Core charge
Encyclopedia
Core charge is the effective nuclear charge
experienced by an outer shell electron
. In other words core charge is an expression of the attractive force experienced by the valence electron
s to the core of an atom
which takes into account the shielding effect
of core electron
s. Core charge can be calculated by taking the number of proton
s in the nucleus minus the number of core electrons, also called inner shell electrons, and is always a positive value.
Core charge is a convenient way of explaining trends in the periodic table. Since the core charge increases as you move across a row of the periodic table
, the outer-shell electrons are pulled more and more strongly towards the nucleus and the atomic radius
decreases. This can be used to explain a number of periodic trends such as atomic radius, first ionization energy (IE), electronegativity
, and oxidizing.
Core charge can also be calculated as 'atomic number' minus 'all electrons except those in the outer shell'. For example: Chlorine
(element 17), with electron configuration
1s2 2s2 2p6 3s2 3p5, has 17 protons and 10 inner shell electrons (2 in the first shell, and 8 in the second) so:
Effective nuclear charge
The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. The term "effective" is used because the shielding effect of negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge by the repelling effect...
experienced by an outer shell electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
. In other words core charge is an expression of the attractive force experienced by the valence electron
Valence electron
In chemistry, valence electrons are the electrons of an atom that can participate in the formation of chemical bonds with other atoms. Valence electrons are the "own" electrons, present in the free neutral atom, that combine with valence electrons of other atoms to form chemical bonds. In a single...
s to the core of an atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
which takes into account the shielding effect
Shielding effect
The shielding effect describes the decrease in attraction between an electron and the nucleus in any atom with more than one electron shell. It is also referred to as the screening effect or atomic shielding.-Cause:...
of core electron
Core electron
Core electrons are the electrons in an atom that are not valence electrons and therefore do not participate in bonding. An example: the carbon atom has a total of 6 electrons, 4 of them being valence electrons. So the remaining 2 electrons must be core electrons.They are so tightly bound to the...
s. Core charge can be calculated by taking the number of proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s in the nucleus minus the number of core electrons, also called inner shell electrons, and is always a positive value.
Core charge is a convenient way of explaining trends in the periodic table. Since the core charge increases as you move across a row of the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
, the outer-shell electrons are pulled more and more strongly towards the nucleus and the atomic radius
Atomic radius
The atomic radius of a chemical element is a measure of the size of its atoms, usually the mean or typical distance from the nucleus to the boundary of the surrounding cloud of electrons...
decreases. This can be used to explain a number of periodic trends such as atomic radius, first ionization energy (IE), electronegativity
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
, and oxidizing.
Core charge can also be calculated as 'atomic number' minus 'all electrons except those in the outer shell'. For example: Chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
(element 17), with electron configuration
Electron configuration
In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure...
1s2 2s2 2p6 3s2 3p5, has 17 protons and 10 inner shell electrons (2 in the first shell, and 8 in the second) so:
- Core charge = 17 − 10 = +7