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chem: dipoles and polarity

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@ -711,6 +711,30 @@ In a trigonal bipyramidal, the **equatorial** positions of domains refer to the
$\text{AX}_4\text{E}_2$:
<img src="/resources/images/vsepr-ax4e2.png" width=700></img>
### Molecular polarity
The polarity of a molecule refers to how even the distribution of electrons **overall** throughout the molecule (not to be confused with the electron distribution in VSEPR) and affects only the physical properties of the compound.
The polarity of a molecule depends on the presence of polar bonds and the molecular shape of the molecule. In this course, if a molecule is **symmetrical** in three dimensions or does not contain any polar covalent bonds, it is non-polar. The shape of the molecule affects the directions that dipoles act in in their three-dimensional forms and can cause dipoles to cancel out.
!!! definition
The **net dipole moment** of a molecule is the vector sum of all bond dipoles in a molecule. Only polar molecules have net dipole moments.
Bond dipoles can be represented as vectors pointing in the direction of the atom with greater electronegativity with one line across it.
!!! example
<img src="/resources/images/equal-dipoles.png" width=700>(Source: Kognity)</img>
Generally, tetrahedral and trigonal planar molecules with the same atoms bonding to the central atom are non-polar molecules as their bond dipoles cancel out. Trigonal pyramidal and linear diatomic molecules with polar bonds typically are polar because their bond dipoles do not cancel each other out.
!!! example
<img src="/resources/images/uneven-dipoles.png" width=700>(Source: Kognity)</img>
By convention and missing in the examples above, the lowercase delta ($\delta$) is used to indicate polarity. The less electronegative atom/side of a molecule is marked as $\delta^+$ while the atom/side where electrons spend more time around on average is labelled $\delta^-$, indicating **partial** positive/negative charges, respectively.
!!! example
<img src="/resources/images/dipole-sign.png" width=300>(Source: Kognity)</img>
## 4.4 - Intermolecular forces
## 4.5 - Metallic bonding