Overview
This lecture explains atomic structure by showing how atoms are built from protons, neutrons, and electrons, and introduces the concept of electron configuration using the first ten elements.
Atomic Structure Basics
- Atoms are made of three particles: protons (positive), neutrons (neutral), and electrons (negative).
- Protons and neutrons reside in the nucleus at the atom’s center; electrons move around the nucleus.
- Atoms are electrically neutral because they have equal numbers of protons and electrons.
Building Atoms
- Hydrogen (atomic number 1) has 1 proton and 1 electron.
- Helium (atomic number 2) requires 2 protons and 2 electrons; neutrons are needed to keep the positively charged protons together.
- The strong nuclear force acts in the nucleus to bind protons and neutrons.
Electron Shells and Configuration
- Electrons occupy shells around the nucleus; the first shell holds a maximum of 2 electrons, and the second shell holds up to 8.
- Lithium (atomic number 3): 3 protons, 3 electrons; electron configuration is 2 in the first shell, 1 in the second (2,1).
- Beryllium: 4 protons, configuration 2,2. Boron: 5 protons, configuration 2,3. Carbon: 6 protons, configuration 2,4.
- The atomic number equals the number of protons in an atom’s nucleus.
- The electron configuration affects chemical properties.
First Ten Elements' Electron Configurations
- Hydrogen: 1, Helium: 2, Lithium: 2,1, Beryllium: 2,2, Boron: 2,3, Carbon: 2,4, Nitrogen: 2,5, Oxygen: 2,6, Fluorine: 2,7, Neon: 2,8.
- A full second shell (8 electrons) makes neon a stable, unreactive noble gas.
Atomic Identity and Properties
- An atom's identity (element) is determined by its number of protons (atomic number).
- Electrons can be gained or lost, but the number of protons remains constant.
Key Terms & Definitions
- Proton — positively charged particle in the nucleus.
- Neutron — neutral particle in the nucleus.
- Electron — negatively charged particle orbiting the nucleus.
- Nucleus — center of the atom containing protons and neutrons.
- Atomic Number — number of protons in an atom, determines the element.
- Electron Configuration — distribution of electrons in an atom’s shells.
- Strong Nuclear Force — force holding protons and neutrons together in the nucleus.
Action Items / Next Steps
- Review the electron configurations of elements 1–10.
- Learn how electron configuration influences chemical reactivity.