Chapter 2 Summary

1. Matter: Anything that occupies space and has mass, composed of atoms
2. Elements: Pure substances are composed of one type of atom; they cannot be broken down into simpler substances by chemical reactions
3. Compound: Molecules that contain more than one element in a fixed ratio
4. Atom: The smallest unit of matter that retains all of the chemical properties of an element
5. Protons: Positively charged particles found in an atom’s nucleus; determine an element’s identity
6. Electrons: Negatively charged particles orbiting around an atom’s nucleus; involved in chemical bonding and reactions
7. Neutrons: Particles with no charge found in the atom’s nucleus; contribute to the atom’s mass
8. Nucleus: Central region of an atom containing protons and neutrons; contains almost all of an atom’s mass
9. Atomic Number: The number of protons in the nucleus of an atom, unique for each element
10. Mass Number: The total number of protons and neutrons in an atom’s nucleus
11. Periodic Table of Elements: An organized chart listing all known elements, arranged by atomic number and chemical properties
12. Isotopes: Atoms of the same element with the same atomic number but different numbers of neutrons, resulting in different mass numbers
13. Radioactive Isotopes: Unstable isotopes that spontaneously emit radiation (particles and energy) to become more stable
14. Valence electrons: The electrons in an atom’s outermost energy shell; determines chemical reactivity and bonding
15. Valence number: The number of electrons required to fill the valence shell
16. Chemical Bonds: Forces holding atoms together through interactions involving electrons (ionic, covalent, and hydrogen bonds)
17. Octet Rule: Atoms tend to gain, lose, or share electrons to obtain eight electrons in their outermost energy level (stable configuration)
18. Ion: An atom or molecule with a positive or negative charge due to the gain or loss of electrons
19. Cations: Positively charged ions formed by the loss of electrons
20. Anions: Negatively charged ions formed by the gain of electrons
21. Electron Transfer: The movement of electrons from one atom to another, forming ions
22. Ionic Bond: Attraction formed when electrons are transferred from one atom to another, creating oppositely charged ions that attract each other
23. Covalent Bond: Chemical bond formed when atoms share pairs of electrons
24. Molecule: A group of two or more atoms held together by covalent bonds
25. Nonpolar Covalent Bonds: Covalent bonds where electrons are shared equally between atoms, creating no charge difference
26. Polar Covalent Bond: Covalent bond where electrons are shared unequally, creating slightly charged poles in the molecule
27. Hydrogen Bonds: Weak attractions between partially positive hydrogen atoms and partially negative atoms (e.g., oxygen or nitrogen)
28. Hydrophilic: Substances that easily interact or dissolve in water (“water-loving”)
29. Hydrophobic: Substances that repel or do not dissolve in water (“water-fearing”)
30. Temperature: A measure of the average kinetic energy (motion) of molecules in a substance
31. Evaporation: The transformation of liquid into vapour, usually involving energy absorption and cooling effects
32. Cohesion: Attraction between molecules of the same substance (e.g., water molecules sticking together)
33. Surface Tension: Cohesion at a liquid’s surface creating a “film” or resistance to external force
34. Adhesion: Attraction between different substances or molecules (e.g., water clinging to glass)
35. Solution: uniform mixture of liquid and substances dissolved in that liquid
36. Solvent: substance capable of dissolving another substance
37. Solute: substance dissolved in the solvent
38. Litmus Paper: Paper strips treated with dye that change colour in response to acidity or alkalinity
39. pH Scale: Numeric scale (0–14) measuring the acidity or alkalinity of a solution, where 7 is neutral, below 7 acidic, and above 7 basic
40. Acids: Substances releasing hydrogen ions (H⁺) in water, lowering pH (below 7)
41. Bases: Substances releasing hydroxide ions (OH⁻) or reducing hydrogen ions (H⁺), raising pH (above 7)
42. Buffers: Substances or systems that resist changes in pH by accepting or releasing hydrogen ions, maintaining a stable pH
43. 4 elements common to all living organisms: Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N)
44. 3 subatomic particles: protons (+), electrons (-), neutrons (o)
45. Structure of water: 2 hydrogen atoms and 1 oxygen atom, bonded via polar covalent bonds, resulting slight positive charge (δ+) on each hydrogen atom and a slight negative charge (δ-) on the oxygen atom
46. Properties of water: Water expands upon freezing, Water stabilizes temperature, Water is a versatile solvent, Water is cohesive
47. Polar Molecule: A molecule with a partial positive charge on one end and a partial negative charge on the other
48. Why is water cohesive? Hydrogen bonds between water molecules allow them to “stick” together
49. What is the biological significance of water being cohesive? It ensures bulk movement of water through living organisms (e.g. up a tree)
50. How does water stabilize temperature? To heat up, energy must be invested to break the hydrogen bonds that hold water molecules together before those water molecules can move freely. As water cools, the molecules slow their movement and energy is released as the hydrogen bonds between water molecules re-form.
51. What is the biological significance of water stabilizing temperatures? Water can absorb and release heat to ensure the temperature on Earth’s surface does not exceed a livable temperature.
52. Why does water expand upon freezing? Hydrogen bonds form between water molecules as it freezes, which creates a rigid, lattice-like structure that prevents water molecules from packing close.
53. What is the biological significance of ice being less dense than water? Ice will float on the water’s surface in lakes, ponds, and oceans, creating an insulating barrier to protect the animal and plant life beneath from freezing in the water.
54. Why is water a versatile solvent? Because water is polar, with slightly positive and negative charges, ionic compounds (such as salt) and polar molecules (such as sugar) can readily dissolve. The charged particles will form hydrogen bonds with a surrounding layer of water molecules.
55. What is the biological significance of water as a solvent? Water can dissolve substances to facilitate chemical reactions and transport of nutrients and waste within organisms (e.g. blood is mostly water)

OpenAI. (2025). ChatGPT. [Large language model]. https://chat.openai.com/chat
Prompt: Can you give me brief summaries of these key terms.