* Electronegativity: Electronegativity, the ability of an atom to attract electrons, increases as you move across a period. This is because the number of protons in the nucleus increases, leading to a stronger attraction for electrons.

* Effective nuclear charge: The effective nuclear charge, the net positive charge experienced by valence electrons, also increases as you move across a period. This is due to the increasing number of protons and the shielding effect of inner electrons remaining relatively constant.

* Electron Affinity: Electron affinity, the change in energy when an electron is added to a neutral atom, also tends to increase across a period.

These factors mean that atoms on the right side of the periodic table (nonmetals) have a higher tendency to gain electrons and form anions.

Example:

* Sodium (Na): Sodium has a low electronegativity and readily loses its valence electron to form a +1 cation (Na+).

* Chlorine (Cl): Chlorine has a high electronegativity and readily gains an electron to form a -1 anion (Cl-).

Exceptions:

While the general trend is for anionic charge to increase across a period, there are exceptions. For example, some elements, like noble gases, are very stable and do not readily form anions.

Note:

The term "anion" refers to any negatively charged ion, regardless of its charge. The specific charge of an anion depends on the element and the number of electrons it gains.