Atoms

Atoms are the smallest divisible components of matter that have the same properties (e.g. size, shape, mass) which differ from the properties of other elements. They are the fundamental units of each mineral’s crystal structure. Each atom consists of a tiny nucleus that contains equal numbers of positively-charged protons and electrically neutral neutrons. This nucleus is surrounded by one or more shells of negatively-charged electrons.

  • Ion: an atom (or a molecule) in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge.
  • Anion: an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged).
  • Cation: an ion with fewer electrons than protons, giving it a positive charge.
  • Atomic number: the number of protons present in an atom’s nucleus.
  • Atomic mass: the mass of an atom of an element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number).
  • Valence: the number of lost or gained electrons; this quantity dictates how much “combining” power an atom has to form molecules.

Element

An element is the simplest form of matter that can exist under conditions that we find in a laboratory. There are 118 elements that have been identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements.

In geological terms, we can subdivide the elements into four main groups according to their reactivity (i.e. what elements they commonly combine with) and where they occur in the Earth:

  • Lithophile: elements that commonly occur with oxygen within Earth’s crust.
  • Chalcophile: elements that commonly occur with sulfur in Earth’s crust and mantle.
  • Siderophile: elements that commonly occur with iron in Earth’s mantle and core.
  • Atmophile: elements that commonly occur in Earth’s atmosphere.

Periodic Table

Periodic-Table-Color
Periodic Table courtesy of sciencenotes.org

The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configurations and recurring chemical properties. This ordering shows periodic trends, such as elements with similar behavior in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the left, and non-metals on the right.

The rows of the table are called periods; the columns are called groups. Six groups (columns) have names as well as numbers: for example, group 17 elements are the halogens; and group 18, the noble gases. The periodic table can be used to derive relationships between the properties of the elements, and predict the properties of new elements yet to be discovered or synthesized. The periodic table provides a useful framework for analyzing chemical behavior, and is widely used in chemistry and other sciences.

Elements in minerals

The most common elements that we encounter within minerals are: aluminum, barium, carbon, calcium, chlorine, copper, fluorine, iron, hydrogen, potassium, magnesium, manganese, sodium, oxygen, phosphorous, lead, sulfur, silicon, titanium and zinc.

Compounds

A compound is a group of atoms of a fixed ratio bound so tightly together that they behave as a single particle. A stoichiometric compound is one in which all the charges are balanced.

Terms

Empirical or simplest formula: simply gives the relative number of atoms of each element present (e.g. ethylene: CH2)

Molecular formula: gives the actual number of each atom found in a molecule (e.g. ethylene: C2H4)

Isotopes: can be formed by either the radioactive decay of unstable nuclides ( radiogenic isotopes – e.g. U, Pb, Sr, Ar, Nd) or by exchange or kinetic reactions in nonradiogenic elements (commonly referred to as stable isotopes – e.g. O, H, C, S). Isotopes of an element have the same atomic number but different atomic weights

Mixture: a combination of elements or compounds in no fixed ratios (can usually be broken-down into their constituent compounds and/or elements by physical processes)

Phase: any part of a system that has uniform composition and properties

Bonding

Bonds are forces that hold atoms in their places. Within minerals, there are four main types of bonds called metallic bonds, covalent bonds, ionic bonds and van der Waals bonds.

  • Metallic bonds: are the most common type within native metals. Metallic bonding occurs when electrons can move freely from one ion to another.
  • Covalent bonds: are rarely the predominant type in minerals. In the diamond structure, a central carbon atom is surrounded by four other carbon atoms each of which shares an electron with the central carbon atom.
  • Ionic bonds: are the most important in 90% of all minerals. Each ion is surrounded by ions of opposite charge, with the number of ions being dependent upon their ionic radii and charges.
  • Van der Waals bonds: are weak dipolar bonds between molecules, such as those that are responsible for the cohesion of water molecules.