atom. If the distance from the valence electrons to the nucleus is ‘large’ then the size of the atom is also ‘large’, so there exists a direct relationship between the size of an atom and the distance between the nucleus and the outermost electrons. The atomic size of elements increases when moving down the periodic table, and decreases when moving to the right. Moving downwards yields increases in atomic size as the number of shielding electrons and nuclear charge increase proportionally, but the energy levels increase causing the valence electrons to subsequently spread farther out into more distant energy levels, resulting in an increase in atomic size. When moving to the right there is an increase in nuclear charge, with energy levels remaining constant, causing the electrons to get pulled rather strongly outwards resulting in a decrease of atomic size.
Ionization energy is defined as the amount of energy necessary to fully release or remove the outermost electron from a lone atom. The process of ionization has a positive ion as it’s byproduct. Many things have to be taken into account when determining the ionization energy of an element, as it can depend upon the shielding electrons, nuclear charge, and the energy levels present within the element. Moving across the periodic table yields a general increase in ionization energy as the deciding factor, the nuclear energy, increases thus making it more difficult to dislodge the outermost electron thus requiring more energy. Moving down the table the energy levels become the deciding factor as the farther the electrons move from the nucleus(larger energy levels), the smaller the amount of energy becomes to remove that one electron. Moving downwards, the nuclear charge and the shielding electrons generally cancel each other, resulting in the energy levels becoming the determining factor of the ionization energy. There are however fluctuations in these trends as each element has many different properties that cause greater slightly larger or smaller ionization energies, but they generally follow the same trend on the periodic table as the atomic size of the elements.