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Chemistry Terms and Their Meanings {A}

Here are some chemistry terms and their meanings. This will be useful to a lot of secondary school students.

α-carbon – An alpha carbon is the carbon in a molecule bonded to an atom or moiety of interest. α-carbon is the most common notation for the alpha carbon.

α-hydrogen – a hydrogen atom bonded to the α-carbon in a molecule. α-hydrogen is the most common notation for alpha hydrogen.

AbrasionRocks bang into each other and become smaller and more rounded.

Absolute zero – a theoretical condition concerning a system at zero Kelvin where a system does not emit or absorb energy (all atoms are at rest).

Absolute temperature – is temperature measured using the Kelvin scale where zero is absolute zero.

Acetal – an organic molecule where two separate oxygen atoms are single bonded to a central carbon atom. Acetals have the general structure of R2C(OR’)2.

An older definition of acetal had one at least one R group as a derivative of an aldehyde where R = H, but an acetal can contain derivatives of ketones where neither R group is a hydrogen. This type of acetal is called a ketal.

Acetals that contain different R’ groups are called mixed acetals. Acetal is also a common name for the compound 1,1-diethoxyethane. Dimethoxymethane is an example of an acetal compound.

Acetate – 1. acetate ion (CH3COO, C2H3O2) an ion formed by removing the acidic hydrogen from acetic acid.
2. a fiber made from cellulose acetate.
3. a compound resulting from replacing the acidic hydrogen in acetic acid.

Achiral – Achiral literally means “not chiral”. Achiral refers to an object which can be superimposed on its mirror image. Synonym: amphichiral

Methane is an example of an achiral molecule. The image shows methane’s structure and its mirrored reflection. The reflection can be rotated 180° to match up with the original structure.

Acid – a compound that, when dissolved in water, gives a pH of less than 7.0 or a compound that donates a hydrogen ion.

Acid catalysis – is a chemical reaction that requires the presence of an acid to act as a catalyst in order to proceed. The acid catalyst typically acts as a supply of protons to activate bonding sites in a molecule to induce a reaction.

Acid promoted – refers to a chemical reaction that needs an acid to proceed but does not act as a catalyst for the reaction. Reactions where the acid acts as a catalyst are acid catalysis reactions.

Acidulant – a food additive that lowers the pH to give a tart or bitter taste.

Acid rain –  All rainfall is slightly acidic because of the dissolved carbon dioxide. The term acid rain  refers to rain that is extra acidic because of large amounts of dissolved gases such as nitrogen oxides and sulfur oxides. These can make nitric acid and sulfuric acid as well as many others.

Active ingredient – a chemical or substance that has a biological effect. The term is applied to drugs, pesticides, herbicides, and herbal medicine. The other ingredients are termed excipients or inert ingredients. Excipients are either biologically nonreactive or else do not affect the biochemical process that is targeted by the product. A formulation may contain more than one active ingredient.

Also Known As: AI, Active Pharmaceutical Ingredient (API), bulk active, active substance, pharmacon, pharmakon

Acid anhydride – a compound with two acyl groups bound to a single oxygen atom. This is an oxide that forms an acid when it is reacted with water.
For example, when SO3 is added to water, it becomes sulfuric acid, H2SO4.

Acid dissociation constant – an equilibrium constant for the dissociation of a weak acid

Activated complex – a structure that forms because of a collision between molecules while new bonds are formed. The activated complex is the structure at the maximum energy point along the reaction path.

Activation energy – the minimum energy that must be input to a chemical system or minimum quantity of energy that the reacting species must possess in order to undergo a specified reaction. The least amount of energy needed for a chemical reaction to occur.

Activity SeriesThe activity series of metals is an list of metals ranked in order of decreasing reactivity to displace hydrogen gas from water and acid solutions. It can also be used to predict which metals will displace other metals in aqueous solutions. Also Known As: Reactivity Series of Metals. The activity series is a useful guide for predicting the products of metal displacement reactions. For example, placing a strip of zinc metal in a copper(II) sulfate solution will produce metallic copper and zinc sulfate, since zinc is above copper on the series.

Addition compound -a compound containing two or more simple compounds combined into an orderly defined crystal matrix. The two simple compounds are separated by a dot (·) in their formula.

Addition polymer – a polymer produced through the reaction of a monomer adding to itself. No further product is formed. The monomer is most commonly a derivative of ethylene.

Addition reactionA substance is reacted with an alkene to form a compound with a single bond between the two formerly double bonded carbon atoms. An example is the decolourisation of bromine.

Addition polymerisationOne long single molecule is made from many short chain monomers. All the starting material is incorporated in the final polymer. An addition reaction takes place each time the chain is extended.

Adenosine triphosphate – ATP is the acronym for the molecule adenosine triphosphate. The empirical formula of ATP is C10H16N5O13P3.

ATP is a nucleoside triphosphate made by bonding three phosphate groups to adenosine (adenine ring plus a ribose sugar). This organic compound often is termed the ‘energy currency’ of cellular metabolism because hydrolysis of the phosphate bonds releases considerable energy.

In addition to its function for intracellular energy transport, ATP serves as a substrate for enzymes that produce cyclic AMP (adenosine monophosphate) and phosphorylate lipids and proteins.

Adhesive – a material which bonds together the surfaces of two other materials. Examples: glues and cements

Aeration  – (also called aerification) is the process by which air is circulated through, mixed with or dissolved in a liquid or substance.

Air – The mixture of gases which we breathe! Most of the air (almost 4/5) is nitrogen with oxygen making up 1/5 and small amounts of argon (1%) and other gases in even smaller amounts. Carbon dioxide is only present in very small quantities. Water vapour is present in varying amounts depending on where you are in the world.

