Final answer:
The atom with the highest first ionization energy in any given period of the periodic table is typically the atom at the end of the period. This is due to stronger electrostatic interactions between a more positively charged nucleus and valence electrons as atomic size decreases.
Step-by-step explanation:
In the context of the periodic table and ionization energy trends, the atom you would expect to have the highest first ionization energy (I1) in any given period (row) would be the atom at the end of the period (B), due to increased nuclear charge and decreased atomic radii. This causes a stronger electrostatic interaction between the valence electrons and the nucleus, making the electrons more difficult to remove. For example, the element at the bottom left of a rectangle of six elements in the two far-left columns of the periodic table (like Rubidium, Rb) will have the lowest first ionization energy, as it has a larger atomic radius and fewer protons to hold on to the valence electrons compared to elements at the end of the period.
Ionization energies generally increase from left to right across a period. This is due to a smaller atomic size and stronger electrostatic interactions between the more highly charged nucleus and valence electrons. There can be exceptions to these trends due to factors like electron shielding, but generally speaking, the end of the period will exhibit the highest ionization energies.