[[Chemistry of Life]]

# SUMMARY
## Key Takeaways

- Water is polar because the O-H bonds are polar covalent, giving oxygen a partial negative charge and each hydrogen a partial positive charge.
- Hydrogen bonds form between the partial positive hydrogen of one water molecule and the partial negative oxygen of a neighboring molecule.
- Hydrogen bonding produces cohesion, adhesion, and surface tension between water molecules.
- Water's high specific heat capacity helps organisms maintain a stable, homeostatic body temperature.
- Water's high heat of vaporization allows [evaporative cooling](https://fiveable.me/ap-bio/key-terms/evaporative-cooling), which also helps maintain body temperature.
- Hydrophilic substances attract water; [hydrophobic](https://fiveable.me/ap-bio/key-terms/hydrophobic) substances do not, because polarity determines what mixes with water.

| Term                   | Definition                                                                                                                                                           |
| ---------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| adhesion               | The attractive force between water molecules and other polar substances, allowing water to stick to different surfaces.                                              |
| cohesion               | The attractive force between water molecules that causes them to stick together, resulting from hydrogen bonding.                                                    |
| evaporative cooling    | The process by which the evaporation of water removes heat from an organism or environment.                                                                          |
| heat of vaporization   | The energy required to convert a liquid to a gas, enabling water to remove heat from organisms through evaporative cooling.                                          |
| homeostasis            | The maintenance of stable internal environmental conditions in an organism despite external and internal changes.                                                    |
| hydrogen bond          | Weak attractive forces between a hydrogen atom bonded to an electronegative atom and another electronegative atom, occurring between or within biological molecules. |
| polar covalent bonds   | Chemical bonds between atoms where electrons are unequally shared, resulting in partial positive and negative charges.                                               |
| polarity               | The unequal distribution of electrical charge in a molecule, resulting in one end being partially positive and the other partially negative.                         |
| specific heat capacity | The amount of energy required to raise the temperature of a substance by one degree, allowing water to resist rapid temperature changes.                             |
| surface tension        | The property of water that allows its surface to resist breaking, resulting from hydrogen bonding between adjacent water molecules.                                  |

# Overview
covalents are 0-0.5 difference in electronegativities
polar covalents are 0.5 - 2
Ionics are 2+
			
hydrogen bonds are when a hydrogen atom in one molecule is highly attracted to an atom with high electronegativity in another molecule.
hydrogen bonds are rather weak, water uses hydrogen bonds

**properties of water:**
1. cohesion
2. adhesion
3. high heat capacity
4. high surface tension

adhesion is a result of the polarity, as the imbalance of charge allows the molecules to bind to other things easily

high heat capacity results from heat energy being used to break and disrupt the hydrogen bonds, inadvertently losing some of the heat

surface tension results from hydrogen bonds

**ph**
ph measures how acidic or basic a solution is
![[Pasted image 20260810212842.png]]"**==Acids==** donate protons (Hydrogens) to **==bases==**, which are hydrogen/proton acceptors. Let’s use the self ionization of water pictured above as an example. One of the water molecules is acting as an acid and donating an H+ ion (proton) to the other water molecule, which is the base. This forms a hydronium ion (H3​O+) and a hydroxide ion (OH−)."

solutions with more hydroniums than hydroxides are acidic, and the other way
![[Pasted image 20260810213049.png]]
$pH=-\log[H^+]$
where $H^+$ is the hydronium concentration in the solution

pH has an opposite, pOH
by definition the pH + pOH of a solution will always equal 14