Elements: Defined by Their Number of Protons


The simplest atoms have only 1 proton in their nuclei, whereas others have more than 100. The number of protons in the nucleus of an atom, called the atomic number, determines its chemical nature. All atoms with the same number of protons have the same chemical and physical properties. Together, a group of the same kind of atoms is called an element. There are about 90 naturally occurring elements and several more that have been synthesized in the laboratory. You are probably familiar with the names of many elements, including carbon, nitrogen, and oxygen. All carbon atoms have six protons, whereas all nitrogen atoms have seven protons, and all oxygen atoms have eight.

Scientists have organized elements so those with similar properties line up in columns, referred to as groups. This arrangement, called the periodic table, is shown in Figure 1.

Figure 1 – Periodic table of the elements

Each element is assigned a one- or two-letter symbol. The atomic numbers and masses for each element are also shown on the periodic table.
Atoms of the naturally occurring elements are the basic building blocks of Earth’s minerals. Most elements join with atoms of other elements to form chemical compounds. Therefore, most minerals are chemical compounds composed of atoms of two or more elements.

These include the minerals quartz (SiO2), halite (NaCl), and calcite (CaCO3). However, a few minerals, such as native (occurring in pure form in nature) copper, diamonds, sulfur, and gold, are made entirely of atoms of only one element (Figure 2).

Figure 2 – Examples of minerals that are composed of a single element

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