What Are Constituent Atoms?
- Atoms have three primary constituent particles: electrons, protons and neutrons. Electrons have a negative electrical charge, and exist in the space surrounding the nucleus (center) of an atom. They have a mass of 9.1x10^-28 g, and are represented by the symbol "e-." Protons have a positive charge, and reside in the atom's nucleus. A proton is 1,836 times heavier than an electron, and is represented by "p+." Neutrons have no charge, and reside in the nucleus together with protons. Neutrons weigh about the same as protons, and are designated by the letter "n."
- Normally, atoms of a single element contain the same number of electrons, protons and neutrons. In some cases, however, an atom will have a different number of neutrons, which changes its atomic mass. This type of atom is called an "isotope." These atoms retain their elemental name, but also have a number that indicates their atomic mass. For example, carbon-13 and carbon-14 are isotopes of carbon.
- Individual atoms can be constituents of larger structures known as molecules and compounds, which form when two or more atoms bond to each other. Simple examples of molecules include water (H2O), carbon dioxide (CO2), methane gas (CH4), molecular oxygen (O2) and molecular nitrogen (N2). A compound is any molecule that consists of more than one element. For instance, hydrogen gas (H2) and molecular oxygen (O2) are not compounds, but water (H2O) is.
- Chemical bonds hold constituent atoms together in molecules and compounds. In covalent bonding, two atoms share electrons. In the case of molecular hydrogen (H2), each of two hydrogen atoms has one electron, and both atoms share them. By contrast, ionic bonds form when one atom donates an electron to another atom. One example is the bonding of sodium and chlorine to form sodium chloride (NaCl). In this case, the sodium atom donates an electron to the chlorine. They subsequently gain opposing electrical charges, which bonds them together.
