To understand the function of “heuristic principles” let us consider J.J. Matthews (1994) emphasized the importance of heuristic principles in scientific inquiry and science education in similar terms. Monk and Osborne (1997) pointed out how many science curricula have forgotten Schwab's important epistemological distinction between the methodological (experimental data) and interpretative (heuristic principles) components. It tells us what meaning to assign these facts” (Schwab, 1974, p. In other words: “A fresh line of scientific research has its origins not in objective facts alone, but in a conception, a deliberate construction of the mind … this conception … tells us what facts to look for in the research. The densely-packed center of the atom is called the nucleus and represents 99.99% of an atom's mass.According to Schwab (1974) scientific inquiry tends to look for patterns of change and relationships which constitute the heuristic (explanatory) principles of our knowledge. ➞ reflected particles had a "direct hit" with the center. ➞ deflected particles are those that had come "close to" the positively-charged center.
➞ most alpha-particles pass directly through because the atom is mostly open space. Rutherford's experiments involved bombarding various atoms of gold foil with low-energy alpha particles (α-particles): = Rutherford's Gold Foil Experimentġ911 - Ernest Rutherford disproved Thomson's "Plum Pudding Model" of the atom and discovered the nucleus. ➞ The mass of an electron: m e = 9.1 x 10 -31 kg ➞ The charge of an electron: 1.6 x 10 -19 C = The Charge and Mass of the Electronġ909 - Robert Millikan performed experiments that determined the charge of an electron and the mass of an electron. NOTE - We are not mentioning the word "protons" here. ➞ tiny, negative, point-charges ( raisins) arranged in a spherical cloud ( pudding) of positive charge. In his Plum Pudding Model, Thomson assumes the electrons are spread out like raisins in a pudding: Thomson's Cathode Ray Tube Experiments inspired him to propose his "Plum Pudding Model" of the Atom. Because atoms were known to be neutral, Thomson reasoned that there must be a positive charge somewhere in the atom as well. Because the "cathode rays" were deflected away from the negative end of an applied electric field, Thomson postulated that the cathode rays are negatively-charged particles called electrons.Ģ.
When an outside electric field is applied (image on the right), we can see that the electrons (cathode rays) are attracted to the positive end of the applied electric field.ġ. These cathode rays are produced by the applied voltage between the two electrodes. Thomson's Cathode Ray TubeĪs you can see in the image below, cathode rays are streams of electrons running through the cathode ray tube from cathode to anode. Thomson as he conducted experiments with a cathode ray tube. The Electron = discovered in 1903 by J.J. 3 - Chemical Quantities and StoichiometryĤ - Types of Chemical Reactions and Solution Stoichiometryħ - Quantum Mechanical View of the Atom, and Periodicityĩ - Covalent Bonding and Molecular Orbitalsġ0 - Liquids, Solids, and Intermolecular Forcesġ5 - Applications of Acid-Base Equilibriaġ6 - Spontaneity, Entropy, and Free Energyġ8 - Transition Metals and Coordination ChemistryĢ0 - An Introduction to Organic Chemistryġ - Structural, Bonding, Molecular PropertiesĢ - The Nature of Organic Compounds: Alkanes and Cycloalkanesģ - Stereochemistry of Alkanes and Cycloalkanes: 3-D Structures of MoleculesĤ - The Study of Organic Reactions: An Overviewġ0 - Substitution (SN2, SN1) and Elimination (E2, E1) Reactionsġ1 - Mass Spectrometry and IR Spectroscopyġ3 - Conjugated Systems and UV Spectroscopyġ5 - Electrophilic Aromatic Substitution (E.A.S.)ġ8 - Aldehydes and Ketones: Nucleophilic Addition ReactionsĢ0 - Carboxylic Acid Derivatives and Nucleophilic Acyl Substitution ReactionsĢ1 - Carbonyl Alpha-Substitution Reactions