Metals Versus Nonmetals - Comparing Properties

Elements may be classified as either metals or nonmetals based on their properties. Much of the time, you can tell an element is a metal simply by looking at its metallic luster, but this isn't the only distinction between these two general groups of elements.

Metals

Most elements are metals. This includes the alkali metals, alkaline earth metals, transition metals, lanthanides, and actinides. On the periodic table, metals are separated from nonmetals by a zig-zag line stepping through carbon, phosphorus, selenium, iodine, and radon. These elements and those to the right of them are nonmetals. Elements just to the left of the line may be termed metalloids or semimetals and have properties intermediate between those of the metals and nonmetals. The physical and chemical properties of the metals and nonmetals may be used to tell them apart.

Metal Physical Properties:

• Lustrous (shiny)
• Good conductors of heat and electricity
• High melting point
• High density (heavy for their size)
• Malleable (can be hammered)
• Ductile (can be drawn into wires)
• Usually solid at room temperature (an exception is mercury)
• Opaque as a thin sheet (can't see through metals)
• Metals are sonorous or make a bell-like sound when struck

Metal Chemical Properties:

• Have 1-3 electrons in the outer shell of each metal atom and lose electrons readily
• Corrode easily (e.g., damaged by oxidation such as tarnish or rust)
• Lose electrons easily
• Form oxides that are basic
• Have lower electronegativities
• Are good reducing agents

Nonmetals

Nonmetals, with the exception of hydrogen, are located on the right side of the periodic table. Elements that are nonmetals are hydrogen, carbon, nitrogen, phosphorus, oxygen, sulfur, selenium, all of the halogens, and the noble gases.

Nonmetal Physical Properties:

• Not lustrous (dull appearance)
• Poor conductors of heat and electricity
• Nonductile solids
• Brittle solids
• May be solids, liquids or gases at room temperature
• Transparent as a thin sheet
• Nonmetals are not sonorous

Nonmetal Chemical Properties:

• Usually have 4-8 electrons in their outer shell
• Readily gain or share valence electrons
• Form oxides that are acidic
• Have higher electronegativities
• Are good oxidizing agents

Both metals and nonmetals take different forms (allotropes), which have different appearances and properties from each other. For example, graphite and diamond are two allotropes of the nonmetal carbon, while ferrite and austenite are two allotropes of iron. While nonmetals may have an allotrope that appears metallic, all of the allotropes of metals look like what we think of as a metal (lustrous, shiny).

The Metalloids

The distinction between metals and nonmetals is somewhat fuzzy. Elements with properties of both metals and nonmetals are called semimetals or metalloids. A stair-step line roughly divides metals from nonmetals on the periodic table. But, chemists recognize that naming one element a "metal" and the one next to it a "metalloid" is a judgement call. In truth, most metals display the properties of nonmetals under certain conditions, and nonmetals act like metals in some situations.

Hydrogen is a good example of an element that acts as a nonmetal some times, but as a metal other times. Under normal conditions, hydrogen is a gas. As such, it acts like a nonmetal. But, under high pressure it becomes a solid metal. Even as a gas, hydrogen often forms the +1 cation (a metallic property). Yet, sometimes it forms the -1 anion (a nonmetal property).

Sources

• Ball, P. (2004). The Elements: A Very Short Introduction. Oxford University Press. ISBN 978-0-19-284099-8.
• Cox, P. A. (1997). The elements: Their origin, abundance and distribution. Oxford University Press, Oxford. ISBN 978-0-19-855298-7.
• Emsley, J. (1971). The inorganic chemistry of the non-metals. Methuen Educational, London. ISBN 0423861204.
• Gray, T. (2009). The Elements: A Visual Exploration of Every Known Atom in the Universe. Black Dog & Leventhal Publishers Inc. ISBN 978-1-57912-814-2.
• Steudel, R. (1977). Chemistry of the non-metals: with an introduction to atomic structure and chemical bonding. English edition by FC Nachod & JJ Zuckerman, Berlin, Walter de Gruyter. ISBN 3110048825.