Chemical Bonds

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Slide 9

The periodic table

By the late 1800’s it was realized that elements could be grouped by similar chemical properties and that the chemical and physical properties of elements are periodic functions of their atomic numbers – PERIODIC LAW.

The arrangements of the elements in order of increasing atomic number, with elements having similar properties placed in a vertical column, is called the PERIODIC TABLE.

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Columns are called GROUPS (FAMILIES) and rows are called PERIODS.

Elements in a group have similar chemical and physical properties.

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The total number of electrons within a group is different, increasing in number down a group

However, the number of electrons furthest away from the nucleus, called the OUTER or VALENCE electrons is the same for all elements in a group.

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Groups are referred to by names, which often derive from their properties

I – Alkali metals; II – Alkaline Earth metals

VII – Halogens; VIII – Noble gases

The elements in the middle block are called TRANSITION ELEMENTS

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Elements in the A group are diverse; metals and non-metals, solids and gases at room temperature.

The transition elements are all metals, and are solids at room temp, except for Hg.

Among the transition elements are two sets of 14 elements - the LANTHANIDES and the ACTINIDES

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Physical and Chemical properties such as melting points, thermal and electrical conductivity, atomic size, vary systematically across the periodic table.

Elements within a column have similar properties

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Atomic radius (Å)

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A “zig-zag” division of the table divides metals from non-metals.

Elements to the left of the zig-zag line are metals (except for hydrogen, which is unique) and to the right are non-metals.

Elements along the border have intermediate properties and are called metalloids.

TABLE

Slide 20

Electronegativity