Ch. 4 - Atomic Structure Structure of the Atom History of the atom Chemical Symbols Subatomic Particles

Democritus (400 B.C.) Proposed that matter was composed of tiny indivisible particles Not based on experimental data Greek: atomos

Alchemy (next 2000 years) Mixture of science and mysticism. Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.

John Dalton (1807) British Schoolteacher Billiard Ball Model based his theory on others’ experimental data Billiard Ball Model atom is a uniform, solid sphere

John Dalton Dalton’s Four Postulates 1. Elements are composed of small indivisible particles called atoms. 2. Atoms of the same element are identical. Atoms of different elements are different. 3. Atoms of different elements combine together in simple proportions to create a compound. 4. In a chemical reaction, atoms are rearranged, but not changed.

Henri Becquerel (1896) Discovered radioactivity Three types: spontaneous emission of radiation from the nucleus Three types: alpha () - positive beta () - negative gamma () - neutral

J. J. Thomson (1903) Cathode Ray Tube Experiments Discovered Electrons beam of negative particles Discovered Electrons negative particles within the atom Plum-pudding Model

J. J. Thomson (1903) Plum-pudding Model positive sphere (pudding) with negative electrons (plums) dispersed throughout

Ernest Rutherford (1911) Gold Foil Experiment Discovered the nucleus dense, positive charge in the center of the atom Nuclear Model

Ernest Rutherford (1911) Nuclear Model dense, positive nucleus surrounded by negative electrons

Niels Bohr (1913) Bright-Line Spectrum Energy Levels Planetary Model tried to explain presence of specific colors in hydrogen’s spectrum Energy Levels electrons can only exist in specific energy states Planetary Model

Niels Bohr (1913) Bright-line spectrum Planetary Model electrons move in circular orbits within specific energy levels

Erwin Schrödinger (1926) Quantum mechanics Electron cloud model electrons can only exist in specified energy states Electron cloud model orbital: region around the nucleus where e- are likely to be found

Electron Cloud Model (orbital) Erwin Schrödinger (1926) Electron Cloud Model (orbital) dots represent probability of finding an e- not actual electrons

James Chadwick (1932) Discovered neutrons Joliot-Curie Experiments neutral particles in the nucleus of an atom Joliot-Curie Experiments based his theory on their experimental evidence

revision of Rutherford’s Nuclear Model James Chadwick (1932) Neutron Model revision of Rutherford’s Nuclear Model

Metal that forms bright blue solid compounds. A. Chemical Symbols Capitals matter! Element symbols contain ONE capital letter followed by lowercase letter(s) if necessary. Metal that forms bright blue solid compounds. Co vs. CO Poisonous gas.

B. Subatomic Particles in a neutral atom Most of the atom’s mass. NUCLEUS ELECTRONS in a neutral atom PROTONS NEUTRONS NEGATIVE CHARGE POSITIVE CHARGE NEUTRAL CHARGE Most of the atom’s mass. Atomic Number equals the # of...

B. Subatomic Particles 3 quarks = 1 proton or 1 neutron Quarks He 6 types He 3 quarks = 1 proton or 1 neutron

II. Electron Cloud Model Orbital Energy Levels Bohr Model Diagrams Ch. 4 - Atomic Structure II. Electron Cloud Model Orbital Energy Levels Bohr Model Diagrams

A. Orbital Can’t pinpoint the location of an electron. Region where there is 90% probability of finding an electron. Can’t pinpoint the location of an electron. Density of dots represents degree of probability.

A. Orbital Orbitals have different shapes.

B. Energy Levels Electrons can only exist at certain energy levels. Low energy levels are close to the nucleus. Each energy level (n) can hold 2n2 electrons.

C. Bohr Model Diagrams Simplified energy levels using Bohr’s idea of circular orbits. Can replace with: 3p 4n Lithium Atomic #: 3 Mass: 7 # of p: 3 # of e: 3 # of n: 4 e- e- p n Maximum e- Level 1 2e- Level 2 8e- Level 3 18e- Level 4 32e- e-

C. Bohr Model Activity Choose a number between 1 & 18. Find your element by the atomic number you picked. Draw a Bohr Model diagram for your element on your marker board. Round off the mass listed on the table and subtract the atomic # to find the # of neutrons. Abbreviate the # of ‘p’ and ‘n’ in the nucleus. Have a partner check your drawing. Repeat with a new element.

III. Masses of Atoms Atomic Mass Mass Number Isotopes Ch. 4 - Atomic Structure III. Masses of Atoms Atomic Mass Mass Number Isotopes

A. Atomic Mass 1 proton = 1 u 1 neutron = 1 u 1 u = 1.67  10-24 g atomic mass unit (u) 1 u = 1/12 the mass of a 12C atom 1 proton = 1 u 1 neutron = 1 u 1 u = 1.67  10-24 g © Addison-Wesley Publishing Company, Inc.

B. Mass Number Always a whole number. Sum of the protons and neutrons in the nucleus of an atom. © Addison-Wesley Publishing Company, Inc. Always a whole number. # of neutrons = mass # - atomic #

C. Isotopes Mass # Atomic # Isotope symbol: “Carbon-12” Atoms of the same element with different numbers of neutrons. Isotope symbol: Mass # Atomic # “Carbon-12”

C. Isotopes © Addison-Wesley Publishing Company, Inc.

C. Isotopes Average Atomic Mass reported on Periodic Table weighted average of all isotopes Avg. Atomic Mass

C. Isotopes EX: About 8 out of 10 chlorine atoms are chlorine-35. Two out of 10 are chlorine-37. Avg. Atomic Mass 35.4 u