Estructura de lewis

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Writing Lewis Structures

Rules for writing structures
(1) you must know the order in which the atoms are connected This is normally determined by experiment and is referred to as theconstitution of a molecule General rule: the atom with the lowest electron affinity is usually the central atom

Levels of Structure
Elemental Composition Empirical Formula Molecular Formula ConstitutionConfiguration Conformation

Rules for writing structures
(1) you must know the order in which the atoms are connected
This is normally determined by experiment and is referred to as the constitutionof a molecule

Example: hypochlorous acid has the molecular formula HClO. But the atoms are connected in the order of HOCl

Rules for writing structures
(2)

Count the number of valenceelectrons

For main group elements this is the same as the group number in the periodic table Example: hypochlorous acid : HOCl H O Cl total 1 electron 6 electron 7 electron 14 valence electrons Rules for writing structures
(3)

write out the constitution in a form that shows the covalent bonds and count the number of electrons in covalent bonds
Example: hypochlorous acid H O Cl 4 electronsin covalent bonds 14 valence electrons 10 electrons remain to be assigned

Rules for writing structures
(4)

assign remaining electrons so as to complete the octets of as many atoms as possible.Example: hypochlorous acid HOCl

(4 electrons in covalent bonds + 10 more electrons assigned as shown) : H O : : : Cl :

Rules for writing structures
(5) when the number of electrons isinsufficient to complete the octetes of all of the atoms, assign them to atoms in order of decreasing atom electronegativity.
Example: nitrous acid H 18 valence electrons HNO2 : O : N : ( HONO ) : O: :Need to assign 12 electons in addition to 6 found in three bonds

Rules for writing structures
(6)

use unshared pairs for double bonds if this will satisfy octet rule.
Example: nitrous...
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