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The elements in a horizontal row of the periodic table.

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Sigma Orbital

Molecular orbital resulting from head-on overlap of two atomic orbitals.

Primary Standard

A substance of a known high degree of purity that undergoes one invariable reaction with the other reactant of interest.

Bond Energy

The amount of energy necessary to break one mole of bonds of a given kind (in gas phase).The amount of energy necessary to break one mole of bonds in a substance, dissociating the sustance in the gaseous state into atoms of its elements in the gaseous state.

Solution

Homogeneous mixture of two or more substances.

Atomic Number


Integral number of protons in the nucleus, defines the identity of element.
 

London Forces

Very weak and very short-range attractive forces between short-lived temporary (induced) dipoles, also called dispersion Forces.

Matter

Anything that has mass and occupies space.

Fossil Fuels

Substances consisting largely of hydrocarbons, derived from decay of organic materials under geological conditions of high pressure and temperature (metamorphism) include coal, petroleum, natural gas, peat and oil shale.  For further information see Fuel Chemistry

Absolute Entropy (of a substance)

The increase in the entropy of a substance as it goes from a perfectly ordered crystalline form at 0 °K (where its entropy is zero) to the temperature in question.

Entropy is a measure of the “dilution” of thermal energy.

Stoichiometry

Description of the quantitative relationships among elements and compounds as they undergo chemical changes.