βοΈ Atoms & Molecules
- States of matter β solid, liquid, gas phase changes
- Describe atomic structure using protons, neutrons, and electrons
- Read element symbols and match them to names and atomic numbers
- Explain ion formation through electron gain or loss
- Interpret chemical formulas and count atoms in a compound
An atom is like a miniature solar system with the nucleus at the center and electrons orbiting around it. Here is the mind-blowing part: 99.9999 percent of an atom is empty space! Matter feels solid because of electromagnetic repulsion between electrons, not because atoms are packed tightly.
Atoms are the fundamental building blocks of all matter. Understanding why salt dissolves in water, why iron rusts, or how a lithium battery stores energy all begins at the atomic level. Modern industries β semiconductors, pharmaceuticals, batteries, synthetic materials β are built on precise manipulation of atoms and molecules. The language of chemical formulas is the starting point for all of chemistry, biology, and materials science.
- Atom structure: nucleus (protons + neutrons) + electrons. Atomic number = protons = electrons
- Mass number = protons + neutrons. Isotopes: same atomic number, different mass
- Ions: lose electrons β cation (+), gain electrons β anion (β)
- Molecules: neutral particles formed by covalent bonding. Written as chemical formulas
- Periodic table: arranged by atomic number. Same group = similar chemical properties
1. Atomic Structure
- Nucleus: Contains protons (+) and neutrons (neutral). Holds almost all the atom's mass.
- Electrons (β): Orbit the nucleus in electron shells. Very low mass.
- Atomic number = number of protons = number of electrons (in a neutral atom)
- Mass number = protons + neutrons
2. Element Symbols & the Periodic Table AP Exam
| Element | Symbol | Atomic # |
|---|---|---|
| Hydrogen | H | 1 |
| Carbon | C | 6 |
| Nitrogen | N | 7 |
| Oxygen | O | 8 |
| Sodium | Na | 11 |
| Chlorine | Cl | 17 |
| Calcium | Ca | 20 |
| Iron | Fe | 26 |
Periodic Table patterns: Elements in the same group (column) share similar chemical properties. Period 1 = noble gases (He, Ne, Arβ¦) in Group 18.
3. Ions
- Cation (+): Lost electrons β positive charge. Example: Na β NaβΊ, Ca β CaΒ²βΊ
- Anion (β): Gained electrons β negative charge. Example: Cl β Clβ», O β OΒ²β»
- Ionic bond: Attraction between a cation and an anion (e.g., NaCl = table salt)
4. Molecules & Chemical Formulas AP Exam
- Water: HβO β 2 hydrogen + 1 oxygen
- Carbon dioxide: COβ β 1 carbon + 2 oxygen
- Ammonia: NHβ β 1 nitrogen + 3 hydrogen
- Glucose: CβHββOβ β 6C, 12H, 6O
- Oxygen gas: Oβ β a diatomic molecule (two oxygen atoms bonded)
Subscripts show the number of atoms of each element in one molecule.
Practice Questions
Answer: Protons = 11, Neutrons = 23 β 11 = 12, Electrons = 11. This is sodium (Na).
Answer: Na is a neutral sodium atom (11p, 11e). NaβΊ is a sodium ion that lost one electron (11p, 10e), giving it a +1 charge.
- Atomic structure: protons(+) + neutrons = nucleus / electrons(β) = orbitals
- Atomic number = number of protons = number of electrons (neutral atom)
- Ions: lose electrons β cation(+) / gain electrons β anion(β)
- Ionic bonds (metal+nonmetal) vs covalent bonds (nonmetal+nonmetal)
Review this material at increasing intervals to commit it to long-term memory.