biochemistry

Atoms consist of a nucleus (protons and neutrons) with electrons surrounding it.
Ions are atoms with a net electrical charge; in solution, common example from salts: $Na^{+}$ and $Cl^{-}$ .
Hydrogen ion is $H^{+}$ ; acids increase $[H^{+}]$ in solution.

Ionic bond: electrostatic attraction between oppositely charged ions (often from electron transfer).
Covalent bond: sharing of electrons between atoms.
Nonpolar covalent bond: equal sharing of electrons (e.g., $H_{2}$ ).
Polar covalent bond: unequal sharing leading to partial charges.

Water requires energy to change phase: ice -> liquid, liquid -> steam.
Water as solvent: solvent is $H_{2}O$ ; solute (e.g., sugar) dissolves to form a solution.
Solution: homogeneous mixture of solute and solvent.
Cohesion: water molecules stick to each other.
Adhesion: water sticks to surfaces (e.g., skin);
Surface tension: water has high surface tension, can act like a skin on its surface.
Capillary action: water moves through narrow spaces (e.g., in wood) due to cohesive and adhesive forces.
Density: ice is less dense than liquid water; ice floats on water.

Solvent: the substance doing the dissolving (water, in most biological contexts).
Solute: the substance being dissolved (e.g., sugar).
Solution: dissolved homogeneous mixture of solute in solvent.

Increase in $H^{+}$ ions indicates higher acidity (lower pH).
$H^{+}$ represents a positively charged hydrogen ion; neutral diatomic hydrogen $H_{2}$ has no charge.

High salt intake is associated with hypertension; reducing salt can help manage blood pressure.