3 The Greeks History of the Atom In 400 B.C the Greeks tried to understand matter (chemicals) and broke them down into earth, wind, fire, and air.~
4 Greek Model Democritus Greek philosopher Idea of ‘democracy’ “To understand the very large, we must understand the very small.”DemocritusGreek philosopherIdea of ‘democracy’Idea of ‘atomos’Atomos = ‘indivisible’‘Atom’ is derivedNo experiments to support ideaContinuous vs. discontinuous theory of matterAtomists; they argued for a completely materialistic universe consisting of atoms moving in a void.Since mere fragments of the ideas of Leucippus are known, his pupil, Democritus of Abdera (c B.C.)is considered the elaborator of this concept.Aaron J. Ihde The Development of Modern Chemistry, Dover Publishing, 1984 pg 6It should also be noted that the Romans were not a scientific people and made almost no scientific contributions of their own.“To understand the very large, we must understand the very small.”-DemocritusThe worldReality to Democritus consists of the atoms and the void. Atoms are indivisible, indestructible, eternal, and are in constant motion. However, they are not all the same as they differ in shape, arrangement and position. As the atoms move they come into contact with other atoms and form bodies. A thing comes into being when the atoms that make it up are appropriately associated and passes away when these parts disperse.This leaves no room for the intelligent direction of things, either by human or divine intelligence, as all that exists are atoms and the void. Democritus stated, "Nothing occurs at random, but everything occurs for a reason and by necessity."The soulAlthough intelligence is not allowed to explain the organization of the world, according to Democritus, he does give place for the existence of a soul, which he contends is composed of exceedingly fine and spherical atoms. He holds that, "spherical atoms move because it is their nature never to be still, and that as they move they draw the whole body along with them, and set it in motion." In this way, he viewed soul-atoms as being similar to fire-atoms: small, spherical, capable of penetrating solid bodies and good examples of spontaneous motion.Democritus’s model of atomNo protons, electrons, or neutronsSolid and INDESTRUCTABLE
5 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’FIREEARTHAIRWATERHotWetColdDryTHE SCEPTICAL CHYMIST (1661)“The Greeks believed that earth, air, fire, and water were the fundamental elements that made up everything else. Writing in 1661, Robert Boyle ( ) argued against this idea, paving the way for modern ideas of the elements. He defined an element accurately as a substance that could not be broken down into simpler substances.”Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 18Plato was Aristotle's student. It was Aristotle that suggested qualities of "hot, dry, cold, wet".Relation of the four elements and the four qualitiesBlend these “elements” in different proportions to get all substances
6 Some Early Ideas on Matter Anaxagoras (Greek, born 500 B.C.)Suggested every substance had its own kind of “seeds” that clustered together to make the substance, much as our atoms cluster to make molecules.Empedocles (Greek, born in Sicily, 490 B.C.)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.)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 (Greek, born 384 B.C.)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.O’Connor Davis, MacNab, McClellan, CHEMISTRY Experiments and Principles 1982, page 26,
7 Who Was Right? did not experiment Aristotle was more famous He won! His ideas carried through middle ages.California WEB
8 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
9 AlchemyAlchemical symbols for substances…. . .. ..GOLDSILVERCOPPERIRONSANDtransmutation: changing one substance into anotherDIn ordinary chemistry, we cannot transmute elements.
