Chapter 4 Atomic Structure

A Long, Long Time Ago… Greek Philosophers- 4 elements are Earth, Water, Fire, and Air Greek Philosophers- 4 elements are Earth, Water, Fire, and Air Aristotle- first recorded atomic thoughts Aristotle- first recorded atomic thoughts Matter is continuous (no atoms) Matter is continuous (no atoms) Democritus (400 B.C.) - first recorded atomic theory Democritus (400 B.C.) - first recorded atomic theory Atoms are smallest part of matter, each type of matter has different atoms Atoms are smallest part of matter, each type of matter has different atoms

Aristotle and Democritus

A Long Time Ago… Antoine Lavoisier (1782) Antoine Lavoisier (1782) –Used experiments in closed containers to develop the LCM Joseph Proust (1799) Joseph Proust (1799) –Analyzed water to develop the Law of Definite Proportions John Dalton (1803) John Dalton (1803) –Compiled past research to develop the first useful atomic theory

Lavoisier and Proust

John Dalton Dalton’s theory had 4 major tenets Dalton’s theory had 4 major tenets 1.All matter is composed of atoms 2.Atoms are indivisible 3.Atoms of 1 element are alike, but different from those of other elements 4.Atoms combine in small, whole number ratios to form compounds

A Reminder Observation, Observation, Observation Observation, Observation, Observation Research Research Hypothesis Hypothesis Experiment, Revise hypothesis lots of times Experiment, Revise hypothesis lots of times Results match….may become a theory Results match….may become a theory

A Little While Ago… J.J. Thomson discovers the electron using a cathode ray tube J.J. Thomson discovers the electron using a cathode ray tube

Cathode Ray Tube Experiment htm htm htm

The Nucleus Exists! Ernest Rutherford uses the gold foil experiment to “discover” the nucleus Ernest Rutherford uses the gold foil experiment to “discover” the nucleus

The Gold Foil Experiment

Results of Gold Foil Experiment… nnotes/atomic/atomicmodelsandspectra.asp nnotes/atomic/atomicmodelsandspectra.asp nnotes/atomic/atomicmodelsandspectra.asp nnotes/atomic/atomicmodelsandspectra.asp rford/ rford/ rford/ rford/ Over 98% of the particles went straight through Over 98% of the particles went straight through About 2% of the particles went through but were deflected by large angles About 2% of the particles went through but were deflected by large angles About 0.01% of the particles bounced off the gold foil About 0.01% of the particles bounced off the gold foil

Rutherford’s Conclusion

Rutherford's Nuclear Model 1. The atom contains a tiny dense center called the nucleus 1. The atom contains a tiny dense center called the nucleus –the volume is about 1/10 trillionth the volume of the atom 2. The nucleus is essentially the entire mass of the atom 2. The nucleus is essentially the entire mass of the atom 3. The nucleus is positively charged 3. The nucleus is positively charged –the amount of positive charge of the nucleus balances the negative charge of the electrons 4. The electrons move around in the empty space of the atom surrounding the nucleus 4. The electrons move around in the empty space of the atom surrounding the nucleus

Understanding Periodic Blocks K Atomic Number Atomic Number –# of protons Element Symbol Element Symbol Mass Number Mass Number –Protons + Neutrons

Can Neutrons Exist??? No, is an average mass of all natural K atoms No, is an average mass of all natural K atoms –All K atoms MUST have 19 protons –Some have 20 neutrons, some 19, some 21… –Average is neutrons –Individual isotopes are identified by the number of neutrons

Identifying Protons, Neutrons, and Electrons Chlorine-35 (element-mass number) Chlorine-35 (element-mass number) # of protons = 17 # of protons = 17 # electrons = # protons # electrons = # protons # neutrons = mass number – protons # neutrons = mass number – protons –35-17 = 18 Why no electrons in atomic mass? Why no electrons in atomic mass? –Electron has mass 1/1837 of Proton and Neutron

Nuclear Stability

The Modern View of the Atom Neils Bohr (1913) develops the planetary model of the atom Neils Bohr (1913) develops the planetary model of the atom –Developed from “electrocution” of hydrogen gas –Only certain colors resulted –Why??? ntumzone/index.html ntumzone/index.html ntumzone/index.html ntumzone/index.html

Bohr’s Hydrogen Atom odule_viewer.php?mid=51 odule_viewer.php?mid=51

Schrodinger’s Revision…