All nonmetallic elements are generally poor conductors of heat and electricity. There are only 17 nonmetallic elements, while more than 75 percent of the known elements are either pure metals or metalloids, which are better conductors of heat and electricity to a varying degree.
Other than being poor conductors, many of the nonmetallic elements share very little else in common. Of the 17 nonmetallic elements, only six of them are solid in their natural state. Most nonmetallic solids are very dull and feel quite light due to their relatively low density. This includes phosphorous, sulfur, selenium and carbon, all of which are usually hard and brittle. Carbon is one exception, as pure carbon can take on two very different forms with different degrees of hardness. One of these is diamond, which is the hardest mineral found in nature. The other form is graphite, which is one of the only nonmetallic substances that is able to conduct electricity.
There are 11 nonmetallic elements that are gases at room temperature, including all of the noble gases, which are technically nonmetallic. Some of the gaseous nonmetallic elements are hydrogen, oxygen, nitrogen and neon. There is also one nonmetallic element that is a liquid at room temperature, bromine.