Biology Chapter 2 & 3:

Atomic Structure and Electrons

• Electron Shells
  • Energy levels of electrons around an atom's nucleus.
  • Each shell is at a characteristic distance from the nucleus.
  • Outer shells contain more energy than inner shells.
  • Kinetic Energy for moving electrons.
  • Atoms with more electrons have additional electron shells.
  • The innermost shell can hold up to 2 electrons in 1 orbital.
  • The second shell has 4 orbitals capable of holding up to 8 electrons.

Atoms and Atomic Mass

• Atomic Mass is a measure of an atom's mass relative to other atoms, measured in Daltons (Da).
  • 1 Dalton = 1/12 the mass of a carbon atom.
  • Protons and Neutrons are found in the nucleus, while electrons are in shells.

Ions and Ionic Bonds

• Cations: Atoms with a net positive charge (lose electrons).
• Anions: Atoms with a net negative charge (gain electrons).
• Ionic Bonds: Formed when cations and anions bind via electrostatic attraction, typically between elements with different electronegativities.

Chemical Reactions

• Define as processes in which substances are transformed into new substances via bonds' formation or breaking.
  • Chemical reactions require energy (usually in the form of heat) and often need catalysts (e.g., enzymes).
  • Reactions tend toward equilibrium where forward and reverse reactions occur at equal rates.

Compounds and Covalent Bonds

• Compounds: Substances composed of two or more different elements; exhibit emergent properties differing from constituent elements (e.g., NaCl).
• Covalent Bonds: Strong bonds where atoms share electron pairs, leading to stable outer shells.
• Atoms typically aim for an octet of electrons (8 in the outer shell) to achieve stability.
  • The octet rule applies to elements like oxygen and nitrogen.

Moles and Isotopes

• 1 mole of any element contains Avogadro's number of atoms ($6.022 imes 10^{23}$).
• Isotopes: Atoms of the same element with varying neutron numbers.
• Radioisotopes: Unstable isotopes that decay over time.

Water Properties

• Water exists in three states: solid, liquid, and gas.
• Cohesion and adhesion are fundamental properties that impact water movement in plants.
• Heat capacity and specific heat are important properties of water affecting its thermal behavior.

Solutions and Concentrations

• A solvent is the medium in which solutes (e.g., dissolved substances) are mixed.
• Concentration measures the amount of solute in a given volume (e.g., molarity).

Biological Macromolecules

Proteins

• Proteins consist of amino acids and perform vital functions including:
  • Enzymatic: Catalyze reactions (e.g., hexokinase in glucose metabolism).
  • Structural: Provide support (e.g., collagen).
  • Transport: Move substances across membranes.
• Proteins are synthesized from amino acids via peptide bonds.

Nucleic Acids

• Nucleotides are the building blocks of DNA and RNA, essential for storing and transmitting genetic information.
• Structure differences: DNA has deoxyribose sugar; RNA has ribose.
• DNA: Stores genetic information; RNA: Transfers this information to synthesize proteins.