Download In the periodic table, the elements are placed from left to right in

In the periodic table, the elements are placed from left to right in each
period in the sequence of their atomic numbers.
LEARNING OBJECTIVE [ edit ]
Identify the general trends in chemical properties of elements based on their position in the
periodic table.
KEY POINTS [ edit ]
Elements tend to adopt the stable electron configurations of the noble gases.
The s block includes the first two groups (alkali metals andalkaline earth metals) as well as
hydrogen and helium.
The p block includes the last six groups, Groups 13 to 18, and contains, among others, all of
the metalloids and nonmetals.
The d block includes Groups 3 to 12 and contains all of the transition metals.
The f block, usually offset below the rest of the periodic table, includes
the lanthanides and actinides.
TERMS [ edit ]
valence
The combining capacity of an atom, radical or functional group determined by the number of
electrons that it will lose, gain, or share when it combines with other atoms, etc.
electronegativity
The tendency of an atom or molecule to attract electrons and thus form bonds.
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Structure of the Periodic Table
The periodic table displays all the chemical elements organized by atomic
number and electron configuration. Specifically, elements are presented by increasing
atomic number. The main body of the table is an 18 by 7 grid, and elements with the same
number of valence electrons are kept together in groups (columns), such as the halogens and
the noble gases. The table has four distinct rectangular areas, or blocks. The f block is usually
included below the main table rather than within it to minimize the table's width. The trends
in the periodic table can help predict the properties of various elements and the relations
between properties. As a result, the periodic table is a useful framework for analyzing
chemical behavior and as such is widely used in chemistryand other sciences.
Groups
A group, or family, is a vertical column in the periodic table. Elements in the same group
show patterns in atomic radius,ionization energy, and electronegativity. From top to bottom
in a group, the atomic radii of the elements increase: since there are more filled energy
levels, valence electrons are found farther from the nucleus. From top to bottom, each
successive element has a lower ionization energy because it is easier to remove an electron
since the atoms are less tightly bound. Similarly, from top to bottom, elements decrease in
electronegativity due to an increasing distance betweenvalence electrons and the nucleus.
There are exceptions to these trends however – in Group 11, for example, the
electronegativity increases down the group.
Periods
Elements in the same period show trends in atomic radius, ionization energy, electron
affinity, and electronegativity. Moving left to right across a period, from the alkali metals to
the noble gases, atomic radius usually decreases. This is because each successive element has
an additional protonand electron, which causes the electrons to be drawn closer to the
nucleus. The additional proton increases the effective nuclear charge to a greater extent than
the addition of an extra electron to an already partially­filled shell. The decrease in atomic
radius also causes ionization energy to increase from left to right across a period: the more
tightly bound an element is, the more energy is required to remove an electron.
Electronegativity increases in the same manner as ionization energy because of the pull
exerted on the electrons by the nucleus. Electron affinity also shows a slight trend across a
period: metals (the left side of a period) generally have a lower electron affinity than
nonmetals (the right side of a period), with the exception of the noble gases which have an
electron affinity of zero.
Blocks
Because of the importance of the outermost electron shell, the different regions of the
periodic table are sometimes referred to as blocks, named according to the subshell in which
the "last" electron resides. The s block includes the first two groups (alkali metals and
alkaline earth metals) as well as hydrogen and helium. The p block includes the last six
groups, which are Groups 13 to 18 in IUPAC (3A to 8A in American), and contains, among
others, all of the metalloids. The d block includes Groups 3 to 12 in IUPAC (or 3B to 2B in
American group numbering) and contains all of the transition metals. The f block, usually
offset below the rest of the periodic table, includes the lanthanides and actinides.
Blocking in the periodic table
The periodic table can be broken into blocks, corresponding to the highest energy electrons.
Periodicity
The primary determinant of an element's chemical propertiesis its electron configuration,
particularly that of the valence shell electrons. For instance, all atoms with four valence
electrons occupying p orbitals will share some similar characteristics. The type of orbital in
which the atom's outermost electrons reside determines the "block" to which that element
belongs. The number of valence shell electrons determines the family, or group, to which the
element belongs. The total number of electron shells an atom has determines the period to
which it belongs. Each shell is divided into different subshells. Since the outermost electrons
determine chemical properties, those with the same number of valence electrons are
generally grouped together.