Metals, Nonmetals, and Metalloids
Metals, nonmetals and metalloids are the three main classes of elements: metals are shiny, malleable conductors of heat and electricity, nonmetals are mostly dull, brittle insulators, and metalloids have properties between the two. In brief: copper is a metal, sulfur is a nonmetal and silicon is a metalloid, and in the periodic table metals lie mostly on the left, nonmetals on the right and metalloids along a zigzag line between them.
The three classes are a convenient way of organizing the 118 elements and predicting their behavior. Roughly three quarters of the elements are metals. This article describes the properties of each class, shows their location in the periodic table, compares them in a table, includes a density calculation for identifying a metal, and explains why the borderline between the classes is not sharp.
What are metals?
Metals are elements whose atoms tend to lose electrons easily to form positive ions. In a piece of metal, the outer electrons move freely through a lattice of positive ions, which explains the typical physical properties.
- Luster: a shiny surface when freshly cut or polished.
- Malleability and ductility: they can be hammered into sheets and drawn into wires.
- Conductivity: they conduct heat and electricity well.
- State: solid at room temperature, except for mercury, which is a liquid.
- High density and melting point: true for many, but sodium and potassium are soft with low melting points, and they float on water.
What are nonmetals?
Nonmetals tend to gain or share electrons. They have a wide variety of forms: gases (hydrogen, oxygen, nitrogen, chlorine and the noble gases), one liquid (bromine) and solids (carbon, sulfur, phosphorus and iodine). Typical properties are:
- dull surface when solid;
- brittle: solid nonmetals shatter when hit;
- poor conductors of heat and electricity (graphite, a form of carbon, is an exception for electricity);
- lower density and lower melting points than most metals.
What are metalloids?
Metalloids, also called semimetals, have a mix of metallic and nonmetallic properties. The elements most often listed are boron, silicon, germanium, arsenic, antimony and tellurium. Silicon, for example, has a shiny, metal-like surface but is brittle, and it is a semiconductor, which means its conductivity lies between that of a conductor and an insulator and can be controlled. This property makes silicon and germanium the basis of electronics.
Metals, nonmetals and metalloids compared
| Property | Metals | Nonmetals | Metalloids |
|---|---|---|---|
| Appearance | Shiny | Dull | Often shiny |
| Malleable? | Yes | No, brittle | No, brittle |
| Electrical conduction | Good | Poor | Semiconductor |
| Heat conduction | Good | Poor | Moderate |
| Typical ion formed | Positive (cation) | Negative (anion), or shares electrons | Varies |
| Examples | Fe, Cu, Al, Na | O, S, C, Cl | Si, Ge, As, B |
Where are they in the periodic table?
Metals occupy the large left and center part of the periodic table, including the alkali metals, alkaline earth metals, transition metals and the metals below the zigzag line. Nonmetals sit in the upper right corner, along with hydrogen at the top left. The metalloids lie along a stair-step line that separates metals from nonmetals, running from boron down to tellurium, and sometimes astatine.
Worked example: identifying an element
A student has four samples. Use the observations to classify each and, for the first, to identify it by density.
| Sample | Appearance | Hit with a hammer | Conducts electricity? | Class |
|---|---|---|---|---|
| A | Yellow, shiny | Flattens | Yes | Metal |
| B | Pale yellow powder | Crumbles | No | Nonmetal |
| C | Gray, shiny | Shatters | Weakly | Metalloid |
| D | Red-brown, shiny | Flattens, bends | Yes, very well | Metal |
- Sample A. A rectangular bar measures 4.0 cm × 2.5 cm × 1.0 cm. Its volume is 4.0 × 2.5 × 1.0 = 10.0 cm3.
- Density. The bar has a mass of 193 g, so the density is 193 ÷ 10.0 = 19.3 g/cm3.
- Identification. This matches gold, whose density is 19.3 g/cm3. The very high density, together with the yellow color and malleability, supports the identification.
- Sample D. The red-brown color and high electrical conductivity point to copper (density 8.96 g/cm3), and a density measurement would confirm it.
Brass would have a similar color to gold, but its density is about 8.5 g/cm3, so density is a useful test to tell them apart.
What are the exceptions?
- Mercury is a liquid metal at room temperature, and gallium melts in the hand at about 30 °C.
- Sodium and potassium are soft enough to cut with a knife.
- Graphite conducts electricity, though carbon is a nonmetal. Diamond, another form of carbon, is an insulator.
- Bromine is a liquid nonmetal.
- Iodine is a shiny, almost metallic-looking solid, yet it is a nonmetal.
How did the classification develop?
Antoine Lavoisier already divided simple substances into gases, metals, nonmetals and earths in 1789. Later, Jöns Jacob Berzelius arranged elements as electropositive or electronegative. The periodic table of Dmitri Mendeleev in 1869 grouped elements in a way that showed the pattern of the transition from metals to nonmetals across each period. The category of metalloids became established in the 20th century with the growth of semiconductor technology. The transistor, invented in 1947 at Bell Labs, was first made from germanium.
Which mistakes are common?
Mistake 1: Treating the classes as sharp categories
The change from metal to nonmetal is gradual, and some elements are classified differently by different sources.
Mistake 2: Assuming that all metals are hard and heavy
Lithium is lighter than water, and sodium can be cut with a knife.
Mistake 3: Saying that all nonmetals are gases
Carbon, sulfur and phosphorus are solids, and bromine is a liquid.
Mistake 4: Thinking that metalloids are a mixture of a metal and a nonmetal
Metalloids are single elements with intermediate properties.