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## [[Covalent bond]]
- A covalent bond is a bond between two atoms means that those two atoms are sharing at least **one pair of [[Valence Electrons]] electrons**.
- It usually occurs between two **non metallic** elements.
- The reason why covalent bonds occur naturally in some elements is because the energy H of the system of bonded atoms is lower then the energy of those non-bonded elements.
> **Covalent bonds form what is known as a molecule.**
>[! Covalent bond image]
>![[Files/Covalent Bond img.png]]
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## [[Ionic Bond]]
- This is an when a difference in **charge** between two atoms causes them to bond due to an [[electrostatic force]].
- In an [[Ionic Bond]] an [[Electrons]] is transferred from one atom to another.
- Usually occurs between metallic atoms or **[[Ion]] with opposing charges**.
> **Ionic bonds form compounds.**
>[! Ionic bond image]
>![[Atomic Bonding.png]]
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## Reason for bonding
- Elements want to fill their [[Valence Electrons |Valence shell]] by bonding to other elements. Noble gasses already have a filled valence shell.
- Elements on the right of the periodic table have **too few** electrons in their valence shell and elements on the left side of the periodic table have **too many** electrons which is why they often bond with each other **covalently** to fill their [[Valence Electrons |Valence shell]].
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## Energy needed to break/form bonds
- The energy needed to break/form a bond is known as the **bond dissociation energy**.
- The bond dissociation energy **increases** towards the bottom left side of the periodic table because those elements have a **smaller atomic radius** and **a lower electron affinity**.
> [!tip]
> ##### General rule:
> - **The closer two atoms are in a bond the more energy it will take to break it.**
- The **more bonds** two atoms share *(double, triple)* the closer they are and thus the more energy it will take to break that bond.
### Finding the change in heat of a reaction (enthalpy)
- Add together the bond dissociation energies for all broken and formed bonds then subtract those two results to find the overall change in energy of a reaction.
- If the change in energy is **negative it is exothermic and endothermic otherwise**.
> [! Enthalpy equation example]
> <br>
>
> ![[Atomic bonding enthlypy.png]]
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## Effect of electronegativity
- The difference in **electronegativity** between two bonding atoms can be used to determine what kind of bond they have formed.
- The greater the difference the greater the **ionic character**.
> [! Electronegativity and bonds]
> <br>
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> - **NOTE:** In pure covalent bonds, the electrons are shared equally. In polar covalent bonds, the electrons are shared unequally.
> <br>
>
> - ![[Pasted image 20230120131418.png]]
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#mainpage