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Electron Configuration and the Periodic Table
Periods and Blocks of the Periodic Table
While the elements are arranged vertically in the periodic table in groups that share similar chemical properties, they are
also organized horizontally in rows, or periods
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Also, the period of an element can be determined from the element’s
electron configuration
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The s-Block Elements: Groups 1 and 2
The elements of the s block are chemically reactive metals
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The outermost energy level in an atom of each Group 1 element contains a single s electron
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In their
pure state, all of the alkali metals have a silvery appearance and are soft enough to cut with a knife, however, because they
are so reactive, alkali metals are not found in nature as free elements
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They react strongly to water to produce hydrogen gas and aqueous solutions of substances known as alkalis
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The elements of Group 2 of the periodic table (beryllium, magnesium, calcium, strontium, barium, and radium) are called
the alkaline-earth metals
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Consequently, the group configuration for Group 2 is ns
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They also have higher melting points
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Hydrogen and Helium
Hydrogen has an electron configuration of 1s , but despite the ns configuration, it does not share the same properties as
the elements of Group1
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Like the Group 2 elements, helium has an ns group configuration
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Because its highest
occupied energy level is filled by two electrons, helium possesses special chemical stability, exhibiting the unreactive
nature of a Group 18 element
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The d-Block Elements: Groups 3-12
For energy level n, there are n possible sublevels, so the d sublevel first appears when n = 3
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This order of filling is also seen for higher
values of n
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Group 3 elements each have one electron in the d sublevel of the (n-1) energy level
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Atoms of the Group 12 elements have 10 electrons in the d sublevel
plus two electrons in this sublevel
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Notice, however, that in each case the sum of the outer s and d electrons is equal to the group number
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They
are good conductors of electricity and have a high luster, and typically less reactive than the alkali metals and the alkalineearth metals
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The p-block elements together with the
s-block elements are called the main-group elements
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At its
right-hand end, the p block includes all of the nonmetals except hydrogen and helium
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At the left-hand side and bottom of the
block, there are eight p-block metals
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The halogens
are the most reactive nonmetals
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The metalloids, or semiconducting elements, are located between nonmetals and metals in the p block
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The metalloid elements have
electrical conductivity intermediate between that of metals, which are good conductors, and nonmetals, which are
nonconductors
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With the exception of bismuth, these metals are sufficiently reactive to be found in nature only in
the form of compounds
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The f-Block Elements: Lanthanides and Actinides
In the periodic table, the f-block elements are wedged between Groups 3 and 4 in the sixth and seventh periods
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With seven 4f orbitals to be filled with two
electrons each, there are a total of 14 f-block elements between lanthanum, La, and hafnium, Hf, in the sixth period
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There are also 14-blcok elements,
the actinides, between actinium, Ac, and element 104, Rf, in the seventh period
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The actinides are all radioactive
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The remaining actinides are known only as laboratory-made elements

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