This chemistry dictionary offers the chemistry definitions starting with the letter E. These glossary terms are commonly used in chemistry and chemical engineering. Click the letter below to find the terms and definitions beginning with that letter.
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
earths – Earths is an alchemical and old chemical term for compounds were thought to be elements but were later discovered to be metal oxides.
ebullition – a phase transition from the liquid state to the gas state, usually occurring when a liquid is heated to its boiling point.Also known as: boilingExample: Boiling is seen when water is heated until it forms steam
EC – EC stands for Electron Capture. See the electron capture definition below.
eclipsed conformation – Eclipsed conformation is the conformation that occurs when the dihedral angle between two atoms or groups of atoms is 0°. The atoms or groups of atoms around the single bond align with each other where they would overlap or eclipse each other if viewed along the axis of rotation.
effective nuclear charge – The effective nuclear charge is the net charge an electron experiences in an atom with multiple electrons. Higher energy electrons can have other lower energy electrons between the electron and the nucleus, effectively lowering the positive charge experienced by the high energy electron.Example: A 2s lithium electron can have 2 1s electrons between itself and the lithium nucleus. Measurements indicate the effective nuclear charge experienced by a 2s lithium electron is 0.43 times the charge of the lithium nucleus.
effervescence – Effervescence is the foaming formed as a result of a gas being evolved from a solid or liquid.
efflorescence – Efflorescence is the process of losing the water of hydration from a hydrate compound.
effusion – Effusion is the movement of a gas through a pore or capillary into another gaseous region or into a vacuum.
Einstein’s equation – the relation ΔE = Δmc2, relating energy and mass changes, where E is energy, m is mass, and c is the speed of light.
einsteinium – Einsteinium is the name for the actinide element with atomic number 99 and is represented by the symbol Es.
elastic – A substance is elastic if substance returns to its original shape after being deformed.
elasticity – Elasticity is a physical property of a material where the material returns to its original shape after being deformed.
elastic limit – Elastic limit is the maximum amount of force that can be applied to a substance before it is no longer elastic.
elastomer – An elastomer is a polymer that can be stretched and returns to its original shape without permanent deformation.Example: Natural rubber is an elastomer.
electric circuit – A circuit is a closed path through which electric current can flow. The current can flow in the form of free electrons or as ions.
electrical conductivity – Electrical conductivity is the measure of the amount of electrical current a material can carry. Electrical conductivity is denoted by the symbol σ and has SI units of siemens per meter (S/m).
electrical resistivity – Electrical resistivity is the measure of how much a material resists carrying an electrical current. Electrical resistivity is denoted by the symbol ρ and has SI units of ohm meter (Ωm).
electric dipole – An electric dipole is formed when the centers of positive charges and negative charges do not coincide.Example: Polar molecules are electric dipoles.
electric field – An electric field is a field around charged particles and changing magnetic fields which exert a force on charges within the field. Electric field is defined as the electrical force expressed on a stationary positive charge.
electrochemical cell – An electrochemical cell is a device that generates a potential difference between electrodes using chemical reactions.Examples: Galvanic cells and electrolytic cells are examples of electrochemical cells.
electrochemistry – Electrochemistry is the scientific study of the chemical species and reactions that take place at the interface between an electron conductor and an ion conductor (electrolyte) in which an electron transfer occurs between the electrode and the electrolyte in solution.
electromotive force – emf – Electromotive force is the electric potential generated by either an electrochemical cell or a changing magnetic field. Electromotive force is commonly denoted by the acronym emf, EMF or a cursive letter E ( ℰ ). The SI unit for electromotive force is the volt.Also known as: voltage, emf
electrode – An electrode is a general term applied to the either the anode or cathode of an electrochemical cell.
electrode potential – Electrode potential is the potential difference between the electrode and its solution.
electrokinetic potential – The electrokinetic potential is defined as the potential difference across phase boundaries between solids and liquids. In colloids, the electrokinetic potential is the electric potential difference across the ionic layer around a charged colloid ion. Typically, the higher the electrokinetic potential, the more stable the colloid. When the zeta-potential equals zero, the colloid will precipitate into a solid.Also known as: zeta potential
electrolysis – Electrolysis is the passage of a direct electric current through an ion-containing solution. Electrolysis produces chemical changes at the electrodes.
electrolyte – A substance which forms ions in an aqueous solution.Examples: NaCl forms Na+ and Cl– in water.
electrolytic cell – Electrolytic cell is a type of chemical cell in which the flow of electric energy from an external source causes a redox reaction to occur.
