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Valence electrons

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.

Horizontal rows

are called periods.

Vertical columns

are called groups.

Elements are placed in columns by

similar chemical properties.

Representative elements

are the elements in the A groups.

Transition elements

are the elements in the B groups.

Alkali metals

are called Group 1A.

Alkaline earth metals

are called Group 2A.

Halogens

are called Group 7A.

Noble gases

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.

Atomic radius

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.

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