In-Depth General Biology/1. The Inorganic Chemistry of Life
Everything in the universe consists of atoms, which are the fundamental components of matter, though not the smallest. Matter possesses mass, which is the amount of matter contained within, and volume, which is the space it occupies. Matter can be categorized into pure substances and mixtures. Pure substances are the foundational building blocks of matter, including elements and compounds, while mixtures are combinations of different types of compounds. Life is organized using these building blocks as a starting point.
ATOMS AND ELEMENTS
editUniverse is made of atoms. Atoms are the building blocks of matter and the universe. Atoms of the same kind conform elements, the smallest substances of all which cannot be separated in smaller components by any chemical or physical means. We currently know 118 chemical elements, but only around 90 are natural, and the rest are synthesized artifically. Living beings on Earth are made of six basic elements: carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Other elements like iron, calcium, potassium, molibdene, and magnese are called trace elements and are only present in small quantities in comparison with the most abundant elements (Table 1).
| Name | Chemical symbol | Percentage of Body Mass in Humans |
|---|---|---|
| Carbon | C | 18.5% |
| Hydrogen | H | 9.5% |
| Oxygen | O | 65.0% |
| Nitrogen | N | 3.3% |
| Phosphorus | P | 1.0% |
| Sulfur | S | 0.3% |
| Calcium | Ca | 1.5% |
| Potassium | K | 0.4% |
| Sodium | Na | 0.2% |
| Chlorine | Cl | 0.2% |
| Magnesium | Mg | 0.1% |
We order them in a grpahic representation called Periodic Table of Chemical Elements, organized in eighteen columns and seven rows which indicate some of the atom properties. Elements have trends we can follow and predict on the table. Some of these trends we'll study later.
Atomic structure
editAtom comes from greek, meaning "undivisable", coming from the original idea proposed by Democritus, who speculated in a sort of mental experiment that cutting in subsequent halves a grain of sand would require aroun 90 cuts to reach the atom level, a particle which cannot be torn apart. John Dalton took the idea in the 19th centruy and postulated his atomic theory. Atoms, basically are composed of three subatomic particles, particles smaller than an atom, called electron (with negative electric charge), proton (with positive electric charge) and neutron (no charge at all). Protons and neutrons stick together in the center of the atom, in a small region called atomic nucleus. Given protons have the same electric charge, they would repel each other, so they stick next to neutrons, who are uncharged, using strong nuclear force. Electrons circle the nucleus at high velocities forming some kind of electron cloud.
Electrons do not follow a predetermined orbit or trajectory, a phenomena called Heissenberg Uncertainty Principle: is not possible to predict fully the state in which a particle finds itself without altering, modifying or unknowing some results, like speed and position. We can only predict where they might be most of time. Atoms usually exist in three-dimensional spaces inside the electron cloud, called orbitals, each one, can be filled up with eight electrons. There are four kinds of orbital: s (like a sphere), p (like a dumbell), d and f (like flowers). Electrons have certain energy level, and can occupy orbitals with the same level of energy. Orbitals with the seme energy level make electronic shells, each with a limit in electron quantity, and represented by a letter ranging from K to Q (Table 2). Electrons in the most outermost shells are called valence electrons, and they're the most energetic of them all, something necessary as it allows to form chemical bonds and create molecules.