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Valence Electrons Periodic Table


Electrons in an atom are distributed in various sub shells according to Pauli's principle and Hund's rule. Every electron has orbital angular momentum and spin angular momentum. Electrons exist in a part of the atom called the electron cloud. The valence shell is the outermost part of this cloud. In every atom, there are electrons in the electron cloud and in the valence shell. These valence electrons determine whether something is a conductor, a semiconductor or an insulator.

The number of of valence electrons those in the outer shell is the same for all the atoms in the group and is equal to the group number. The outer shell of an atom is known as the valence shell and the electrons in it are called the valence electrons. The valence electrons are extremely important because they are the ones involved in forming chemical bonds. Elements in a given group have the same number of valence electrons and therefore have similar chemical properties.

Determining Valence Electrons from Periodic Table

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In general the number of valence electrons of an atom equals its group number. In the new IUPAC system for numbering groups, this holds except in the p block. In older periodic tables the number of valence electrons equals the group number as long as the groups in a given part of the periodic table are consecutively numbered. Toward the end of the transition metals the numbering is not consecutive so that we must continue numbering upward.

The groups of f-block elements are not numbered at all in a conventional periodic table, so that we must count over from La and Ac as "3" or Ce and Th as "4". Then Lu ans Lr should be numbered as having three valence electrons.

Periodic Table with Valence Electrons

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Knowing the number of valence electrons of an atom is important in deriving some of fundamental periodic variables we will use in organizing the chemistry of the elements. One of the justifications for grouping elements as we do in the periodic table is that elements in a group of the periodic table have the same number of valence electrons in the same shapes of orbitals.

The ns ans np electrons are the valence electrons for main group elements. The chemical behavior of an element is determined by valence electrons. Valence electrons for transition elements include the electrons in the ns and (n-1)d orbitals. Arranging the valence electrons of a main group element around an atom in four groups suggests that the valence shell can accommodate four pairs of electrons.

The visual layout of the periodic table is convenient for determining the electron configuration of an atom. The valence electrons on periodic table is shown below.

Periodic Table with Valence Electrons

Valence Electron Configuration Periodic Table

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The periodic table was an empirical construction. However it is fundamentally understandable in terms of the electron configurations. The chemical and many physical properties of the elements are simply controlled by the valence electrons. The valence electron configuration varies in a systematic and repetitive way as the various shells are filled. This leads naturally to both the periodicity and the repetitive features displayed in the periodic table.

Valence Electron Configuration Periodic Table

The above diagram shows the relationship between the outer orbitals that are partly filled and the position of the element in the periodic table. The filled shells are very stable configurations and take part in chemical reactions only under extreme conditions. The atoms with this configuration, the noble gases are placed in Group 18 of the periodic table.

The alkaline metals are in Group 1 of the periodic table all have two valence electrons both in the outermost s orbital. Thus the periodic table simply expresses the Aufbau principle

Facts About the Periodic Table

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Rows and columns

The periodic table of elements is laid out in rows called periods and columns called groups.

Electron shells

Electrons spin round atoms in up to 7 layers or "shells". There is a limit to how many electrons that can fit in each shell. Only 2 fit in the first shell in the first shell, closest to the nucleus 8 in the second and 8 in the third. After that it gets complicated  but the outer shell never holds more than 8.

Shells and Periods

The number of electron shells an atom has increases down each group. So enery atom in each period has the same number of electron shells.

Electrons and Groups

Each group is for elements with a certain number of electrons in their outer shells and this is what determines an elements chemical properties. Every element in the same Group has similar properties.

Reactive to stable

Each period starts on the left with a highly reactive "alkali metal" which has one electron in its outer shell. It ends on the right with a stable "noble gas" such as argon, which has eight electrons in its outer shell.