Chemistry of Life and Atomic Structure

Study Notes

25 elements are essential for life
Four elements make up 96% of living matter: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N)
Four elements make up most of the remaining 4%: Phosphorus (P), Calcium (Ca), Sulfur (S), and Potassium (K)

Atoms are the basic building blocks of matter
The outermost shell of an atom, the valence shell, determines its chemical behavior
Electrons fill shells from the inside out: 1st shell holds 2 electrons, 2nd shell holds 8, and 3rd shell holds 8
Elements in the same row of the periodic table have the same number of shells
Elements in the same column have the same number of valence electrons and similar chemical properties

Covalent bonds: Two atoms share a pair of electrons, forming molecules
Hydrogen bonds: Weak attractions between polar molecules, like water molecules, due to the attraction of a positive hydrogen atom to a negative oxygen atom
Ionic bonds: Transfer of electrons from one atom to another, creating ions

Water is essential for all life, existing both inside and outside cells
Cohesion: Water molecules are attracted to each other due to hydrogen bonding, leading to surface tension and capillary action
Adhesion: Water molecules are attracted to other substances, also due to hydrogen bonding.
Solvent: Water is a good solvent for many molecules, due to its polarity.
Lower density as a solid: Ice floats because it's less dense than liquid water
High specific heat: Water can absorb a lot of heat before its temperature changes significantly
High heat of vaporization: Water requires a lot of energy to evaporate

Hydrophilic: Substances that are attracted to water, often polar molecules
Hydrophobic: Substances that are not attracted to water, often non-polar molecules

pH scale: Measures the acidity or alkalinity of a solution, ranging from 0 to 14
Acid: A substance that releases hydrogen ions (H+)
Base: A substance that accepts hydrogen ions
Buffer: A solution that resists changes in pH