Quiz-style lecture reviewing basic atomic structure and related concepts.
Covers particle locations, charges, masses, forces in the atom, ions, and examples with aluminum.
Atomic Structure
Atom consists of nucleus (center) and electron cloud (outside).
Nucleus contains protons (positive) and neutrons (neutral).
Electrons (negative) orbit outside the nucleus and form the electron cloud.
Atoms are mostly empty space; nucleus is very small compared to electron cloud.
About 99% of an atom's mass is concentrated in the nucleus.
Key Particles, Charges, And Masses
Protons: carry +1 charge; located in nucleus.
Neutrons: electrically neutral (0 charge); located in nucleus.
Electrons: carry −1 charge; located outside nucleus in orbit/cloud.
Relative masses (SI units):
Proton: 1.672 × 10^−27 kg
Neutron: 1.6749 × 10^−27 kg (slightly heavier than proton)
Electron: 9.11 × 10^−31 kg (much lighter)
Relative masses (approx. atomic mass units):
Proton ≈ 1 amu
Neutron ≈ 1 amu
Electron ≈ 0.000549 amu
Atomic mass of an element is based on number of protons + neutrons; electron mass is negligible.
Forces And Electron Behavior
Opposite charges attract; like charges repel.
Electrostatic force attracts electrons toward nucleus.
Electrons remain in orbit due to their tangential velocity combined with electrostatic attraction.
If an electron gains enough energy (e.g., absorbs a photon), it can escape the atom → ionization (forms an ion).
Electron capture: an electron falls into the nucleus in certain nuclear reactions, changing the element.
Strong nuclear force (strong force) binds protons and neutrons in nucleus; much stronger than electrostatic repulsion, preventing protons from flying apart.
Ions And Charge Calculations
Net charge = (number of protons × +1) + (number of electrons × −1).
Example: Ion with 12 protons and 9 electrons → net charge = +12 + (−9) = +3.
Atoms under standard conditions are electrically neutral (equal protons and electrons).
Ions have unequal numbers of protons and electrons and therefore net positive or negative charge.
Positive ion = cation; negative ion = anion.
Example: Aluminum (Al)
Aluminum isotope example: Aluminum-27 (mass number 27, atomic number 13).
Atomic number (13) = number of protons.
Number of neutrons = mass number − atomic number = 27 − 13 = 14.
For neutral aluminum: electrons = atomic number = 13.
For Al^3+ ion: electrons = atomic number − charge = 13 − 3 = 10.
Neutral atoms are electrically neutral because protons = electrons.
Key Terms And Definitions
Nucleus: central region containing protons and neutrons.
Electron Cloud/Orbit: region where electrons move around nucleus.