chem: add bonding intro

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eggy 2020-10-05 21:25:02 -04:00
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## 4.0 - Chemical bonding and structure
A chemical bond consists of the strong electronic interactions of the **valence** electrons between atoms that hold the atoms closer together. This only occurs if the atoms would reduce their potential energy by bonding.
!!! reminder
- Metal + metal = metallic bond
- Metal + non-metal = ionic bond
- Non-metal + non-metal = covalent bond
### Percentage ionic character
Bonding is a spectrum. The percentage ionic character of a chemical bond shows roughly the amount of time valence electrons spend near an atom or ion in a bond. The difference between two elements' electronegativity (ΔEN) indicates how covalent and how ionic the bond **behaves**.
If ΔEN is:
- less than 0.5, it behaves like a **pure covalent** bond
- between 0.5 and 1.7, it behaves like a **polar covalent** bond
- greater than 1.7, it behaves like an **ionic** bond
## 4.1 - Ionic bonding and structure
Ionic bonds are the interaction of **oppositely charged ions**. Electrons are transferred first, and then the bond forms via the attraction of the now-positive and negative ions. This reduces the potential energy of the ions and therefore increases their stability.
!!! warning
When expressing ionic bonds in a Lewis dot diagram, the oppositely-charged ions must *never* be placed next to one another.
## 4.2 - Covalent bonding