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History Empedocles(440 B.C) Democritus (400 B.C.) Everything is composed of 4 elements and controlled by two forces Earth, Fire, Air, Water Love and Strife named the most basic particle atom- means “indivisible Aristotle (340 B.C.) didn’t believe in atoms thought matter was continuous Problem: No Evidence http://cwx.prenhall.com/petrucci/medialib/media_portfolio/02.html History by 1700s, all chemists agreed: on the existence of atoms that atoms combined to make compounds Still did not agree on whether elements combined in the same ratio when making a compound Law of Conservation of Mass Antonine Lavoisier (1782) mass is neither created or destroyed during regular chemical or physical changes Mass of Reactants = Mass of Products Law of Definite Proportions Joseph Proust (1799) any amount of a compound contains the same element in the same proportions by mass No matter where the copper carbonate is used, it still has the same composition Law of Multiple Proportions applies when 2 or more elements combine to make more than one type of compound the mass ratios of the second element simplify to small whole numbers Law of Multiple Proportions John Dalton 1803 Father of “Modern Atomic Theory” Started Teaching at age 12 Believed the atom was a solid sphere of one element Studied other scientists findings Dalton’s Atomic Theory 1. All matter is made up of atoms. Atoms are the smallest fundamental units of matter. Dalton’s Atomic Theory TRUE 1. All matter is made up of atoms. Atoms are the smallest fundamental units of matter. Dalton’s Atomic Theory TRUE 1. 2. All matter is made up of atoms. Atoms are the smallest fundamental units of matter. All elements consist of atoms which are indivisible & indestructible. Dalton’s Atomic Theory TRUE 1. FALSE 2. Nuclear reactions All matter is made up of atoms. Atoms are the smallest fundamental units of matter. All elements consist of atoms which are indivisible & indestructible. Dalton’s Atomic Theory TRUE 1. FALSE 2. Nuclear reactions All matter is made up of atoms. Atoms are the smallest fundamental units of matter. All elements consist of atoms which are indivisible & indestructible. 3. All atoms of the same element are identical in size, shape & mass. Dalton’s Atomic Theory TRUE 1. FALSE 2. Nuclear reactions FALSE Isotopes All matter is made up of atoms. Atoms are the smallest fundamental units of matter. All elements consist of atoms which are indivisible & indestructible. 3. All atoms of the same element are identical in size, shape & mass. Dalton’s Atomic Theory TRUE 1. FALSE Nuclear reactions 2. indivisible & indestructible. FALSE Isotopes TRUE All matter is made up of atoms. Atoms are the smallest fundamental units of matter. All elements consist of atoms which are 3. All atoms of the same element are identical in size, shape & mass. 4. Atoms of different elements are different in size, shape, & mass. Dalton’s Atomic Theory TRUE FALSE 1. 2. All matter is made up of atoms. Atoms are the smallest fundamental units of matter. All elements consist of atoms which are indivisible & indestructible. FALSE TRUE TRUE 3. All atoms of the same element are identical in size, shape & . mass 4. Atoms of different elements are different in size, shape, & mass. 5. In a chemical reaction, atoms are rearranged, never created nor destroyed & they combine in whole number ratios. Dalton’s Atomic Model Dalton’s Atomic Theory 1. 2. 3. 4. 5. All mass is made of atoms Atoms of same element have the same size, mass, and properties Atoms can’t be subdivided, created or destroyed Atoms of different elements combine in whole number ratios to make compounds In chemical reactions, atoms are combined, separated, and rearranged. Modern Atomic Theory Some parts of Dalton’s theory were wrong: atoms are divisible into smaller particles (subatomic particles) atoms of the same element can have different masses (isotopes) Most important parts of atomic theory: all matter is made of atoms atoms of different elements have different properties Atoms of different element combine in whole number ratios to make compounds Other contributions Faraday Helped to provide evidence of Dalton’s work Millikan His oil drop experiment determined the charge of an electron History JJ Thomson (1897) (Plum Pudding Model) Discovers the Electron Cathode Ray Tube Experiment (Goldstein in 1906) Positively Charged Particles JJ Thomson 4 Ideas of Electric Charge Atoms are generally neutral Electric charges are properties of particles of matter Exist in a single unit Electric charges cancel out Radioactivity Curie and Becquerel Becquerel used a uranium and found that it emitted radiation from it Marie Curie further investigated his work and classified the radiation into 3 forms Alpha Rays - Positively Charged Beta Rays - Negatively Charged Gamma Rays – No Charge History Ernest Rutherford (1910) Kiwi Gold Foil Experiment Discovery of Nucleus Rutherford discovered the nucleus by shooting alpha particles (have positive charge) at a very thin piece of gold foil he predicted that the particles would go right through the foil at some small angle The Results Most positive charges past through because the atom is mostly empty space. Some of the positive charges deflected because the atom contains some positive charge. Some of positive charges deflected straight back because there is a concentrated area of positive charge (nucleus). Discovery of Nucleus some particles (1/8000) bounced back from the foil this meant there must be a “powerful force” in the foil to hit particle back Predicted Results Actual Results Discovery of Nucleus Characteristics of “Powerful Force”: 1. dense- since it was strong enough to deflect particle 2. small- only 1/8000 hit the force dead on and bounced back 3. positively charged- since there was a repulsion between force and alpha particles How Powerful “It was if you shot 15 inch shell at a piece of tissue paper and it bounced back at you” • Ernest Rutherford Rutherford’s experiment explained that the neutral charge of most atoms… Rutherford’s Atomic Model _ _ _ +++ _ ++++ +++ _ Nucleus- Contains Protons _ Electrons surround nucleus Lots of empty space _ _ What about Mass … it didn’t account for the mass ratio of Helium to Hydrogen to be 4:1 If Rutherford was correct the mass of Helium to Hydrogen should be 2:1 James Chadwick 1891-1972 Proved the existence of Neutrons Electrically Neutral Particles having a mass slightly greater than that of protons …And Why? Why? Why? Don't the electrons get pulled to the center where the protons are? _ _ +++ _ _ ++++ _ _ +++ _ Neils Bohr 1913 Positively Charged Nucleus surrounded by electrons in orbit Primitive Model History of the Atom Structure of Atom Nucleus: contains protons and neutrons takes up very little space Electron Shell contains electrons takes up most of space Subatomic Particles includes all particles inside atom proton electron neutron charge on protons and electrons are equal but opposite to make an atom neutral, need equal numbers of protons and electrons Subatomic Particles number of protons identifies the atom as a certain element protons and neutrons are about same size electrons are much smaller nuclear force- when particles in the nucleus get very close, they have a strong attraction proton + proton proton + neutron neutron + neutron Properties of Subatomic Particles Atomic Particle Symbol Electric Charge Electron e- 1- Proton p+ 1+ Neutron n0 0 Approx. Mass (amu) Actual Mass 1/1840 9.11 x 10-28 1 1.67 x 10-24 1 1.67 x 10-24 Atoms Atom: smallest particle of an element that has all of the elements characteristics; composed of electrons, protons, & neutrons 17 Cl 35.45 17 = Atomic Number & # of Protons in an atom Cl = Atomic Symbol 35.453 = Atomic Mass (or Mass Number) = Protons+Neutrons ** A neutral atom always has the same # of protons & electrons ** Ion: an atom with a charge; due to the loss or gain of electrons Isotopes Isotope: When atoms of the same element have different mass numbers; due to different neutron #’s Ex: C12 & C14 - C12 has 6 neutrons and C14 has 8 neutrons The Atomic Mass of an element is the average mass of all known isotopes of that element Some isotopes are radioactive