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 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=186&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 Relative charge Relative mass Actual mass (g) electron e- electron cloud 1- 1/1840 9.11 x 10-28 proton p+ nucleus 1+ 1 1.673 x 10-24 neutron n0 1.675 x 10-24

The Atom: How Atoms Differ Hydrogen 1 H 1.00794 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?

LET’S REVIEW… 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? boron radon

Let’s Review: Answers 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? Boron: p+, e- = 5, no= 6 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 # p+ e- n0 symbol 20 46 8 17 Ag hydrogen-3 107 47

Types of Radiation Alpha Radiation: radiation that is deflected toward the negatively charged plate. Each alpha particle contains two protons and two neutrons. Beta Radiation: radiation that was deflected toward the positively charged plate. Each beta particle is an electron. 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