Presentation on theme: "From Philosophical Idea to Scientific Theory"— Presentation transcript:
1 From Philosophical Idea to Scientific Theory The AtomFrom Philosophical Idea to Scientific Theory
2 Dalton’s Model of the Atom Solid sphere:Solid indivisible sphere
3 Dalton’s Atomic Theory 1. All matter is composed of extremely small particles called atoms.2. Atoms of a given element are identical in size, mass, and other properties… different elements have different properties3. Atoms cannot be subdivided, created, or destroyed
4 Dalton’s Atomic Theory 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds5. In chemical reactions, atoms are combined, separated, or rearranged.
5 Modern Atomic Theory (what we believe about the atom today) Keeps some of Dalton’s postulates but others have been disproved. Now we know:1. Atoms are divisible even into smaller particles2. A given element can have atoms with different masses
6 Cathode-ray experiments Result of experiments between electricity and matterCarried out in cathode ray tubes: Many of these experiments involved passing electric current through gases at low pressures
8 CATHODE RAYS cont.Experiments to Investigate Relationship between Energy and MatterProcedure: Pass current from the cathode to the anode
9 1st Subatomic Particle Discovery RESULTS & HYPOTHESIS:Current passed through tube surface of the tube directly opposite the cathode glowedHypothesized glow caused by a stream of particles, which they called a cathode ray
10 EXPERIMENTS TO TEST INITIAL HYPOTHESIS MAIN RESULTS1. Object placed between cathode and opposite end of tube cast a shadow on the glass2. A paddle wheel placed on rails between the electrodes rolled along the rails from cathode toward anode.
11 RESULTS CONTINUED3. Cathode rays were deflected by a magnetic field in the same manner as a wire carrying electric current, which was known to have a negative charge4. The rays were deflected away from a negatively charged object.
12 HYPOTHESIS FROM THE OTHER EXPERIMENTS The particles that compose cathode rays are negatively charged
13 JJ ThomsonSupported Hypothesis (that cathode rays are negatively charged particles)Measured the ratio of the charge of cathode-ray particles to their mass: found it was always the same Therefore concluded that all cathode rays are composed of identical negatively charged particles (called electrons)
14 CHARGE & MASS OF ELECTRON Thomson’s ExperimentShowed that the electron has a very large charge for its tiny mass
17 ROBERT A. MILLIKAN’S EXPERIMENTS (1909) He showed that the mass of the electron is about one two-thousandth (1/2000) the mass of the simplest type of hydrogen atomMore accurate experiments show the mass is actually 1/1837 the mass of H
18 DISCOVERY OF THE ATOMIC NUCLEUS Rutherford’s Experiment (Draw Picture)
19 STARTLING RESULTSExpected the alpha particleds to pass through with only a slight deflection (assumed mass and charge were uniformly distributed throughout the atoms of the gold foil)Mostly true but about 1 in 8000 was redirected back toward source
20 RUTHERFORD’S CONCLUSIONS 1. Rebounded alpha particles must have experienced some powerful force within the atom2. The force must occupy a very small amount of space in the atom. The atom must be mostly empty space
21 RUTHERFORD’S CONCLUSIONS The force must be caused by a very densely packed bundle of matter with a positive electric charge.He called this bundle of matter the nucleus.
22 QUESTIONS LEFT TO PONDER WHERE WERE THE ELECTRONS?Rutherford suggested that the electrons surrounded the nucleus like planets around the sun but did not know what kept the electrons in motion around the nucleus
23 INSIDE THE ATOM – PART 2SUBATOMIC PARTICLES ISOTOPES AVERAGE ATOMIC WEIGHT
24 Subatomic particles Protons (p+) Neutrons (n0) Electrons (e-) Nucleus Determine the identity of the atomMoseley’s organization of periodic tableNeutrons (n0)Electrons (e-)Most important in determining element’s properties
25 Using Periodic Table Periodic Table – Element information Atomic # # protonsElementSymbolAverage AtomicWeight (amu)
26 Using Periodic Table Periodic Table – Element information Atomic # # protonsElementSymbolAverage AtomicWeight (amu)
27 Using Periodic Table Subatomic particle values: 1. Atomic # 2. Atomic Weight3. Mass #
32 Average atomic weight Example (Round to 2 decimal places) Silver exists as 51.84% 107Ag and 48.16% 109Ag. The actual mass of 107Ag is amu and the actual mass of 109Ag is amu. What is the average atomic mass?