Overview
This lecture reviews basic atomic structure, isotopes, subatomic particles, and introduces scientific models of the atom.
Atomic Structure Basics
- The atomic number equals the number of protons in an atom.
- Atoms are electrically neutral, so protons = electrons.
- The mass number is the total number of protons and neutrons in the nucleus.
- The number of neutrons is found by subtracting the atomic number from the mass number.
Isotopes
- Isotopes have the same number of protons and electrons but different numbers of neutrons.
- All carbon atoms have 6 protons and 6 electrons, but carbon-12 has 6 neutrons, carbon-13 has 7, and carbon-14 has 8.
Subatomic Particles
- Three subatomic particles: proton (positive), electron (negative), neutron (neutral).
- Evidence for electrons comes from Thompson's experiments showing all atoms produce the same results in cathode ray experiments, regardless of the material.
- Neutrons were discovered last (in 1932) because they are neutral and not affected by electric or magnetic fields; they are slightly heavier than protons.
Scientific Models
- A scientific model can be a drawing, diagram, graph, or equation, used to represent and predict phenomena.
- Models are used to make testable, quantifiable predictions and help us understand atomic structure.
- The accepted atomic model: a small nucleus (protons and neutrons) at the center, surrounded by a cloud of electrons.
Atomic and Molecular Models
- An atom of an element: a single sphere.
- A molecule of an element: two or more identical spheres joined together.
- A molecule of a compound: two or more different types of spheres joined together.
- An "atom of a compound" is not possible; a compound must have more than one atom.
Key Terms & Definitions
- Atomic Number — number of protons in an atom.
- Mass Number — total number of protons and neutrons.
- Isotope — atoms with same protons and electrons but different neutrons.
- Proton — positively charged subatomic particle.
- Electron — negatively charged subatomic particle.
- Neutron — neutral subatomic particle.
- Scientific Model — representation (physical or conceptual) that explains and predicts scientific phenomena.
- Element — substance with atoms of the same type.
- Compound — substance with atoms of different types chemically bonded.
- Molecule — two or more atoms bonded together.
Action Items / Next Steps
- Review definitions and distinctions among atoms, molecules, elements, and compounds.
- Practice identifying types of particles and isotopes using atomic and mass numbers.