the electrons in the outermost energy level. The last shell.
Each period ends with a noble gas,
so all the noble gases have filled energy levels.
Russian Chemist DIM
taught chemistry in terms of properties, wrote down the elements in order of increasing mass, found some gaps, and predicted their properties before they were found.
are called periods.
are called groups.
Elements are placed in columns by
similar chemical properties.
are the elements in the A groups.
are the elements in the B groups.
are called Group 1A.
Alkaline earth metals
are called Group 2A.
are called Group 7A.
are called Group 8A.
Group 1 properties
metals, 1 valence electron, very reactive, soft, silver, shiny, low density (excluding hydrogen).
Group 2 properties
metals, 2 valence electrons, very reactive, less reactive than alkali metals, silver, more dense than alkali metals.
Group 3-12 properties
metals, 1 or 2 valence electrons, less reactive than alkaline-earth metals, shiny, good conductors of thermal energy and electric current, higher densities, melting points than elements in groups 1 and 2, and solid at room temperature except Mercury.
Group 17 properties
nonmetals, 7 valence electrons, very reactive, poor conductors of electric current, react violently with alkali metals to form salts, never found uncombined in nature.
Group 18 properties
nonmetals, 8 valence electrons, nonreactive, colorless, odorless gases at room temperature.
one-half the distance between the nuclei of identical atoms that are bonded together.
Ionization Energy (IE)
the energy required to remove one electron from a neutral atom of an element.