Overview
This lecture explains atomic structure, focusing on protons, neutrons, and electrons, how to find their numbers in atoms and ions, and the concept of isotopes and average atomic mass.
Atomic Structure Basics
- Atoms are made of protons and neutrons (in the nucleus) and electrons (in energy levels around the nucleus).
- Protons have a positive charge, electrons have a negative charge, and neutrons are neutral.
- Atomic number equals the number of protons; in a neutral atom, protons = electrons.
- Electrons in the outermost energy level are called valence electrons.
- Core electrons are the inner electrons closest to the nucleus.
Periodic Table Relationships
- Group number often indicates number of valence electrons (e.g., Group 1A: 1 valence electron).
- Atomic number is the smaller number on the element symbol; mass number (or average atomic mass) is the larger.
Ions and Isotopes
- Ions are charged atoms: cations have fewer electrons than protons (positive charge); anions have more electrons than protons (negative charge).
- Number of protons identifies the element; neutrons = mass number – atomic number.
- Electrons in ions = atomic number – charge (subtract for cations, add for anions).
- Isotopes are atoms of the same element with different numbers of neutrons and different mass numbers but same chemical behavior.
Atomic Forces
- Opposite charges attract, like charges repel; the strong nuclear force holds the nucleus together despite repulsion between protons.
Calculating Average Atomic Mass
- Average atomic mass is a weighted average of all natural isotopes, reflecting their relative abundances.
- Formula: (isotope mass × relative abundance) + (other isotope mass × relative abundance), etc.
- Example: For boron: 10×0.19 + 11×0.81 = 10.81
Determining Isotope Abundance
- If average atomic mass is closer to one isotope’s mass, that isotope is more abundant.
- To solve for unknown abundance: use variables (x and 1–x) and set up an equation based on the average atomic mass.
Key Terms & Definitions
- Atom — smallest unit of matter with protons, neutrons, and electrons.
- Proton — positively charged particle in the nucleus.
- Neutron — neutral particle in the nucleus.
- Electron — negatively charged particle surrounding the nucleus.
- Valence electrons — electrons in the outermost energy level.
- Isotope — atoms of the same element with different numbers of neutrons.
- Ion — atom with unequal protons and electrons; can be cation (+) or anion (–).
- Average atomic mass — weighted mean of all the isotopes' masses for an element.
Action Items / Next Steps
- Practice calculating number of protons, neutrons, and electrons for given atoms and ions.
- Calculate average atomic mass and percent abundance for isotopes using provided formulas.
- Review periodic table groupings and their relation to valence electrons.