Electronic Repulsion - If the electronic density decreases, the ionization energy with increase and vice versa. If an electron gets released, it decreases the electronic repulsion. This makes releasing another electron harder than the first on unless the electron that is being released comes from another energetic level.
# Of Energy Levels - The more energy cores that get filled up, the more ionization levels decrease. When we see the energy levels go from top to bottom, the ionization also go from most to least. This is why ionization occurs on the highest level.
Nuclear Charge - The higher the atomic number, the higher charge in the nuclei. This also makes the ionization energy higher as it increases from left to right of in other words, if the nuclear charge gets higer, the energy gets higher as well.
Factors that determine atomic volume:
How many protons are in the nucleus (nuclear charge)
How many energy levels carry electrons (electrons in outer energy level)
