Why do the properties of elements change in regular pattern across a period?
The elements on the left side of a period tends to form more ionic bonds, while those on the right side form more covalent bonds.
The atomic radius decreases along a period. As you go across a period, electrons are added to the same energy level. Hence the force with which the nucleus pulls the electrons increases, resulting in smaller atomic radii.
Metallic character decreases along a period.
As you move across a period, first ionization energy increases.As you move across a period, the atomic radius decreases, that is, the atom is smaller. The outer electrons are closer to the nucleus and more strongly attracted to the center. Therefore, it becomes more difficult to remove the outermost electron.
As you move to the right across a period of elements, electronegativity increases.