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2 S.MORRIS 2006 More free powerpoints at

3 The Hellenic Market FireWater Earth Air ~ ~

4 The Greeks History of the Atom Not the history of atom, but the idea of the atom In 400 B.C the Greeks tried to understand matter (chemicals) and broke them down into earth, wind, fire, and air. Democritus and Leucippus Greek philosophers  

5 460 BC Democritus develops the idea of atoms he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible) No experiments to support idea Continuous vs. discontinuous theory of matter Democritus’s model of atom No protons, electrons, or neutrons Solid and INDESTRUCTABLE

6 Four Element Theory Plato was an atomist Thought all matter was composed of 4 elements: –Earth (cool, heavy) –Water (wet) –Fire (hot) –Air (light) –Ether (close to heaven) ‘MATTER’ FIRE EARTHAIR WATER Hot Wet Cold Dry Relation of the four elements and the four qualities Blend these “elements” in different proportions to get all substances

7 Anaxagoras Anaxagoras (Greek, born 500 B.C.) seeds –Suggested every substance had its own kind of “seeds” that clustered together to make the substance, much as our atoms cluster to make molecules. Some Early Ideas on Matter O’Connor Davis, MacNab, McClellan, CHEMISTRY Experiments and Principles  1982, page 26, Empedocles Empedocles (Greek, born in Sicily, 490 B.C.) – earth, air, fire, and water –Suggested there were only four basic seeds – earth, air, fire, and water. The elementary substances (atoms to us) combined in various ways to make everything. Democritus (Thracian, born 470 B.C.) proposed the word atom –Actually proposed the word atom (indivisible) because he believed that all matter consisted of such tiny units with voids between, an idea quite similar to our own beliefs. It was rejected by Aristotle and thus lost for 2000 years. Aristotle Aristotle (Greek, born 384 B.C.) – heat, cold, dryness, moisture – as basic elements –Added the idea of “qualities” – heat, cold, dryness, moisture – as basic elements which combined as shown in the diagram (previous page). Hot + dry made fire; hot + wet made air, and so on. Some Ancient Thoughts About Matter: Democritus and Aristotle. (02:03)Some Ancient Thoughts About Matter: Democritus and Aristotle. Video Segment 1 of 6 from the Full Video

8 Who Was Right? Greek society was slave based Beneath famous to work with hands did not experiment Greeks settled disagreements by argument Aristotle was more famous He won! His ideas carried through middle ages. Alchemists change lead to gold California WEB

9 Alchemy After that chemistry was ruled by alchemy. They believed that that could take any cheap metals and turn them into gold. Alchemists were almost like magicians. –elixirs, physical immortality

10 Contributions of alchemists: Information about elements - the elements mercury, sulfur, and antimony were discovered - properties of some elements Develop lab apparatus / procedures / experimental techniques - alchemists learned how to prepare acids. - developed several alloys - new glassware

11 HISTORY OF THE ATOM 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

12 “POP QUIZ”! Define the following terms on a separate sheet of paper –Atomic number –Ion –Molecule –Atom –Kernel Electrons

13 How’d You Do? The number of protons in the nucleus of an atom of an element An atom or group of atoms that has a positive or negative charge due to a gain or loss of electrons A neutral chemically bonded group of atoms that act as a unit The smallest particle of an element that retains the properties of that element An electron that is not considered to be part of the valence shell

14 HISTORY OF THE ATOM 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

15 HISTORY OF THE ATOM Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge 1904 like plums surrounded by pudding. PLUM PUDDING MODEL

16 HISTORY OF THE ATOM 1910 Ernest Rutherford oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit Ernest Rutherford's Experiment.Ernest Rutherford's Experiment. (00:59) Video Segment 2 of 6 from the Full Video Matter and Energy: Matter: What Is It? 09/20/07 6 - 8 The Structure and Scale of the Atom. (02:46) Matter and Energy: Matter: What Is It? The Structure and Scale of the Atom. Video Segment 3 of 6 from the Full Video

