# Chapter reveiw.docx - 1 Atomic Theory Black Box An object...

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1 Atomic Theory Black Box An object with UNKNOWN internal structure. o Something who’s function is invisible o Function can be judged by observation Input BLACK BOX Output *Scientist used this theory to observer what inside an atom. Indirect observations and Inference is the act or process of deriving (drawing) logical conclusions from premises known or assumed to be true. (Unknown things that are assumed to be true.) The conclusion drawn is also called an idiomatic. Henri Bequerel (1852 – 1908) the discoverer of radioactivity along with Marie Skłodowska - Curie and Pierre Curie , for which all three won the 1903 Nobel Prize in Physics. 1. Alpha Particles a. A helium nucleus b. 2 p + , 2n 0 c. Symbol: 4 He 2. Beta Particle a. An electron that is emitted when a neutron splits into a proton and electron b. Symbol: -1 e 3. Gamma Ray a. High energy electromagnetic radiation b. A photon
2 Radioactivity Democritus (460-370 B.C.) An ancient Greek philosopher born in Abdera, Thrace, Greece. pre-Socratic philosopher who formulated an atomic theory for the universe. Billiard Ball (Democritus’s Theory) 1. Everything is composed of “atoms”, which are physically, but geometrically indivisible 2. Between atoms lies empty space 3. Atoms are indestructible 4. Atoms have been and always will be in motion 5. There are infinite number of atoms which differ in shape and size Note: His beliefs were lost for thousands of years in favour of Aristotle’s 4 element theory (Fire, Water, Air, Earth) John Dalton (1766-1844) Five main points of Dalton's atomic theory 1. Elements are made of extremely small particles called atoms . 2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. 3. Atoms cannot be subdivided, created, or destroyed. 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds . 5. In chemical reactions , atoms are combined, separated, or rearranged.
3 J.J. Thomson (1856-1940) Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, and thus is credited with the discovery and identification of the electron . *Thomson proposed that an electron is a negatively charged, extremely small part of an atom. J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons . Cathode ray experiment (Indirect observation) To test the properties of the particles, Thomson placed two oppositely- charged electric plates around the cathode ray. The cathode ray was deflected away from the negatively-charged electric plate and towards the positively-charged plate. This indicated that the cathode ray was composed of negatively-charged particles.
4 Plumb Pudding Model (Thomson’s Theory) Atoms are charged clouds of positive charge with negatively charged electrons embedded within Ernest Rutherford (1871-1937) Performed the Gold Foil Experiment Discoverer of the nucleus Gold Foil Experiment (Indirect observation) Rutherford aimed