Hello, my name is Walter Unglaub, and this is, "What two factors determine the atomic radius of an element?" Well there are several factors that determine the atomic size for any given element, but the two most important ones are the nuclear charge, which is given by the number of protons times the charge of a single electron, so this is a positive number, and the number of electron shells, or energy levels in the atom. So, we might ask, how do these independently affect the size of an atom? Well, here we have an atom where we have a nucleus that is comprised of several neutrons and protons for example, and then if this is a neutral atom, we'll have as many electrons orbiting the nucleus as there are protons in the nucleus. So, if we have a larger nuclear charge, meaning this nucleus is larger, there's going to be a stronger electromagnetic attraction between the positively charged protons and the negatively charged electrons. So, the inner electrons will tend to be attracted more towards the nucleus. However, if you have more electrons and more electron shells, then the size of the atom will tend to be larger compared to the effect of having a larger nuclear charge. So depending on the balance of the nuclear charge in the nucleus and the energy levels of the atom, this will determine the different sizes for different elements. My name is Walter Unglaub, and this what two factors determine the atomic radius of an element.