electromagnetic radiation – Electromagnetic radiation is self-sustaining energy with electric and magnetic field components. Electromagnetic radiation is commonly referred to as ‘light’.Also known as: light, EMR, EM radiation, electromagnetic waves
electron – An electron is a negatively charged component of an atom. Electrons exist outside of and surrounding the atom nucleus. Each electron carries one unit of negative charge and has a very small mass as compared with that of a neutron or proton.
electron affinity – Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have greater electron affinity.Example: The electron affinity of hydrogen is ΔH in the reactionH(g) + e– → H–(g); ΔH = -73 kJ/mol.
electron capture – Electron capture is a type of radioactive decay where the nucleus of an atom absorbs a K or L shell electron and converts a proton into a neutron. This process reduces the atomic number by 1 and emits gamma radiation and a neutrino. The decay scheme for electron capture is:ZXA + e– → ZYA-1 + ν + γwhereZ is the atomic massA is atomic numberX is the parent elementY is daughter elemente– is an electronν is a neutrinoγ is a gamma photonAlso known as: EC, K-capture (if K shell electron is captured), L-capture (if L shell electron is captured)Example: Nitrogen-13 decays to Carbon-13 by electron capture.13N7 + e– → 13C6 + ν + γ
electron cloud – The electron cloud is the region of negative charge surrounding an atomic nucleus that is associated with an atomic orbital.
electron configuration – Electron configuration is a statement describing the populations of electronic energy sublevels of an atom. See the chart of electronic configurations to get the notation for all of the elements.Example: The electronic configuration of the lithium atom is 1s22s, which indicates there are two electrons in the 1s sublevel and one electron in the 2s energy sublevel.
electron density – Electron density is a representation of the probability of finding an electron in a specific location around an atom or molecule. In general, the electron is more likely to be found in regions with high electron density.
electron domain – Electron domain refers to the number of lone pairs or bond locations around a particular atom in a molecule. Bond location is independent of whether the bond is a single, double or triple bond. Electron domain is used in VSEPR theory to determine the molecular geometry of a molecule.
electronegativity – Electronegativity is a property of an atom which increases with its tendency to attract the electrons of a bond.Example: The chlorine atom has a higher electronegativity than the hydrogen atom, so the bonding electrons will be closer to the Cl than to the H in the HCl molecule.
electron pair – An electron pair is a pair of electrons in one orbital which have opposite spins or a pair of electrons in a covalent or coordinate bond.
electron pair repulsion – Electron pair repulsion is the principle that electron pairs around a central atom tend to orient themselves as far apart as possible. Electron pair repulsion is used to predict the geometry of a molecule or a polyatomic ion.
electron-sea model – The electron sea model is a model of metallic bonding in which cations are considered to be fixed points within a mobile ‘sea’ of electrons.
electron shell – An electron shell is a set of atomic electrons grouped together by their quantum energy levels.
electron spin – Electron spin is a property of an electron that is loosely related to its spin about an axis. Two electron spin states are allowed, which are described by the quantum number ms, with values of +½ or -½.
electron volt – The electron volt is a unit of energy. One electron volt (eV) is equal to the change in energy as an unbound electron passes through a potential difference of one volt. 1 eV = 1.602176487(40)x10−19 J
electrophile – An electrophile is an atom or molecule that accepts an electron pair to make a covalent bond.Also known as: Lewis acidExamples: H+ is an electrophile. It can accept a pair of electrons from the Lewis base OH– to form H2O.
electroplating – Electroplating is a process where a coating of metal is added to a conductor using electricity via a reduction reaction. When a current is applied to the conductor to be coated, metal ions in solution are reduced onto the electrode to form a thin layer.
electrostatic forces – Electrostatic forces are the forces between particles that are caused by their individual electric charges.
electrum – Electrum is a naturally-occurring alloy of gold and silver with a few other metals. The man-made alloy of gold and silver is chemically similar to electrum, but usually, is called green gold.
element – A chemical element is a substance that cannot be broken down by chemical means. Elements are defined by the number of protons they possess.
elementary reaction – An elementary reaction is a chemical reaction where reactants form products in a single step.
element symbol – Element symbol refers to the one- or two-letter abbreviation for a chemical element, though the term can be applied to the alchemical symbols as well.Examples: H for hydrogen, He for helium, Ca for calcium
ELF – ELF is an acronym for Extremely Low Frequency. In general, ELF refers to the part of the electromagnetic spectrum with frequencies from 1 to 300 Hz. In radio and atmospheric studies, ELF refers to radio waves with frequencies between 30 and 3000 Hz.Also known as: extremely low frequency