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Chemistry What is Chemistry? The study of matter and the changes which it undergoes • Metallurgy – Bronze Age, Iron Age PRIMITIVE MAN DISCOVERS • MELTING POINTS • GLASS MAKING • GLAZES Egypt and Mesopotamia - Discover chemical processes and methods - Metal workers hand down their methods to their children, but don’t write much down on paper (scrolls) - Pass on knowledge to the Greeks • Plato (400 BC) - four elements: earth, water, fire and air Fire Earth Air Water History of the atom • Not the history of atom, but the idea of the atom • Original idea Ancient Greece (400 B.C..) • Democritus and Leucippus Greek philosophers • Called minute particles “Seeds” History of Atom • Looked at beach Smallest possible piece? • Made of sand • Cut sand - smaller Atomos - not to be cut sand Another Greek • • • • • • • Aristotle - Famous philosopher All substances are made of 4 elements Fire - Hot Air - light Earth - cool, heavy Water - wet Blend these in different proportions to get all substances Hellenistic Culture • Not much experimentation, just speculation • ideas carried through middle ages. • Alchemists change lead to gold • Alchemy – Middle Ages The Alchemist’s Dream COPPER “SILVER” Zinc coated “GOLD” Brass = Copper + Zinc Penny into Gold - Alchemist Dream Timeline Greeks (Democratus ~450 BC) Discontinuous theory of matter ALCHEMY 400 BC 300 AD Issac Newton (1642 - 1727) 1000 2000 Greeks (Aristotle ~350 BC)) Continuous theory of matter American Independence (1776) Alchemy In Europe, alchemy was the quest for the Philosopher’s Stone. Allegedly, this substance would turn cheap metals into gold. Transmutation changing one substance into another COPPER Philosopher’s Stone GOLD 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 Modern Chemistry evolved from Alchemy • Antionne Lavoisier (1785) - Chemistry as a science began with Lavoisier - Relied on quantitative, reproducible experiments - Prepared a textbook of Chemistry Who’s Next? • Late 1700’s - John Dalton- England • Teacher- summarized results of his experiments and those of other’s • In Dalton’s Atomic Theory • Combined ideas of elements with that of atoms • John Dalton (1808) – Atomic Theory All matter consists of atoms are tiny indivisible particles of an element that cannot be created or destroyed. Atoms of one element cannot be converted into atoms of another element. Atoms of an element are identical and are different from atoms of any other element. Dalton’s Atomic Theory All matter is made of tiny indivisible particles called atoms. Atoms of the same element are identical, those of different atoms are different. Atoms of different elements combine in whole number ratios to form compounds Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed. Dmitri Mendeleev (1834-1907) In 1869, Mendeleev, a Russian chemist, made a list of all the chemical elements that were known at that time, sorted according to increasing atomic mass. There were many gaps in the table, and according to them, Mendeleev was able to forecast that new elements would be found to fill the gaps. Modern Periodic Table Parts of Atoms • J. J. Thomson - English physicist. 1897 • Made a piece of equipment called a cathode ray tube or CRT. • It is a vacuum tube - all the air has been pumped out. J. J. Thomson and his CRT Thomson’s Experiment Voltage source - + Vacuum tube Metal Disks Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source • By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field he found that the moving pieces were negative Thomson’s Model • Found the electron • Couldn’t find positive (for a while) • Said the atom was like plum pudding • A bunch of positive stuff, with the electrons able to be removed Rutherford’s experiment • Ernest Rutherford English physicist. (1910) • Believed in the plum pudding model of the atom. • Wanted to see how big they are • Used radioactivity • Alpha particles - positively charged pieces given off by uranium • Shot them at gold foil which can be made a few atoms thick Rutherford’s experiment • When the alpha particles hit a florescent screen, it glows. • Here’s what it looked like (pg 72) Lead block Uranium Florescent Screen Gold Foil He Expected • The alpha particles to pass through without changing direction very much • Because • The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles What he expected Because Because, he thought the mass was evenly distributed in the atom Because, he thought the mass was evenly distributed in the atom What he got How he explained it • Atom is mostly empty • Small dense, positive piece at center • Alpha particles are deflected by it if they get close enough + Movie + Density and the Atom • Since most of the particles went through, it was mostly empty. • Because the pieces turned so much, the positive pieces were heavy. • Small volume, big mass, big density • This small dense positive area is the nucleus Modern View of the Atom • The atom is mostly empty space • Two regions • Nucleus- protons and neutrons • Electron cloudregion where you might find an electron Structure of the Atom • • • • • • There are two regions The nucleus With protons and neutrons Positive charge Almost all the mass Electron cloud- Most of the volume of an atom • The region where the electron can be found Size of an Atom • • • • • Atoms are small. Measured in picometers, 10-12 meters Hydrogen atom, 32 pm radius Nucleus tiny compared to atom If the atom was the size of a stadium, the nucleus would be the size of a marble. • Radius of the nucleus near 10-15m. • Density near 1014 g/cc Subatomic Particles Relative Actual mass (g) Name Symbol Charge mass Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron n0 0 1 1.67 x 10-24 Counting the Pieces • Atomic Number = number of protons • # of protons determines kind of atom • The same as the number of electrons in the neutral atom • Mass Number = the number of protons + neutrons • All the things with mass Symbols • Contain the symbol of the element, the mass number and the atomic number Symbols • Contain the symbol of the element, the mass number and the