Chapter 4: Atomic Structure Flashcards

Atomic Structure

• Atoms are the basic units of elements, retaining their identity during chemical reactions.

Historical Contributors

• Democritus: Proposed the concept of the atom as indivisible ('atomos'), favoring philosophical thought over experimental science.
• John Dalton: Developed the first atomic theory detailing the nature of atoms, emphasizing that elements consist of indivisible particles and combine in fixed ratios during chemical reactions.

Dalton's Atomic Theory

• All matter consists of tiny, indivisible particles called atoms.
• Atoms of identical elements are the same, but differ from atoms of other elements.
• Atoms can mix physically or chemically combine in simple whole-number ratios to form compounds.
• Chemical reactions involve the separation, joining, or rearrangement of atoms; atoms cannot change into different elements.

Techniques and Discoveries

• Scanning Tunneling Microscope: Allows visualization of individual atoms through graphical imaging.
• Subatomic Particles: Atoms are composed of protons (positively charged), neutrons (neutral), and electrons (negatively charged).
• J.J. Thomson: Identified electrons using a cathode-ray tube, proving their existence.
• Robert A. Millikan: Measured the charge and calculated the mass of the electron (1/1840 of a hydrogen atom).
• Eugen Goldstein: Discovered protons.
• James Chadwick: Discovered neutrons.

Atomic Models

• Thomson's Model: Known as the "plum-pudding model," which described electrons embedded in a positive charge.
• Ernest Rutherford: Conducted the gold-foil experiment, establishing the existence of a dense nucleus within atoms. His model depicted electrons orbiting a central nucleus containing protons and neutrons.

Atomic Composition

• Atomic Number: Number of protons in an atom, defining the element.
• Mass Number: Total number of protons and neutrons in an atom.
• Nuclide: Representation for an individual isotope.
• Atomic Mass: Weighted average of an element's isotopes.
• Isotopes: Variants of elements with the same number of protons but different numbers of neutrons.

Measurement and Classification

• Atomic Mass Unit (amu): A unit based on 1/12 of a Carbon-12 atom, used for measuring atomic masses.
• Periodic Table: Organized array of elements grouped by properties, reflecting periodic trends.
• Periods: Horizontal rows where element properties vary across the table.
• Groups/Families: Vertical columns indicating elements with similar properties.