Elements are the building blocks of all matter in the known universe. To date, we have identified 92 naturally occurring elements, and we have used technology to synthesize another 20. These elements exist in the atmosphere, hydrosphere, lithosphere, and/or biosphere. Together they form the molecules that make up living and non-living material, drive chemical interactions, and provide the basis of all of the natural resources on the planet Earth.
The periodic table (Figure 8) organizes the elements into groups and reveals patterns in their properties. In the periodic table depicted in Figure 8, the elements known as metals are shaded in light green-gray and those that are nonmetals are orange; those that have properties of both metals and nonmetals are called metalloids and are highlighted in dark green.
The smallest unit of any element is called an atom. The number of protons, neutrons and electrons each type of atom has is what gives each element its unique properties, and determines how it will chemically interact with other elements. They also determine where each element is placed on the periodic table. The first 92 elements listed on the periodic table are present on Earth in varying abundances. Many of these elements have properties that make them conducive to supporting life, producing useful materials, or providing energy. Not all 92 elements are required for the metabolism of living organisms. In fact, only 21 elements are essential to the various forms of life on Earth (Figure 9).
Learn more about building blocks of matter.
Some of these essential elements are required in large amounts and serve as the major building blocks of life. These elements, termed macronutrients, include carbon (C), hydrogen (H+), and oxygen (O2-), and are the elements required in the greatest amounts. Over 93% of plant and animal biomass is made of these three elements. Other macronutrients include nitrogen (N3-), phosphorus (P3-), potassium (K+), sulfur (S2-), calcium (Ca2+), iron (Fe2+), and magnesium (Mg2+). These are required by all forms of life, but in smaller amounts than C, H and O.
Micronutrients or trace nutrients are also essential, but are only required in very small amounts. They generally serve as co-factors, or molecules that assist in chemical reactions. Among the micronutrients are copper (Cu2+), zinc (Zn2+), molybdenum (Mo), boron (B), sodium (Na+), nickel (Ni) and chloride (Cl–).
Under Earth’s atmospheric conditions many elements are found in a form that has an elecrtic charge and are called ions. Ions are electrically charged because they don’t have an equal number of protons and electrons. If an atom has the same number of electrons as protons, the negatively charged electrons cancel out the positively charged protons and the atom’s charge will be neutral. If an atom has more electrons than protons, it will have an overall negative and is called an anion. A cation has more protons than electrons, giving it a positive charge. The electrical charges that ions possess make it possible for an element to form chemical bonds with other elements. Chemically combined elements form compounds, such as water (H2O, two hydrogen [H] atoms combined with one oxygen [O] atom), table salt (NaCl), and carbon dioxide (CO2). This tendency to bond together and form more complex molecules has led to the enormous diversity of both living and non-living forms of matter that we find on Earth.
Check out “Atom Hook-Ups“, a short and playful film explaining types of chemical bonds.
Groups of elements share some common properties. For example, one property metals have in common is that they are good conductors of electricity, while nonmetals are poor electrical conductors. Nonmetals tend to be gaseous under Earth’s atmospheric conditions, and are typically ionic and tend to combine together to form molecules. In the example above, two elements, sodium (Na+, a metal cation) and chloride (Cl–, a non-metal anion), will bond to form salt (NaCl, a neutrally charged molecule).
All of the natural resources that humans use are made of the same elements that make up all of the matter in the universe. Most natural resources, such as trees, water, soil, fossil fuels, and animals are made up of many types of elements joined together. Some natural resources, such as iron, copper, silver, and gold, are made of single elements that are found by themselves in nature.
In the next section you will learn how some of the most important elements for life on Earth are made continually available through natural biogeochemical cycles. You will also learn how human development has impacted the balance of these cycles, and what potential impact this has on natural systems.
Questions to Consider
Which elements make up the air you are breathing? What elements are in your favorite food? Would you rather live without gold or without carbon?