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The Structure of the Atom Important contributors to the Atomic Theory Democritus Dalton Rutherford Aristotle J. J. Thomson Bohr The Atom: Early Theories Democritus versus Dalton similarities – Both believed Matter composed of extremely small particles called atoms All atoms of a given element are identical, but different from the atoms of other elements Atoms could not be created, divided, or destroyed Apparent changes in matter result from changes in the groupings of atoms The Atomic Theory: Democritus and Dalton differences – Democritus Matter is composed of empty space through which atoms move Different kinds of atoms come in different sizes and shapes The differing properties of atoms are due to the size, shape, and movement of atoms – Dalton Different atoms combine in simple whole number ratios to form compounds Dalton’s Atomic Theory The Atom: Subatomic particles and the nuclear atom How were the various parts of the atom discovered? – Electrons were discovered by the experiments of many scientists using cathode rays. JJ Thomson was able to determine the ratio of the electron’s charge to its mass Robert Millikan determined the charge of the electron and was able to calculate the mass of a single electron http://www.learnerstv.com/animation/animation.php?ani=18 6&cat=chemistry J. J. Thomson: Plum Pudding Model Discovery of subatomic particles – The nucleus was discovered by Ernest Rutherford and his gold foil experiment http://www.youtube.com/watch?v=5pZj0u_XMbc Rutherford refined his definition to include the proton Rutherford and James Chadwick discovered the neutron The atom Bohr- e- only have “allowable E states” e- around nucleus in orbits Particle Symbol Location electron e- Relative Relative Actual mass charge mass (g) electron cloud 1- 1/1840 9.11 x 10-28 proton p+ nucleus 1+ 1 1.673 x 10-24 neutron n0 nucleus 0 1 1.675 x 10-24 The Atom: How Atoms Differ Chemical name Atomic number Chemical Symbol Average Atomic Mass Atomic number = number of protons = number of electrons How many protons and electrons are in each of the following atoms? – boron – radon – platinum – magnesium An atom of an element contains 66 electrons. What element is it? An atom contains 14 protons. What element is it? Hydrogen 1 H 1.00794 LET’S REVIEW… 1. 2. 3. 4. 5. Which scientist came up with the plum pudding model? Why was it called this? Who discovered the nucleus of the atom? What was wrong with Dalton’s atomic theory? How many protons, neutrons, and electrons are in each of the following atoms? a) boron b) radon Let’s Review: Answers 1. 2. 3. 4. 5. Which scientist came up with the plum pudding model? J. J. Thomson Why was it called this? Who discovered the nucleus of the atom? Rutherford What was wrong with Dalton’s atomic theory? He stated that the atom was “indivisible” How many protons, neutrons, and electrons are in each of the following atoms? a) Boron: p+, e- = 5, no= 6 b) Radon: p+, e- = 86, no= 136 The Atom: How Atoms Differ cont Isotopes – An element with a different amount of neutrons in its nucleus – PROTON determines the ID – Representing isotopes: How atoms differ – Element – mass # – carbon – 12, carbon – 13, carbon – 14 – The mass number represents the total protons and neutrons in an element – How many protons, electrons, and neutrons in the following isotopes? Name each isotope and write its symbol. Atomic Structure: Isotopes Atomic masses of elements on the table are based on naturally occurring isotopes Weighted scale – abundance(mass) Average atomic mass = (mass 1 x rel. abundance 1) + (mass 2 x rel. abundance 2) Element C has two naturally occurring isotopes. The isotope with mass number 10 has a relative abundance of 20%. The isotope with mass number 11 has a relative abundance of 80%. Use these figures to estimate the average atomic mass for element C. State the atomic number and the true value of element C Atomic Structure: Isotopes – Complete the following table Isotope Atomic # Mass # 20 46 8 17 p+ e- n0 symbol 107 Ag 47 hydrogen-3 Types of Radiation – Alpha Radiation: radiation that is deflected toward the negatively charged plate. Each alpha particle contains two protons and two 226 222 4 neutrons. Ra Rn 88 86 2 He – Beta Radiation: radiation that was deflected toward the positively charged plate. Each beta particle is an electron. 14 6 C N 238 92 4 0 Ra234 Th He 2 90 2 0 14 7 o 1 – Gamma Radiation: high energy radiation that possesses no mass The Atom Review Atomic theories – Democritus vs. Dalton Subatomic particles and the atom – JJ Thompson – determined the charge to mass ratio of the electron – Robert Millikan – determined the charge and mass of the electron – Rutherford – discovered the nucleus and later the proton – Rutherford and James Chadwick – discovered the neutron Atomic Number Isotopes Average Atomic Mass Types of Radiation