Atomic Structure and Notable Experiments

Atomic Structure

• Atoms are the fundamental units of matter, made up of subatomic particles.
• Subatomic particles include protons, neutrons, and electrons, with protons and neutrons located in the nucleus and electrons orbiting around it.
• Charged particles behave according to electromagnetic principles: like charges repel and opposite charges attract.

Notable Experiments

• Thomson's cathode ray experiments revealed the electron, establishing its charge-to-mass ratio.
• Millikan's oil-drop experiment quantified the charge of the electron.
• Becquerel discovered radioactivity, confirming atomic substructure.
• Rutherford's gold foil experiment led to the nuclear model, highlighting a dense, positively charged nucleus.

Atomic Characteristics

• Electronic charge, denoted as e, is the charge magnitude of an electron, with protons having an equal but positive charge.
• Atomic mass is measured in atomic mass units (amu); common dimension is angstroms for atomic sizes.
• Atomic number defines an element’s identity, representing the number of protons in the nucleus.
• Mass number equals the total number of protons and neutrons; isotopes are variants of an element differing in mass number.

Atomic Mass and Weight

• The atomic mass scale is anchored by assigning 12 amu to carbon-12.
• Atomic weight—the average mass of an element—is derived from isotope masses and abundances.
• Mass spectrometry is a primary method for accurately measuring atomic and molecular weights.

The Periodic Table

• The periodic table organizes elements by atomic number, grouping elements with similar properties in vertical columns (groups) and horizontal rows (periods).
• Metals occupy the left and central areas, with nonmetals on the upper right; metalloids are found along the dividing line between metals and nonmetals.

Molecular Compounds

• Atoms can combine to create molecules; molecular compounds typically consist solely of nonmetals.
• Diatomic molecules contain two atoms, and the substance's composition is described by its chemical formula.
• Empirical formulas indicate relative atom numbers; molecular formulas show exact quantities, while structural formulas depict atom connectivity.

Ions and Ionic Compounds

• Atoms can lose or gain electrons, forming ions: metals form cations (positively charged), while nonmetals form anions (negatively charged).
• Ionic compounds consist of cations and anions, remaining electrically neutral overall, often containing both metal and nonmetal elements.
• Polyatomic ions are charged groups of covalently bonded atoms, and chemical formulas for ionic compounds are written based on ion charges.

Chemical Nomenclature

• The systematic naming rules for ionic compounds require naming cations first, followed by anions, with additional considerations for multiple metal ion charges using Roman numerals.
• Monatomic anions typically end in -ide, while oxyanions (polyatomic that contain oxygen) use the suffixes -ate or -ite.

Organic Chemistry

• Organic chemistry studies compounds containing carbon, with hydrocarbons being the simplest class comprised solely of carbon and hydrogen.

Explore the foundational concepts of atomic structure and the significant experiments that shaped our understanding of atoms. Learn about subatomic particles, their characteristics, and the critical experiments conducted by Thomson, Millikan, Becquerel, and Rutherford that revealed the nature of atoms.