On moving from left to right in a period of the modern periodic table, the non-metallic character

In the modern periodic table, as we move from left to right the metallic character decreases and the non-metallic character increases. 

This is because there is one more valence electron with each successive element as we proceed from left to right in a period, while the number of shells stays the same. The attraction between nuclei and electrons increases as effective nuclear charge increases. 

As a result, the element's ability to lose electrons decreases, which results in a loss of metallic character. Moving from left to right in a period enhances the non-metallic nature because an element's ability to acquire electrons increases with increases in effective nuclear charge.