lewis theory

# Difference in electronegativity and the electron is

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difference in electronegativity and the electron is almost completely transferred to the nonmetal, and the bond is ionic e.g. NaCl if there is an intermediate electronegativity difference such as between two nonmetals, then the bond is polar covalent e.g. HCl

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we can quantify the polarity of a bond by the size of its dipole moment a occurs when there's a separation of positive and negative charge the magnitude of a dipole moment created by separating two particles of equal but opposite charge of magnitude q by a distance of r is given by: the debye (D) is the common unit for a dipole moment the percent ionic character is defined as the ratio of a bond's actual dipole moment to the dipole moment it would have if the electron were completely transferred from one atom to another, multiplied by 100% a bond with complete transfer of an electron is known to have 100% ionic character (even the most ionic bonds do not reach this ideal) as expected as electronegativity difference increases so does the percent ionic character , no bond is 100% ionic so any bond with greater than 50% ionic character is referred to as an ionic bond How to write a lewis structure: 1. write the correct skeletal formula for the structure the atoms must be in the same positions that they would be in nature e.g. for water, HHO would be incorrect, HOH would be correct hydrogen atoms are always terminal - on the end of the molecule central atoms must always have at least two bonds, which is why hydrogen is never a central atom always put the more electronegative atoms on the terminal ends use formal charge to determine between competing Lewis structures 2. determine the total number of electrons for the Lewis structure by summing the valence
electrons of each atom in the molecule number of valence electrons for main group elements is its group number when writing Lewis structures for molecules containing polyatomic ions, remember to take this into consideration when determining the total number of electrons - add one electron for every negative charge, and remove one electron for every positive charge the atom that loses/gains an electron is not important, only the total number of electrons is important 3. distribute electrons among the atoms, giving octects (or duets for hydrogen) to as many atoms as possible, if single bonds don't fulfill obtaining an octet, use double or triple bonds Resonance occurs when there are two or more valid Lewis structures for the same molecule in nature the molecule tends to exist as an average of the two possible Lewis structures e.g. O3 has two possible resonance structures each containing one single bond and one double bond yet we find that, in nature, both bonds are intermediate between single and double bonds, both in length and in strength to account for these different representations of the same molecule we draw all possible types of Lewis structures with double-headed arrows between them - known as

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