4-1 Early Ideas of the Atom Democritus Greek Philosopher 460-370 B.C. Stated – Matter could be divided into smaller & smaller particles until it could no longer be divided. Called these Particles – Atomos (indivisible) Not based on any physical evidence, only thought.

Dalton’s Atomic Theory Late 1700’s – John Dalton – School Teacher(england) Dalton’s Atomic Theory – Summarized All matter is composed of extremely small particles called atoms. **Atoms of a given element are identical in size, mass, and other properties. (Isotopes - atoms same element with different mass.) **Atoms cannot be subdivide, created, or destroyed. Atoms of different elements can combine in simple, whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged.

3.2 Discovering Atomic Structure Particle arrangement of the atom. Protons (+) Electrons (-) Neutrons (0) Michael Faraday Made the connection between the atom and electricity.

J.J Thomson – Plum pudding Used a Cathode Ray Tube (CRT) Discovered electrons Charge and mass Electric current passed through low pressure gas in a glass tube.

Robert Millikan Millikan’s Oil-Drop Experiment Proved the mass and charge of all electrons are identical. By varying the charge on different drops, he noticed that the charge was always a multiple of -1.6 x 10 -19 C.

Ernest Rutherford Used the Gold Foil Experiment Marsden and Gieger performed the experiment Bombarded thin sheets of metal with (+) charged particles. Results of the Particle deflections Most traveled through Some Deflected in Both Directions Very Few Deflected Back

Rutherford vs. Thomson Plum Pudding Nuclear

Rutherford results Atoms Contained a Nucleus Central part of the atom. Very small and very massive = Very dense. All the mass of an atom. Positively charged, location of protons.

Protons and Neutrons E. Goldstein Sir James Chadwick Used canal rays in a cathode ray tube to prove the existence of protons. Positively charged particles that had significant mass moved towards the cathode. Sir James Chadwick Neutrons, were neutrally charged particles found in the nucleus to add mass to the atom and to act as “nuclear glue.”

Atoms are Empty Space Most all of matter’s mass comes from the nucleus and that consist of a tiny central part of the atom. The remain space between the atom and the electrons is empty.

Summary of the Atom Nucleus Electrons Protons Neutrons Positively charged particle found in the nucleus Gives mass to the atom. Neutrons Neutrally charged particle found in the nucleus. Gives mass to the atom and acts as “nuclear glue” Electrons Negatively charged particles that give the atom its size.

Properties of Subatomic Particles 4.2 How Atoms Differ Properties of Subatomic Particles Particle Symbols Relative Charge Mass Number Relative Mass Actual Mass Electron e- -1 0.00055 u 9.11 x 10-28g Proton p+ +1 1 1.00728 u 1.67 x 10-24g Neutron n0 1.00866 u 1.68 x 10-24g

Atomic Mass Units (amu) the equivalent mass of an atom. Protons = 1amu Neutrons = 1amu Electrons = 0 amu

Subatomic calculations Atomic Number (Z) –the number of protons within an atom. (Atomic # = p+) Every element has its own unique atomic number. p+ = e- , in an atom Mass # = p+ + n0

Isotope Abbreviations Atomic Symbol Notation: X = atomic symbol Mass Number form: name of element – mass#

Isotope Form Practice Write the element uranium with a mass # of 235 in atomic and mass form: Mass # = Atomic form =

Subatomic Particle Practice How many protons, neutrons and electrons do the following contain? Carbon – 13

Symbolic Form Mass Form Atomic # Mass # p+ n0 e-

Mass Form Symbol Form Atomic number Mass Number # Neutrons # Protons # Electrons   Calcium - 41 24 Na 11 12 13 9 8 5 2 206 82 Silver-109 186 W 74

Isotopes Atoms of the same element with different mass, due to the number of neutrons. The number of protons determines the identity of an atom !!!!!!! The number of neutrons can be different for the same type of element. Hydrogen

Hydrogen Isotope Names 3 isotopes of hydrogen Protium, Hydrogen – 1 Deuterium, Hydrogen – 2 Tritium, Hydrogen – 3

Relative Atomic Masses Although we know actual masses of atoms it is more practical to use their relative masses The arbitrary point – Carbon-12 1 atomic unit (a.u.) = Exactly 1/12 of C-12 All other atoms, weighed based upon Carbon-12

Atomic Mass Average mass of all naturally occurring isotopes of an element. Calculation Atomic mass = (mass of each isotope)(% abundance)/100 Add the answers to each of the isotopes to get the average mass.

Modern Atomic Theory Determine the atomic mass of Oxygen. Isotope Mass (amu) % abundance Oxygen – 16 15.994915 99.762 Oxygen – 17 16.999131 .038 Oxygen – 18 17.999160 .200

Modern Atomic Theory

Modern Atomic Theory Determine the atomic mass of Uranium. Isotope Mass (amu) % abundance Uranium-235 235.043924 .720 Uranium - 238 238.050784 99.280 Answer: Uranium =

4.4 Unstable Nuclei and Radioactive Decay Nuclear Reactions Changes that occur within an atom’s nucleus. Change the composition of the atom’s nucleus by altering the number of protons or neutrons. Strong Nuclear Forces Hold the nucleus together, neutrons help increase or add to this nuclear force.

4.4 Changes in the Nucleus Radioactive Decay Occurs when an atom emits one of the different forms of radiation. The original nucleus decomposes,”decays,” to form a new nucleus. The new nucleus will continue to decay until it reaches a stable configuration.

4.4 Types of Radioactive Decay Alpha Decay (Not a serious health hazard) Nucleus ejects a helium nucleus, called an alpha particle, and becomes a smaller nucleus with less positive charge. What would alpha decay of U-238 look like?

Alpha Decay

4.4 Beta Beta Decay (100 times more penetrating than alpha) The effect of turning a neutron in the nucleus into a proton, causing a beta particle (electron) to eject from the atom and the formation of a neutrino. Write the equation for the beta decay of sodium – 24.

Beta Decay

4.4 Gamma Gamma Decay High energy non-particle, with no charge or particle mass called a photon. Caused by the nucleus changing to a lower energy level, releasing photons in the form of x-ray or other high end radiation. Only stopped by thick concrete or lead. Extremely dangerous.

Gamma Decay