17 HISTORY OF THE ATOM gold foil helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back. helium nuclei

18 HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.

19 HISTORY OF THE ATOM 1913 Niels Bohr studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

20 Bohr’s Atom electrons in orbits nucleus

21 HELIUM ATOM + N N + - - proton electron neutron Shell What do these particles consist of?

22 Timeline 20001000300 AD American Independence (1776) Issac Newton (1642 - 1727) 400 BC Greeks (Democratus ~450 BC) Discontinuous theory of matter ALCHEMY Greeks (Aristotle ~350 BC)) Continuous theory of matter

23 ATOMIC STRUCTURE Particle proton neutron electron Charge + ve charge -ve charge No charge 1 1 nil Mass

24 ATOMIC STRUCTURE the number of protons in an atom the number of protons and neutrons in an atom He 2 4 Atomic mass Atomic number number of electrons = number of protons

25 Complete the following table in your notes Atomic #Mass ## of Protons # of Neutrons # of Electrons 910 1415 4722 5525

26 Isotopes Atoms that have the same number of protons but different numbers of neutrons Different mass numbers Chemically alike because they have identical numbers for the characteristic chemical behavior of each element Ex: Three known isotopes for H –Hydrogen (no neutrons, mass # of 1) –Deuterium (one neutron, mass # of 2) –Tritium (two neutrons, mass # of 3)

27 Your turn… Two of the isotopes for Carbon are Carbon-12 and Carbon-13, write the chemical symbol for both – 12 6 C – 13 6 C Three isotopes for Oxygen are oxygen-16, oxygen-17, and oxygen-18, write the chemical symbol for all three – 16 8 O – 17 8 O – 18 8 O

28 Calculating Average Atomic Mass of Isotopes In nature, isotopes occur in various percentages In order to figure out the average mass of each element the percent abundance and mass of each isotope need to be considered We can calculate average atomic mass in much the same way as we calculate your grade in this class…

29 What are the different categories that you are graded on in this class? Classwork: 79% Practice: 7% Final: 14% What would your semester grade be if you received an 80% for classwork, 50% for practice, and 72% on your final? –0.80 x 79 = 63.2 –0.50 x 7 = 3.5 –0.72 x 14 = 10.1 –Add all answers together to get % semester grade: 63.2 + 3.5 + 10.1 = 76.8 % (a C)

30 Now lets try with an element! Copper has two isotopes: copper-63 and copper-65. The relative abundances of these isotopes are 69.2% and 30.8% respectively. Calculate the average atomic mass of copper. 0.692 x 63 = 43.60 0.308 x 65 = 20.02 43.6 + 20.02 = 63.62

31 One more example… Uranium has three naturally occurring isotopes with the following percent abundances: U-234 (0.0058%), U-235 (0.71%), and U-238 (99.23%). –What do you expect the average atomic mass to be and why? –What is the average atomic mass? 237.85

32 ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shella maximum of 2 electrons second shella maximum of 8 electrons third shella maximum of 8 electrons

33 SUMMARY 1. The Atomic Number of an atom = number of protons in the nucleus. 2. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. 3. The number of Protons = Number of Electrons. 4. Electrons orbit the nucleus in shells. 5. Each shell can only carry a set number of electrons.

34 ATOMIC STRUCTURE There are two ways to represent the atomic structure of an element or compound; 1.Electronic Configuration 2.Dot & Cross Diagrams

35 ELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; N Nitrogen 7 14 2 in 1 st shell 5 in 2 nd shell configuration = 2, 5 2 + 5 = 7

36 ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; Ca O ClSi Na 20 40 11 23 8 17 16 35 14 28 B 11 5 a)b)c) d)e)f) 2,8,8,22,8,1 2,8,72,8,42,3 2,6

37 DOT & CROSS DIAGRAMS With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; Nitrogen N XX X X XX X N 7 14

38 DOT & CROSS DIAGRAMS Draw the Dot & Cross diagrams for the following elements; OCl 817 16 35 a)b) O X X X X X X X X Cl X X X XX X X X X X X X X X X X X

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