<P> 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 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 . Going down a main group, the effect of increasing nuclear charge is generally outweighed by the effect of additional electrons being further away from the nucleus . Atoms generally become larger, ionization energy falls, and metallic character increases . The net effect is that the location of the metal--nonmetal transition zone shifts to the right in going down a group, and analogous diagonal similarities are seen elsewhere in the periodic table, as noted . </P> <P> Depictions of metalloids vary according to the author . Some do not classify elements bordering the metal--nonmetal dividing line as metalloids, noting that a binary classification can facilitate the establishment of rules for determining bond types between metals and nonmetals . Metalloids are variously grouped with metals, regarded as nonmetals or treated as a sub-category of nonmetals . Other authors have suggested that classifying some elements as metalloids "emphasizes that properties change gradually rather than abruptly as one moves across or down the periodic table". Some periodic tables distinguish elements that are metalloids and display no formal dividing line between metals and nonmetals . Metalloids are shown as occurring in a diagonal band or diffuse region . </P> <P> Metalloids usually look like metals but behave largely like nonmetals . Physically, they are shiny, brittle solids with intermediate to relatively good electrical conductivity and the electronic band structure of a semimetal or semiconductor . Chemically, they mostly behave as (weak) nonmetals, have intermediate ionization energies and electronegativity values, and amphoteric or weakly acidic oxides . They can form alloys with metals . Most of their other physical and chemical properties are intermediate in nature . </P> <P> Characteristic properties of metals, metalloids and nonmetals are summarized in the table . Physical properties are listed in order of ease of determination; chemical properties run from general to specific, and then to descriptive . </P>

What are the general properties of a metalloid
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