Chemical Basis for Life

Elements and Compounds:
- Element: Basic substance that cannot be broken down.
- Compound: Substance formed from elements chemically combined, e.g., sodium chloride (NaCl).

Atoms and Subatomic Particles:
- Atoms consist of protons (+), neutrons (neutral), and electrons (-).
- Atomic number = # of protons.
- Atomic mass = # protons + # neutrons.
Isotopes:
- Same protons, different neutrons.
- Radioactive isotopes decay and emit radiation (e.g., Carbon-14, Fluorine-18).
Chemical Bonds:
- Reactivity of atoms based on filling outermost (valence) shell.
- Covalent bonds involve sharing of electron pairs (strong bonds).
- Determining number of bonds necessary for elements like O, C, N.
Polar Covalent Bonds:
- Formed when electrons are shared unequally due to electronegativity differences leading to polar molecules.
Ionic Bonds:
- Occur when atoms strip electrons and form charged ions.
- Oppositely charged ions attract and create ionic compounds.
Weak Chemical Bonds:
- Hydrogen bonds and van der Waals interactions crucial for biological structures.
Chemical Reactions:
- Involve rearrangement of atoms, making or breaking bonds, can release/store energy.
- Example: Photosynthesis - Reactants (CO2, H2O) produce Glucose (C6H12O6) and O2.
Reversible Reactions:
- Indicated by double arrows; reactions can proceed in either direction (e.g., condensation and hydrolysis).