11 Contributions of alchemists: Information about elements - the elements mercury, sulfur, and antimony were discovered- properties of some elementsDevelop lab apparatus / procedures / experimental techniques- alchemists learned how to prepare acids.- developed several alloys- new glassware
14 Dalton’s Symbols John Dalton 1808 Jons Jakob Berzelius ( ) Swedish chemist who invented modern chemical symbols.Berzelius discovered the elements silicon, selenium, cerium, and thorium.John Dalton1808
15 Subatomic particles Electrons: Negatively charged subatomic particles Discovered by J.J. ThomsonDiscovered by observing deflection of cathode rays.National High Magnetic Field Laboratory: Electromagnetic Deflection in a Cathode Ray Tube (I) Tutorial
16 Protons : positively charge particles Neutrons: no charge particles, mass similar to protons.The atomic nucleus:Protons and neutrons are located in the center of the atomThrough the gold-foil experiment, Rutherford determined: YouTube - Rutherford's Experiment: Nuclear AtomThe atom is mostly empty spacePositive charge and most of atom’s mass is concentrated in a small region, called the nucleus (composed of protons and neutrons)
17 Distinguishing Among Atoms Elements are different because they contain different number of protons.Atomic number: indicates the number of protons in the nucleus of an element.Since atoms are electronically neutral:# protons= # electronsAtomic number:Carbon has 6 protonsCarbon has 6 electrons6C
18 Electron MicroscopyImages of objects are produced by using an electron beam.Typical light microscope magnifies up to 1000 xElectron microscope magnifies over 100,000 xSEM - Image Gallery
19 Learning Check: complete the following table ElementSymbolAtomic number# protons# electrons1.Tin2.163.814.765.Gd
20 Learning Check: complete the following table ElementSymbolAtomic number# protons# electrons1.TinSn502.SulfurS163.ThalliumTl814.OsmiumOs765.GadoliniumGd64
21 Au Mass number gold-197 Mass number 197 79 Most of the mass of an atom is concentrated in its nucleus and depends on the number of protons and neutrons.Mass number: total number of protons and neutrons in an atom.# neutrons= mass number – atomic numberRepresenting atoms:Mass numberMass numberAu19779gold-197Atomic number
22 Learning check: determine the number of protons, neutrons and electrons for the following atoms. Carbon-12Fluorine-19Beryllium-9
23 Learning check: determine the number of protons, neutrons and electrons for the following atoms. Carbon-12 p+= 6 e-=6 no= 6Fluorine-19 p+= 9 e-=9 no= 10Beryllium-9 p+= 4 e-=4 no= 5
26 IsotopesIsotopes are atoms of the same element that have the same number of protons, but different number of neutrons.Isotopes of an element have the same atomic number but different number of neutrons, thus have different mass numbers.Hydrogen has 3 isotopes:Hydrogen-1 or simply hydrogenHydrogen-2 or deuteriumHydrogen-3 or tritium
27 Learning check: write the symbol (including atomic number and mass number )for the following isotopes.oxygen-17, oxygen-18Chromium-50, chromium-52, chromium-53
28 Learning check: write the symbol (including atomic number and mass number )for the following isotopes.oxygen-17, oxygen-18O OChromium-50, chromium-52, chromium-53Cr Cr Cr171888505253242424
29 Atomic Mass Mass of proton or neutron: 1.67x10-24g Mass of electron : x10-28gThese values are impractical to work with, so scientists compare relative masses of atoms using a reference isotope : carbon-12An atomic mass unit (amu) is defined as 1/12 the mass of carbon-12
30 Atomic mass (continued) The atomic mass of an element is not a whole number because the isotopes of an element and its natural abundance is taken in consideration.The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.
31 Atomic mass (continued) Ex. 1 The atomic mass of copper is amu. Which of copper’s two isotopes is more abundant: copper-63 or copper-65?Since is closer to 63 than 65, the most abundant isotope is copper-63.
32 Atomic mass (continued) Ex. 3 There are 3 isotopes of silicon; they have mass numbers of 28, 29, and 30. The atomic mass of silicon is amu. Comment on the relative abundance of these 3 isotopes.Silicon-28 must be the most abundant.
33 Atomic mass (continued) Ex. 2 Calculate the atomic mass of bromine. The two isotopes of bromine have atomic masses and relative abundance of amu (50.69%) and amu (49.31%)1. Divide the percentages by 100: andatomic mass= (0.5069x78.92) + (0.4931x80.92)== amu (remember units and sig figs)
34 Atomic mass (continued) Classwork p103 # 12,13; p 105 #33-34