Overview
This lecture introduces the basic concept of elements and atoms, describes atomic structure, and explains how atomic properties define elements and their behavior.
Substances and Properties
- Different substances have unique properties such as color, phase (solid, liquid, gas), and reactivity.
- Substances can change state with temperature: solids can melt to liquids or vaporize to gases.
- Observing materials led to questions about their most fundamental components.
Elements and the Periodic Table
- Elements are pure substances with specific properties that cannot be broken down chemically into simpler substances.
- Examples of elements: carbon, gold, lead; water is not an element but a compound (made of hydrogen and oxygen).
- All known elements are listed in the Periodic Table, identified by symbols (e.g., C for carbon, Au for gold).
Atoms: The Basic Unit
- The atom is the smallest unit of an element that retains its chemical properties.
- Atoms are incredibly small; about 1 million carbon atoms fit across the width of a human hair.
Atomic Structure
- Atoms consist of three main particles: protons (positive charge), neutrons (neutral), and electrons (negative charge).
- Protons and neutrons form the central nucleus, while electrons move around the nucleus.
- The number of protons (atomic number) defines which element an atom is.
- Changing the number of protons changes the element entirely (e.g., carbon vs. nitrogen).
Isotopes and Electrons
- Isotopes are variants of elements with the same number of protons but different numbers of neutrons (e.g., carbon-12 vs. carbon-14).
- Neutral atoms have equal numbers of protons and electrons; loss or gain of electrons results in ions with net charge.
Atomic Interactions
- Chemical reactions and bonding depend on how electrons interact between atoms.
- Atoms gain or lose electrons, forming charged ions, which affects their reactivity and bonding.
Key Terms & Definitions
- Element — A pure substance consisting of only one type of atom.
- Atom — The smallest unit of an element retaining its properties.
- Proton — Positive particle in the nucleus; defines the element.
- Neutron — Neutral particle in the nucleus; number can vary among isotopes.
- Electron — Negative particle moving around the nucleus.
- Atomic Number — Number of protons in an atom; determines the element.
- Isotope — Atoms of the same element with different numbers of neutrons.
- Ion — An atom or molecule with a net electric charge due to loss or gain of electrons.
Action Items / Next Steps
- Review the first 10 elements in the Periodic Table and their atomic numbers.
- Prepare to discuss how electron arrangements affect chemical bonding in the next class.