We explain what is valence in chemistry and what are the types of valence that exist. In addition, examples of some chemical elements.
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What is valence?
In chemistry, we speak of valence to refer to the number of electrons that an atom of a given element has in its last level of energy , that is, in its outermost orbit. These electrons are of special relevance because they are responsible for the covalent bonds (co-valent: they share valence) and they intervene when it comes to chemical reactions.
An atom can have one or more valences , however, and for this reason this concept, created in the nineteenth century to explain the “affinities” between the different atoms that were known, has been replaced with the “oxidation number”, That finally represents the same.
Thus, for example, the hydrogen atom has a valence of 1, which means that it can share an electron in its last layer; carbon, on the other hand, has a valence of 2 or 4 , that is, it can offer two or four electrons. Hence the valence number represents the ability of the element to gain or transfer electrons during a reaction or chemical bond .
Throughout history, the concept of Valencia allowed the development of theories regarding chemical junctions , such as Lewis’s structure in 1916, the theory of the Valencia bond in 1927, the theory of molecular orbitals in 1928, the theory of repulsion of electronic pairs of the valence layer in 1958 and different theories of quantum physics.
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Types of Valencia
There are two different types of valence, which are:
- Maximum positive Valencia . It reflects the maximum combinatorial capacity of an atom, that is, the greatest amount of electrons it can give. Electrons have a negative charge, so an atom that gives them gets a positive valence (+).
- Valencia negative . It represents the ability of an atom to combine with another that has a positive valence. Atoms that receive electrons have a negative valence (-).
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Valencia of the elements
The known valences of the main elements of the periodic table are the following:
- Hydrogen (H): 1
- Carbon (C): 2, 4
- Sodium (Na): 1
- Potassium (K): 1
- Aluminum (Al): 3
- Mercury (Hg): 1, 2
- Calcium (Ca): 2
- Iron (Fe): 2, 3
- Lead (Pb) : 2, 4
- Chrome (Cr): 2, 3, 6
- Manganese (Mn): 2, 3, 4, 6, 7
- Chlorine (Cl): 1, 3, 5, 7
- Oxygen (O): 2
- Sulfur (S): 2, 4, 6
- Nitrogen (N): 3, 5
- Arsenic (As): 3, 5
- Boron (B): 3
- Silicon (Yes): 4
- Gold (Au): 1, 3
- Silver (Ag): 1
- Phosphorus (P): 3, 5
- Radius (Ra): 2
- Magnesium (Mg): 2
- Copper (Cu) : 1, 2
