Describe and explain the trends for effective nuclear charge, atomic radius, ionic radius, and ionization energy across a period and down a group.

The trends for each of the atomic properties given above are as follows:
1. EFFECTIVE NUCLEAR CHARGE:The nuclear charge refers to the total charge of all the protons in the nucleus of an atom. The effective nuclear charge refers to all the net positive charge that is experienced by an electron in an atom that has many electrons. The effective nuclear charge increases across a period and decreases down a group.
2. ATOMIC RADIUS: This refers to the measured distance between two nuclei, that is, it is a measure of the size of an atom. The atomic radius of an element typically increases with increase in the period number and decreased as one moves from left to right in a period. This is because, as the number of the period increases, the number of atomic shells increase and so also the atomic size.
IONIC RADIUS: This refers to the radius of an atom's ions in ionic crystal structure. Remember that an ion is an atom that has gained or lose electron[s]. Generally, ionic radius increases as on moves from the top to the bottom of the periodic table and it decreases as one moves across the periodic table from left to right.
4. IONIZATION ENERGY: This is the energy that is needed to compleetely remove an electron from a gasous atom or ion. The value of ionization energy is always positive. Typically, ionization energy increases as one move from left to right across a period and also increases as one go up a group.