Air pollution – Substances that have been released into the air that are not natural. In the past, people have not been very concerned about waste being put into the atmosphere. Many thought that a tall chimney would remove the problem. Nowadays we are much more careful and take more care to dispose of problem gases, smoke and dusts in a more responsible way.

AllotropyThe existence of two or more crystalline or molecular structural forms of an element that have different chemical or physical attributes. Elements that can have different structures (and therefore different forms), such as Carbon (diamonds, graphite).

Aliphatic group – a functional group where the group is made up of carbon and hydrogen atoms and not aromatic. Example: The propyl functional group is an aliphatic group.

AlkaneA hydrocarbon that has only single bonds. It is a saturated hydrocarbon.

AlloyAn alloy is a mixture of metals or a mixture of a metal and another element. Alloys are defined by metallic bonding character. An alloy may be a solid solution of metal elements (a single phase) or a mixture of metallic phases (two or more solutions). A mixture of different metals. Bronze, brass, duralumin are some typical examples of alloys.

Allomer – A substance that has different composition than another, but has the same crystalline structure

Amorphous term used to describe a solid which does not exhibit crystalline structure. While there may be local ordering of the atoms or molecules in an amorphous solid, no long-term ordering is present.

Anion – Negatively charge ions. An ion with net negative charge, having more electrons than protons. In electrolysis, anions migrate to a positively charged anode.

Anode – The positive side of a dry cell battery or a cell by which electrons leave the cell. The anode has a positive charge because it is connected to the positively charged end of an external power supply. The positively charged element of an electrical device, such as a vacuum tube or a diode, to which electrons are attracted. The negative electrode of a voltaic cell, such as a battery.

Antioxidant – An antioxidant is defined as an enzyme or other organic molecule that can counteract the damaging effects of oxygen in tissues. Although the term technically applies to molecules reacting with oxygen, it is often applied to molecules that protect from any free radical (molecules with unpaired electron).
Examples: beta-carotene, lycopene, vitamin E.

Aqueous Solution – An aqueous solution is any solution in which water (H2O) is the solvent.
Examples: cola, saltwater, rain

Aromaticity – Chemical property of conjugated rings that results in unusual stability. See also benzene. In organic chemistry, the term aromaticity is used to describe a cyclic (ring-shaped), planar (flat) molecule with a ring of resonance bonds that exhibits more stability than other geometric or connective arrangements with the same set of atoms.

Arrhenius Acid and Base Definition: An Arrhenius acid is a substance that when added to water increases the number of H+ions in the water.
The H+ ion is also associated with the water molecule in the form of a hydronium ion, H3O+ and follows the reaction:
Acid + H2O → H3O+ + conjugate base.

An Arrhenius base is a substance that when added to water increases the number of OHions in the water.
Arrhenius bases follow the reaction:
Base + H2O → conjugate acid + OH

Astrochemistry – Astrochemistry is the chemistry of outer space. It is usually applied to regions beyond the solar system (which is sometimes termed cosmochemistry). Astrochemistry is an integration of astronomy and chemistry

Atom – A chemical element in its smallest form, and is made up of neutrons and protons within the nucleus and electrons circling the nucleus. An atom is a particle of matter that uniquely defines a chemical element. An atom consists of a central nucleus that is usually surrounded by one or more electrons. Each electron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons. The smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element.

Atomic ion – An atomic ion is an atom which has gained or lost at least one electron resulting in a net positive or negative charge on the atom.
Example: The hydride ion, H is an atomic ion

Atomic mass unitA unit of mass used to express atomic and molecular weights, equal to one-twelfth of the mass of an atom of carbon-12. It is equal to approximately 1.66 x 10-27 kg.

Atomic number – The number representing an element which corresponds with the number of protons within the nucleus. The number of protons or electrons normally found in an atom of a given chemical element. The higher the atomic number, the heavier the atom is. In a neutral atom, the number of protons and electrons is the same.

Atomic orbital – The region where the electron of the atom may be found. Atomic orbitals are regions of space around the nucleus of an atom where an electron is likely to be found. Atomic orbitals allow atoms to make covalent bonds. The most commonly filled orbitals are s, p, d, and f. S orbitals have no angular nodes and are spherical.

Atomic radiusThe atomic radius of a chemical element is a measure of the size of its atoms, usually the mean or typical distance from the center of the nucleus to the boundary of the surrounding cloud of electrons. the radius of an atom; the distance from the atomic nucleus to the outermost stable electron orbital in a atom at equilibrium; also, one-half the distance between nuclei of atoms of the same element, when the atoms are bound by a single covalent bond or are in a metallic crystal.

Average atomic mass The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance (the decimal associated with percent of atoms of that element that are of a given isotope). The natural abundance indicates the percentage of the isotope that is naturally found on the planet. The average atomic mass of an element refers to the atomic masses of the isotopes of the element, taking into account the different abundances of the element’s isotopes.

Avogadro’s lawAvogadro’s law states that, “equal volumes of all gases, at the same temperature and pressure, have the same number of molecules”. For a given mass of an ideal gas, the volume and amount (moles) of the gas are directly proportional if the temperature and pressure are constant.

Avogadro’s numberAvogadro’s number is defined as the number of elementary particles (molecules, atoms, compounds, etc.) per mole of a substance. It is equal to 6.022×10 23 mol 1 and is expressed as the symbol N A. Avogadro’s number is a similar concept to that of a dozen or a gross. A dozen molecules is 12 molecules.

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