General Biology: Chemistry Foundations Study Guide

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Matter is anything that has mass and occupies space. Understanding its phases is essential for grasping biological and chemical processes.

Definition: Matter exists in different phases: solid, liquid, and gas.
Phase Transitions: Changes between phases depend on energy input (e.g., heating/cooling).
Examples: Water transitions: ice (solid), liquid water, water vapor (gas), and carbon dioxide (CO2).

Atoms are the basic units of matter, elements are pure substances of one type of atom, and molecules are combinations of atoms bonded together.

Atom: Smallest unit of matter retaining element properties. Composed of protons, neutrons, and electrons.
Element: Pure substance of one atom type. Examples: H (Hydrogen), Fe (Iron), Al (Aluminum).
Molecule: Two or more atoms bonded together. Examples: H2O (water), NaCl (salt), CH4 (methane).
CHNOPS Elements: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur—essential for life.
Trace Elements: Required in small amounts (e.g., Fe, Zn).

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells.

Proton (p+): Positively charged, in nucleus. Number of protons = atomic number (Z).
Neutron (n0): Neutral, in nucleus. Number of neutrons + protons = mass number (A).
Electron (e-): Negatively charged, orbits nucleus.
Isotope: Atoms of the same element (same Z) but different numbers of neutrons (different A).
Ion: Atom or molecule that has gained or lost electrons.

The periodic table organizes elements by atomic number and electron configuration, revealing chemical properties and trends.

CHNOPS elements are the most abundant in living organisms and form the backbone of biomolecules.

Electron shells determine chemical reactivity and bonding. Valence electrons are those in the outermost shell.

Valence: Number of electrons in outer shell.
Stability: Atoms with full outer shells (2 or 8 electrons) are stable (noble gases).
Bond Formation: Atoms with incomplete valence shells form chemical bonds.
Maximum electrons per shell: First shell holds 2, second shell holds 8.

Chemical bonds hold atoms together in molecules. The type of bond affects molecular properties.

Ionic Bonds: Transfer of electrons between atoms, forming cations (+) and anions (−). Example: NaCl.
Covalent Bonds: Sharing of electrons between atoms. Example: H2O, O2.
Hydrogen Bonds: Weak attraction between polar molecules, important in water, DNA, and proteins.

Water's unique properties are vital for life, due to its molecular structure and hydrogen bonding.

Composition: 2H2 + O2 → 2H2O.
Polarity: Oxygen is more electronegative, creating a partial negative charge; hydrogen is partially positive.
Hydrogen Bonding: Each H2O can bond with 4 neighbors.

High Heat Capacity: Resists temperature changes; important for homeostasis.
High Heat of Evaporation: Cooling effect; sweating cools the body.
Solvent Properties: Dissolves polar/ionic compounds (hydrophilic), not nonpolar (hydrophobic).
Cohesion: Water molecules stick together (surface tension).
Adhesion: Water sticks to other polar surfaces (e.g., glass, paper).
Density: Ice is less dense than liquid water, allowing it to float and insulate aquatic life.

Acids and bases affect biological systems by altering pH, which measures hydrogen ion concentration.

Acid: Donates H+ ions. Example: HCl.
Base: Accepts H+ ions or releases OH- ions. Example: NaOH.
pH Scale: Measures H+ concentration.
Buffer: System that stabilizes pH by resisting drastic changes (e.g., carbonic acid-bicarbonate system in blood).

Bond Type	Description	Example
Ionic Bond	Transfer of electrons between atoms	NaCl
Covalent Bond	Sharing of electrons between atoms	H2O, O2
Hydrogen Bond	Weak attraction between polar molecules	Between H2O molecules

Property	Description
High Heat Capacity	Resists temperature change
High Heat of Evaporation	Cooling effect (e.g., sweating)
Cohesion	Water molecules stick together
Adhesion	Water sticks to other polar surfaces
Density	Ice is less dense than liquid water

Electronegativity is the tendency of an atom to attract electrons in a covalent bond, leading to polarity in molecules.
Polarity in water enables hydrogen bonding, which is crucial for the structure of proteins and nucleic acids.
CHNOPS elements are fundamental for the structure and function of biomolecules such as carbohydrates, lipids, proteins, and nucleic acids.