2.3 Chemical Properties and Reactions

Chemical Properties and Reactions

Structure of Matter

Elements

An element is a substance in which all the atoms are the same kind. This is the diagram of an atom of one element—carbon. Carbon is an element that makes up part of carbon dioxide gas in the atmosphere. It is the main substance in coal, graphite, and diamonds. It is also found in all living things.

You are probably familiar with other elements. They include metals like gold, copper, and silver. They include nonmetals like silicon, arsenic, and iodine. They include oxygen, nitrogen, helium, and neon, which are gases, and bromine and mercury, which are liquids at temperatures generally found on Earth.

In ancient times, scientists thought there were only four elements: earth, water, fire, and air. Today 114 elements are recognized internationally, and more will be added. Of these, only 98 occur naturally on Earth; the remaining elements have been made in laboratories.

Each element has its own name, chemical symbol, and atomic number. The chemical symbol is an abbreviation that consists of one or more letters. The first letter is always capitalized. For example, C is the chemical symbol for carbon. Ne is the chemical symbol for neon.