THE PERIODIC TABLE and ELECTRON
ARRANGEMENTS WITHIN ATOMS
A periodic table is a tabular arrangement of the elements in
order of increasing atomic number such that elements having
similar chemical properties are positioned in vertical columns.
Elements within any given column of the periodic table exhibit
similar chemical behavior. Mendeleev (1834—1907) constructed
a periodic table. Element 101 carries his name.
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Groups and Periods of Elements
•
The location of an element within the periodic table is specified by
giving its period number, and group number.
• A period is a horizontal row of elements in the periodic table.
Elements in a period have the same number of energy shells or atomic
orbitals.
• A group is a vertical column of elements in the periodic table. The
chemical activity of metals within a given period increases with the
group number, while the chemical activity of non - metals within a
given period decreases with the group number.
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• The periodic table of the elements is a graphical way to show
relationships among the elements. Elements with similar chemical
properties fall in the same vertical column.
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METALS AND NONMETALS
• A metal is an element that has the characteristic properties of
luster, thermal conductivity, electrical conductivity, and
malleability. With the exception of mercury, all metals are
solids at room temperature (25 oC).
• A nonmetal is an element characterized by the absence of the
properties of luster, thermal conductivity, electrical
conductivity, and malleability. Many of the nonmetals, such as
hydrogen, oxygen, nitrogen, and the noble gases, are gases.
The only nonmetal found as a liquid at room temperature is
bromine. Solid nonmetals include carbon, iodine, sulfur, and
phosphorus. In general, the nonmetals have lower densities
and lower melting points than metals.
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Selected Physical Properties of Metals and Nonmetals
• *Except copper and gold.
• †Except mercury; cesium and gallium melt on a hot
summer day (85oF) or when held in a person’s hand.
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ELECTRON ARRANGEMENTS WITHIN ATOMS
• The space in which electrons move rapidly about a nucleus is
divided into subspaces called shells, subshells, and orbitals.
• Electron shell is a region of space about a nucleus that contains
electrons that have approximately the same energy. Electron shells
are numbered 1, 2, 3, and so on, outward from the nucleus.
Electron energy increases as the distance of the electron shell from
the nucleus increases. An electron in shell 1 has the minimum
amount of energy that an electron can have.
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The maximum number of electrons that an electron shell
can accommodate varies; the higher the shell number (n),
the more electrons that can be present. The lowest-energy
shell (n = 1) accommodates a maximum of 2 electrons. In
the second, third, and fourth shells, 8, 18, and 32 electrons,
respectively, are allowed.
The maximum number of electrons = 2n2
For example, when n = 4, the quantity 2n2 =2(4)2 = 32.
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• An electron subshell is a region of space within an electron shell
that contains electrons that have the same energy. The number
of subshells within a shell is the same as the shell number.
Subshells within a shell differ in size (that is, the maximum
number of electrons they can accommodate) and energy. The
higher the energy of the contained electrons, the larger the
subshell. Subshell size (type) is designated using the letters s, p, d,
and f. The lowest-energy subshell within a shell is always the s
subshell, the next highest is the p subshell, then the d subshell,
and finally the f subshell.
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• An s subshell can accommodate 2 electrons, a p subshell 6
electrons, a d subshell 10 electrons, and an f subshell 14 electrons.
Both a number and a letter are used in identifying subshells. The
number gives the shell within which the subshell is located, and
the letter gives the type of subshell. Shell 1 has only one subshell
— the 1s. Shell 2 has two subshells — the 2s and 2p. Shell 3 has
three subshells — the 3s, 3p, and 3d, and so on.
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An electron orbital is a region of space within an electron
subshell where an electron with a specific energy is most likely to
be found. An electron orbital, independent of all other
considerations, can accommodate a maximum of 2 electrons.
Thus an s subshell (2 electrons) contains one orbital, a p subshell
(6 electrons) contains three orbitals, a d subshell (10 electrons)
contains five orbitals, and an f subshell (14 electrons) contains
seven orbitals.
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ELECTRON CONFIGURATIONS AND ORBITAL DIAGRAMS
There are three rules, for assigning electrons to various shells,
subshells, and orbitals.
1. Electron subshells are filled in order of increasing energy.
2. Electrons occupy the orbitals of a subshell such that each
orbital acquires one electron before any orbital acquires a
second electron. All electrons in such singly occupied
orbitals must have the same spin.
3. No more than two electrons may exist in a given orbital —
and then only if they have opposite spins.
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The order of filling of various electron subshells is shown on
the right-hand side of this diagram. Above the 3p subshell,
subshells of different shells “overlap.”
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An electron configuration is a statement of how many
electrons an atom has in each of its electron subshells.
An orbital diagram is a notation that shows how many electrons
an atom has in each of its occupied electron orbitals. Note that
electron configurations deal with subshell occupancy and that
orbital diagrams deal with orbital occupancy. The orbital diagram
for the element nitrogen is
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The order for filling electron subshells with electrons follows the
order given by the arrows in this diagram.
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Order of filling of subshells in terms of increasing
energy
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Summary
Relationships involving electron shells, electron subshells, and
electron orbitals
Number of subshells in a shell = shell number
Maximum number of electrons in an s subshell = 2
Maximum number of electrons in a p subshell = 6
Maximum number of electrons in a d subshell = 10
Maximum number of electrons in an f subshell = 14
Maximum number of electrons in an orbital = 2
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