atomic number Mass number Atomic number X Symbols • Find the – number of protons – number of neutrons – number of electrons – Atomic number – Mass Number 19 9 F Symbols Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass Number 80 35 Br Symbols If an element has an atomic number of 34 and a mass number of 78 what is the –number of protons –number of neutrons –number of electrons –Complete symbol Symbols If an element has 91 protons and 140 neutrons what is the –Atomic number –Mass number –number of electrons –Complete symbol Symbols If an element has 78 electrons and 117 neutrons what is the –Atomic number –Mass number –number of protons –Complete symbol Isotopes • Dalton was wrong. • Atoms of the same element can have different numbers of neutrons • Different mass numbers • Called isotopes Naming Isotopes • Put the mass number after the name of the element • carbon- 12 • carbon -14 • uranium-235 Atomic Mass • • • • How heavy is an atom of oxygen? There are different kinds of oxygen atoms. More concerned with average atomic mass. Based on abundance of each element in nature. • Don’t use grams because the numbers would be too small Measuring Atomic Mass • Unit is the Atomic Mass Unit (amu) • One twelfth the mass of a carbon-12 atom. • Each isotope has its own atomic mass we need the average from percent abundance. Calculating averages • You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks? • Total mass = 4 x 50 + 1 x 60 = 260 g • Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 • Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 5 Calculating averages • Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 5 • Average mass = .8 x 50 + .2 x 60 • 80% of the rocks were 50 grams • 20% of the rocks were 60 grams • Average = % as decimal x mass + % as decimal x mass + % as decimal x mass + Atomic Mass • Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu. Atomic Mass • Magnesium has three isotopes. 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 25 with a mass of 25.9826 amu. What is the atomic mass of magnesium? • If not told otherwise, the mass of the isotope is the mass number in amu Atomic Mass • Is not a whole number because it is an average. • Are the decimal numbers on the periodic table. The Periodic Table States • Different states of a substance are different physical ways of packing its component particles. Some elements and all compounds consist of molecules or crystal lattices, which in turn consist of atoms or ions joined by chemical bonds. 2 or more elements combined in a unique ratio •Are basic forms of MATTER IRON CALCIUM SULFUR SODIUM •Cannot be broken down into simpler substances by chemical reactions Lustre conduct electricity ductile malleable high melting points and densities Na sodium Solids at room temperature except mercury Hg K potassium Mg magnesium Cu copper Ag Silver Fe iron •Not very shiny •poor conductors of heat and electricity •not ductile •not malleable •lower melting points and densities •C -carbon •O -oxygen •S -sulfur •H -hydrogen •N -nitrogen colour odour taste density hardness solubility melting point boiling point Each chemical substance has a unique set of properties that distinguishes it from every other substance Chemical Symbols of the Elements C carbon Ca calcium P phosphorus Fe iron -ferrum Pb lead - plumbum Allotropes • Allotropes: Some elements occur in different forms due to the different chemical arrangement of their constituent atoms. Eg. Carbon: diamond graphite soot Buckminsterfullerene Allotropes • Allotropes: Some elements occur in different forms due to the different chemical arrangement of their constituent atoms. Eg. Carbon: diamond graphite soot (tiny graphite particles) Buckminsterfullerene Allotropes • Allotropes: Some elements occur in different forms due to the different chemical arrangement of their constituent atoms. Eg. Carbon: diamond graphite soot (tiny graphite particles) Buckminsterfullerene Usually one form is more stable at a given temperature and pressure. Consist of 2 or more elements joined together in fixed proportions to form new substances NaCl salt sodium chloride H20 water Atoms are joined together by chemical bonds. Formed by chemical reactions Can be broken down into their constituent elements by chemical reactions A compound has its own physical and chemical properties that are quite distinct from those of the elements themselves. Compounds Eg. Salt – a compound of sodium and chlorine + Sodium • Soft metal • Reacts violently with water Chlorine • Yellow gas • Molecules • Very poisonous Salt • Clear crystals • Hard but brittle • Used to flavour food Structures consisting of two or more atoms that are chemically bound together and behave as an independent unit. The atoms can be from the same element (eg. N2) or different elements (eg. H2O). Nitrogen, N2 Water, H2O Methane, CH4 Ammonia, NH3 Alcohol, CH3CH2OH Contain more than one substance elements and/or compounds They have a variable composition -are not pure A homogeneous mixture is a SOLUTION AIR - contains •elements nitrogen-N oxygen O •contains compounds carbon dioxide, water • An atom is a chemically indivisible particle of an element. Cannot be chemically created, destroyed or changed. (eg. H, O, C) • A molecule consists of two or more atoms chemically bonded together. The atoms can be from the same or different elements. (eg. H2O, C2H5OH) • An element contains atoms of only one type. Cannot be chemically decomposed. (eg. hydrogen, oxygen, carbon) • A compound is composed of more than one type of atom joined by chemical bonds. It always has the same elements combined in the same integer ratio. Its properties are different to those of the component elements. (eg. water, alcohol) • A mixture has different elements or compounds mingled together. The properties of the components are maintained. (eg. beer, martini) Definitions • Different allotropes of element are different chemical ways of bonding its component atoms. (eg. diamond vs graphite vs soot for carbon) • Different states of a substance are different physical ways of packing its component particles. (eg. water vs ice)