Definition of electronegativity
Electronegativity comprehensively considers ionization energy and electron affinity energy, which was first proposed by linus pauling in 1932. The relative size of a set of values is used to express the attraction of element atoms to bonding electrons in molecules, which is called relative electronegativity. The greater the electronegativity of elements, the stronger the attraction of atoms to bonding electrons when forming chemical bonds.
Calculation method of electronegativity
There are many methods to calculate electronegativity, and the electronegativity value of each method is different. There are three representative methods:
(1) the scale proposed by Pauling. According to the thermochemical data and the bond energy of molecules, the electronegativity of fluorine is designated as 3.98, and the relative electronegativity of other elements is calculated.
② Absolute electronegativity is calculated by ② R.S. Millikan from ionization potential and electron affinity.
(3) The electronegativity proposed by A.L. Alai is based on the electrostatic interaction between electrons of atomic nuclei and bonding atoms. When electronegativity values are used, they must be compared with the same set of values.
From left to right in the same period, the effective nuclear charge increases, the atomic radius decreases, the attraction to electrons becomes stronger, and the electronegativity value increases; From top to bottom, with the increase of atomic radius, the electronegativity of elements decreases. The electronegativity values of transition elements have no obvious regularity. Generally speaking, the electronegativity of typical nonmetallic elements in the upper right of the periodic table is larger, and that of fluorine is larger (4.0). The electronegativity values of metal elements in the lower left of the periodic table are very small, and cesium and francium are the elements with the lowest electronegativity (0.7). Generally speaking, the electronegativity of nonmetallic elements is greater than 2.0, and that of metallic elements is less than 2.0.
The concept of electronegativity can also be used to judge the positive and negative valence States of elements in compounds and the types of chemical bonds. Elements with large electronegativity often show negative valence when forming compounds because of their strong attraction to bonding electrons; However, those substances with less electronegativity show positive valence. When a covalent bond is formed, the shared electron pair is transferred to an atom with strong electronegativity, which makes the bond polar. The greater the difference in electronegativity, the stronger the polarity of the bond. When the electronegativity of the elements at both ends of the chemical bond is quite different (for example, greater than 1.7), the bond formed is mainly ionic bond.
Electronegativity of Common Elements (Pauling Scale)
Hydrogen 2. 1 lithium 0.98 beryllium 1.57 boron 2.04 carbon 2.55 nitrogen 3.04 oxygen 3.44 fluorine 3.98
Sodium 0.93 magnesium 1.3 1 aluminum 1 silicon 1.90 phosphorus 2. 19 sulfur 2.58 chlorine 3. 16.
Potassium 0.82 Ca1.00 Mn1.55 Fe1.83 Ni1.91Cu1.9zn1.65Ga/kloc-.
Rubidium 0.82 strontium 0.95 silver 1.93 iodine 2.66 barium 0.89 gold 2.54 lead 2.33
Generally speaking, those with electronegativity greater than 1.8 are nonmetallic elements, and those with electronegativity less than or equal to 1.8 are often metallic elements (of course, there are exceptions).