Covalent radiusThe covalent radius, rcov, is a measure of the size of an atom that forms part of one covalent bond. It is usually measured either in picometres (pm) or angstroms (Å), with 1 Å = 100 pm. In principle, the sum of the two covalent radii should equal the covalent bond length between two atoms, R(AB) = r(A) + r(B). Moreover, different radii can be introduced for single, double and triple bonds (r1, r2 and r3 below), in a purely operational sense.
Charge radiusThe charge radius of an atomic nucleus tells its size. The nucleus (center) of an atom is incredibly tiny. A nucleus, as with an atom, is actually a hazy quantum-mechanical wave-cloud, because each of the particles inside it are also hazy wave-clouds. Not having a definite surface, the cutoff is usually statistical, and can be calculated in a variety of ways. The rms charge radius is a measure of the size of an atomic nucleus, particularly the proton distribution.
Van der Waals radiusThe van der Waals radius, rw, of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom. It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, as he was the first to recognise that atoms were not simply points and to demonstrate the physical consequences of their size through the van der Waals equation of state.Ionic radiusIonic radius, rion, is the radius of a monatomic ion in an ionic crystal structure. Although neither atoms nor ions have sharp boundaries, they are treated as if they were hard spheres with radii such that the sum of ionic radii of the cation and anion gives the distance between the ions in a crystal lattice. Ionic radii are typically given in units of either picometers (pm) or angstroms (Å), with 1 Å = 100 pm. Typical values range from 31 pm (0.3 Å) to over 200 pm (2 Å).
Covalent bondA covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding. For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full valence shell, corresponding to a stable electronic configuration.
Atomic nucleusThe atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford at the University of Manchester based on the 1909 Geiger–Marsden gold foil experiment. After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg.
Chemical elementChemical substance not composed of simpler onesThe chemical elements ordered in the periodic table, as shown in the 32-column formatA chemical element is a species of atom defined by its number of protons. The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8: each oxygen atom has 8 protons in its nucleus.
AtomSmallest unit of a chemical elementAtoms are the basic particles of the chemical elements and the fundamental building blocks of matter. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that contains 11 protons is sodium, and any atom that contains 29 protons is copper.
ElectronThe electron (e, or β in nuclear reactions) is a subatomic particle whose electric charge is negative one elementary charge. It is an elementary particle contained in the matter that makes up the universe. All atoms are composed of electrons, as well as varying numbers protons and neutrons, but the electrons have almost 2,000 times less mass than the other two constituents.
MoleculeA molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and molecule is often used when referring to polyatomic ions.
Metallic bondingMetallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. Metal atoms lose their valence electrons to a large, delocalized orbital, which leaves the nucleus, and other electrons that are closer to the nucleus, as positively charged cations.
Condensed matter physicsCondensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquidphases, that arise from electromagnetic forces between atoms and electrons. More generally, the subject deals with condensed phases of matter: systems of many constituents with strong interactions among them.*As an Amazon Associate I earn from qualifying purchases.