The atom is the basic building block of matter. Atoms combine to form pure elements, compounds, and complex forms like computers and phones. Atoms are the smallest particle of matter than cannot be further subdivided using chemical means. In order to understand how atoms interact with each other, you first need to understand the basic parts of an atom. There are 3 main components of atoms:
- Protons – The number of protons in an atom is often denoted by the letter Z. Each proton carries a positive electrical charge. The number of protons determines the type of atom. For example, an element with 1 proton is hydrogen. One with 2 protons is helium. The number of neutrons and electrons don’t have any bearing on the type of atom. In fact, an atom does not even need neutrons or electrons. The most common form of hydrogen consists of a single proton and nothing else. A proton consists of component elementary particles: 2 up quarks and 1 down quark.
- Neutrons – The number of neutrons in an atom is commonly indicated using the letter N. A neutron is about the same size as a proton, but it is electrically neutral. Each neutron consists of 1 up quark and 2 down quarks.
- Electrons – Electrons are extremely tiny, compared with protons or neutrons. The mass of an electron is only 1/1836th that of a proton. Each electron carries a negative electrical charge. Each electron consists of a single elementary particle.
The atomic mass number of an atom is denoted by the symbol A and equals the sum of the number of protons and neutrons or Z + N.
Nucleus and Electron Shell
The parts of each atom are arranged to form a central core or atomic nucleus and an outer set of electron shells.
- Atomic Nucleus – Protons and neutrons collectively are termed nucleons because they bind together to form the nucleus of each atom.
- Electron Cloud – The electron shells describe regions in which an electron is most likely to be located. The innermost shell, the K shell, holds up to 2 electrons. The next shell, the L shell, holds up to 8 electrons. In reality, electrons swiftly spin around the atomic nucleus, but they do not have a well-defined orbit, like the Earth around the Sun. An electron could be just about anywhere (including, briefly, inside the nucleus). The high kinetic energy of the particles forms a sort of outer layer or cloud around an atom. Atoms appear solid, like little balls, because of the motion of electrons. It’s like how a fan blade looks like a solid disc when the fan is in motion.
Opposite electrical charges attract each other, so the protons and electrons are drawn toward each other. They don’t meet because the electrons are moving too quickly. It’s sort of like the Moon and the Earth. The Moon is drawn toward the Earth by gravity, but the two bodies don’t crash into each other because of their motion. The Moon is constantly falling around the Earth like electrons are falling around the atomic nucleus.
Ions and Isotopes
Ions and isotopes form when the number of different parts of the atom are changed.
Ions – An ion forms when the number of electrons is different from the number of protons. If there are more protons than electrons, a positively-charged ion called a cation forms. If there are more electrons than protons, the net charge is negative and the species is called an anion. Ions can be formed from single atoms or bound groups of atoms. An ion of a single atom is called an atomic ion.
Isotopes – Isotopes are atoms with the same number of protons, but different numbers of neutrons. There are stable isotopes, where the numbers of protons and neutrons remains the same over time, or radioisotopes. A radioisotope is an unstable or radioactive isotope, which will decay into a more stable isotope, releasing energy and sometimes particles.