Chemistry 1

Atomic Number: Each element has a unique atomic number that indicates the number of protons in the nucleus.
- Example: Oxygen (O) has an atomic number of 8, meaning oxygen atoms contain 8 protons.
Atomic mass: Calculated as the total number of protons plus neutrons.
- Oxygen has 8 protons and 8 neutrons, giving it an atomic mass of 16 (rounded).
Electrons: For neutral atoms, the number of electrons equals the number of protons. Thus, oxygen has 8 electrons in its neutral state.

Isotopes: Variants of an element that have the same number of protons but different numbers of neutrons.
- Example: Hydrogen (H) has isotopes like protium (1 proton, 0 neutrons), deuterium (1 proton, 1 neutron), and tritium (1 proton, 2 neutrons).
Radioactivity: Certain isotopes, like tritium, have excess energy and can release radiation.
Applications: Isotopes are used in medical imaging and treatment. For instance, some isotopes can be utilized in PET scans to visualize internal structures non-invasively.

Electron Orbitals: Regions around an atom's nucleus where electrons can be found, with rules governing the distribution of electrons across these orbitals.
- The octet rule: Atoms tend to fill their outermost electron shells. The first shell holds a maximum of 2 electrons; subsequent shells can hold up to 8.
Valence Shell: The outermost electron shell which determines an atom's bonding behavior.
- Atoms with full valence shells (noble gases) are chemically inert; those with incomplete shells tend to bond.

Ionic Bonds: Formed when atoms transfer electrons.
- Example: Sodium (Na) loses 1 electron to chlorine (Cl), forming NaCl (table salt).
Covalent Bonds: Formed when atoms share electrons.
- Example: Water (H2O) has two hydrogen atoms sharing electrons with one oxygen atom, creating polar covalent bonds due to differences in electronegativity.
Polar vs. Non-Polar Covalent Bonds: Polar bonds have unequal sharing of electrons (e.g., water) while non-polar bonds share electrons equally (e.g., CH4).
Hydrogen Bonds: Weak interactions between polar molecules, crucial for the properties of water, such as surface tension and high heat capacity.

Cohesion and Adhesion: Water molecules tend to stick together (cohesion) and to other substances (adhesion) due to hydrogen bonding, crucial for processes like capillary action.
High Heat Capacity: Water can absorb a lot of heat before it begins to change temperature, aiding in temperature regulation in organisms.
Unique Density Behavior: Ice is less dense than liquid water, allowing it to float and providing insulation in aquatic environments.

Overview of reaction types:
- Synthesis Reactions: Combine smaller molecules to create larger ones.
- Decomposition Reactions: Break down larger molecules into smaller units.
- Exchange Reactions: Involve the swapping of components between molecules.
- Reversible Reactions: Can proceed in both directions.
Dehydration Synthesis: A form of synthesis where water is removed to bond molecules together (e.g., forming proteins from amino acids).
Hydrolysis: A type of decomposition involving water to break down compounds (e.g., breaking down polysaccharides into monosaccharides).

pH Scale: Ranges from 0 to 14; a measure of hydrogen ion concentration in a solution.
- 7 is neutral; below 7 is acidic, above 7 is basic/alkaline.
Buffer Systems: Maintain pH stability in biological systems.
- Example: The bicarbonate buffering system helps stabilize blood pH around 7.35 to 7.45 by converting carbonic acid to bicarbonate and vice versa, depending on hydrogen ion concentration.

Isotopes offer valuable tools in diagnostics and treatment. For example, radioactive isotopes can help visualize metabolic processes using techniques like PET scans.