The document describes the major historical atomic theories: 1) The Greek model proposed by Democritus that all matter is made of indivisible atoms of different shapes and sizes. Aristotle disagreed and proposed matter is made of four elements. 2) Dalton's atomic theory (1803) proposed that elements are made of atoms, atoms of the same element have the same mass, and compounds contain atoms of different elements combined in fixed ratios. 3) Thomson's model (1897) proposed atoms are made of even smaller particles in a "plum pudding" model, with positive charge throughout and negative electrons scattered within. 4) Rutherford's model (1911) from his gold foil experiment showed atoms have a

1. Warm-Up What is the symbol for the following elements. Gold Au Aluminum Al Sodium Na Lithium Li

2. 3-1 – Atomic Theories Objectives Describe the four main models of the atom and explain how each was discovered.

4. Greek Model of Atoms 400 B.C. Greek philosopher Democritus “ atomos” which means, indivisible. Atoms are hard, solid particles same material different shapes and sizes.

5. Greek Model (cont.) Aristotle disagreed with Democritus. Aristotle said there was no limit to division of matter. Aristotle thought matter consisted of four types. Fire, Earth, Water, Air

6. Dalton’s Atomic Theory 1803 – John Dalton, English Chemist All elements are composed of atoms. All atoms of the same element = mass Compounds contains atoms of more than one element. In a compound, atoms of different elements always combine in the same way H 2 O Na 2 CO 3

8. Thomson’s Model 1897 – J.J. Thomson, English Chemist. Atoms are made of even smaller particles. Plum pudding model Positively charged “pudding” through which negative particles are scattered. Atoms are neutral, therefore, there must be + particles too, but Thomson never found them .

9. Thompson’s Experiment

10. Rutherford’s Atomic Model 1911 – Ernest Rutherford, British physicist Gold Foil experiment. Atom has a small, dense positively charged center called the Nucleus. Negative electrons are scattered outside the nucleus. If an atom was the size of a baseball stadium, the nucleus would be the size of a marble.

12. Rutherford’s Experiment A beam of + particles (alpha particles) shot through a thin sheet of gold foil. Most particles passed straight through. (Most of atom is empty space.) A few were deflected. (Positive core-similar charges repel each other.) Very few bounced off. (Solid core is very small.)

13. Actual Results. Results of foil experiment if Plum Pudding model had been correct.

15. Three Way to Remember the Models D ogs S ort S ocks = D alton’s S olid S phere T urtles P lay P ing-pong = T homson’s P lum P udding R ats P lay N intendo = R utherford’s P ositive N ucleus

16. 3-1 Summary Who founded atomic theory? Ancient Greeks founded atomic theory. Thought matter was made up of four elements Democritus believed all matter was made up of atoms. Who founded modern atomic theory? John Dalton, father of modern atomic theory. Developed atom theory; Solid sphere Element have same make up Compounds always combine the same way.

17. 3-1 Summary (Cont.) Thomson Atomic Theory Experiment with Cathode ray tubes. Atoms are made up of smaller particles. Plum Pudding model Rutherford Atomic Theory Gold foil experiment Discovered the nucleus Positive nucleus

18. Warm Up Oops!! Those “harmless” Germanium capsules you just swallowed may have an extra proton in each nucleus. Is this good news or bad news? Why? This is bad news, for germanium nucleus with an additional proton is not Germanium, but arsenic!!!!