The additional pull on outer electrons as nuclear charge increases generally outweighs the screening effect of having more electrons.

With some irregularities, atoms therefore become smaller, ionization energy increases, and there is a gradual change in character, across a period, from strongly metallic, to weakly metallic, to weakly nonmetallic, to strongly nonmetallic elements.

A related effect can be seen in other diagonal similarities between some elements and their lower right neighbours, specifically lithium-magnesium, beryllium-aluminium, and boron-silicon.

They also said that metalloids are typically semiconductors, though antimony and arsenic (semimetals from a physics perspective) have electrical conductivities approaching those of metals.

Selenium and polonium are suspected as not in this scheme, while astatine's status is uncertain.

Typical metalloids have a metallic appearance, but they are brittle and only fair conductors of electricity. Metalloids are usually too brittle to have any structural uses.

They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.

This exception arises due to competing horizontal and vertical trends in the nuclear charge.

Going along a period, the nuclear charge increases with atomic number as do the number of electrons.The electrical properties of silicon and germanium enabled the establishment of the semiconductor industry in the 1950s and the development of solid-state electronics from the early 1960s.The term metalloid originally referred to nonmetals.You might not realise it, but sending even a short email has an impact on the environment.Scientists estimate that an email adds about four grams (0.14 ounces) of carbon dioxide equivalent into the atmosphere.listed twelve (Emsley's plus boron, carbon, silicon, selenium, bismuth, polonium, moscovium and livermorium).