Molecules - Key terms
AVOGADRO'S NUMBER:
A figure, named after Italian physicist Amedeo Avogadro (1776-1856), equal to 6.022137 × 10 23 . Avogadro's number indicates the number of molecules in a mole.
BOND ENERGY:
The energy required to pull apart the atoms in a chemical bond.
CHEMICAL BONDING:
The joining, through electromagnetic force, of atoms representing different elements.
COMPOUND:
A substance made up of atoms of more than one element. These atoms are usually joined in molecules.
COVALENT BONDING:
A type of chemical bonding in which two atoms share valence electrons.
DIATOMIC:
A term describing an element that exists as molecules composed of two atoms.
DIPOLE-DIPOLE ATTRACTION:
A form of intermolecular bonding between molecules formed by a polar covalentbond.
ELECTRON:
A negatively charged particle in an atom.
ELECTRONEGATIVITY:
The relative ability of an atom to attract valence electrons.
EMPIRICAL FORMULA:
A chemical formula that shows the smallest possible whole-number ratio of the atoms involved. Compare with molecular formula and structural formula.
HYDROGEN BONDING:
A kind of dipole-dipole attraction between molecules formed of hydrogen along with an element having a high electronegativity.
INTERMOLECULAR BONDING:
The bonding that exists between molecules. This is not to be confused with chemical bonding, the bonding of atoms within a molecule.
ION:
An atom or group of atoms that has lost or gained one or more electrons, and thus has a net electric charge.
IONIC BONDING:
A form of chemical bonding resulting from attractions between ions with opposite electric charges.
ISOMERS:
Substances having the same chemical formula, but which are chemically dissimilar due to differences in the arrangement of atoms.
LONDON DISPERSION FORCES:
A term describing the weak intermolecular bond between molecules that are not formed by a polar covalent bond.
MOLE:
The SI fundamental unit for "amount of substance." A mole is, generally speaking, Avogadro's number of molecules; however, in the more precise SI definition, a mole is equal to the number of carbon atoms in 12.01 g of carbon.
MOLECULAR FORMULA:
A chemical formula that indicates the types and numbers of atoms involved, showing the actual proportions of atoms in a molecule. Compare with empirical formula and structural formula.
MOLECULAR SOLID:
A form of crystalline solid—a solid in which the constituent parts have a simple and definite geometric arrangement repeated in all directions—in which the molecules have a neutral electric charge. Table sugar (sucrose) is an example.
MOLECULE:
A group of atoms, usually but not always representing more than one element, joined in a structure. Compounds are typically made up of molecules.
OCTET RULE:
A term describing the distribution of valence electrons that takes place in chemical bonding for most elements, which end up with eight valence electrons.
POLAR COVALENT BONDING:
The type of chemical bonding between atoms that have differing values of electronegativity. Water molecules are an example of a polar covalent bond.
SHELL:
The orbital pattern of the valence electrons at the outside of an atom.
STEREOCHEMISTRY:
The area of chemistry devoted to the three-dimensional arrangement of atoms in a molecule.
STRUCTURAL FORMULA:
A diagram that shows how the atoms are bondedtogether, complete with lines representing covalent bonds. Compare with empirical formula and molecular formula.
VALENCE ELECTRONS:
Electrons that occupy the highest energy levels in anatom. These are the only electrons involved in chemical bonding.
VALENCY:
The property of the atom of one element that determines its ability to bond with atoms of other elements.
VSEPR (VALENCE SHELL ELECTRON PAIR REPULSION) MODEL:
A means of representing the three-dimensional structure of atoms in a molecule.