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Electronegativity Differences between atoms can be used to determine the type of bonding that occurs.
If the difference between 2 atoms is small (less than 1.7) the bond is covalent.
If the difference is large (greater than 1.7) the bond is considered ionic.
Exceptions- HF is covalent not ionic (difference of 1.9)
BF3 is covalent (difference of 2.0)
BeF2 is covalent (difference of 2.5)
Covalently bonded atoms will share their electrons in order to form a stable outer electron shell that has 8 electrons.
This is called an octet of electrons. (Hydrogen needs 2 electrons and forms a duet.)
Ionic is 1 minute in. Covalent is called "molecular" in this video.
Ionic bonded atoms will transfer one or more electrons from the less electronegative element (a metal) to the more electronegative element (a nonmetal) as to achieve an octect of electrons.
This results in the formation of 2 ions. One that is negatively charged (an anion) and one that is positively charged (a cation).
The bond is a strong electrostatic attraction formed by 2 opposing ions.