Final answer:
As one moves from left to right across a row on the periodic table, the number of electrons increases by one for each subsequent element, leading to a higher nuclear charge, which in turn causes the atomic radius to decrease and increases both ionization energy and electronegativity.
Step-by-step explanation:
The number of electrons in an atom changes as you move across a row in the periodic table. Starting with hydrogen (Z=1), each subsequent element to the right has one additional proton and one additional electron. This increase in electrons and protons results in a greater nuclear charge, leading to a tighter attraction between the nucleus and the valence electrons.
Hence, the atomic radius decreases from left to right across a row. When moving across certain rows, such as from lithium (Li) to neon (Ne), each element has the same number of electron shells, but the number of electrons in the outermost shell increases sequentially until the shell is filled.
Additionally, the periodic trend of ionization energy shows that it generally increases across a row because the valence electrons are held more tightly due to the increased nuclear charge, and so more energy is required to remove them. Similarly, the periodic trend of electronegativity increases across a row as the atomic size decreases and the nucleus exerts a stronger pull on the bonding electrons.