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ATOMS: THE BUILDING BLOCKS OF MATTER EARLY HISTORY OF CHEMISTRY Leucippus, Democritus World is made of ________________________________________ (Greek – Atomos; indivisible) Aristotle Matter was ________________________________ Matter does not consist of smaller particles Before 16th century Alchemy: Attempts (scientific or otherwise) to __________________________ 17th century First “chemist” to perform quantitative experiments Published “The Skeptical Chymist” Definition of elements became generally accepted 18th century ________________ Phlogiston flows out of a burning material ________________ Discovered oxygen and was found to support combustion Antoine Lavoisier Law of Conservation of Mass: ___________________________________________ Combustion involves oxygen, not “phlogiston” Joseph Proust Law of Definite Proportion: _____________________________________________ ___________________________________ ______________________ Invention of a simple set of symbols for the elements, along with system of writing formulas and compounds Discovered elements Cerium, Thorium, Selenium, and Silicon John Dalton (1808) Proposed an explanation for the law of conservation of mass, law of definite proportion and law of multiple proportion Postulates of Dalton’s Theory All matter is Atoms Atoms of a given element are Atoms of different elements combine in In chemical reactions, atoms are LAW OF MULTIPLE PROPORTION Atoms of different elements combine in simple whole number ratios to form chemical compounds Not all aspects of Dalton’s atomic theory have proven to be correct Dalton’s atomic theory have been modified All matter is composed of atoms, which are ____________________________________ A given element can OSHIKIRI / Chemistry 1 of 8 STRUCTURE OF THE ATOM J. J. Thomson (Cathode Ray Research 1897) Cathode rays consist of small negatively charged particles called electrons J. J. Thomson (Cathode Ray Research 1897) Electrons are like raisins dispersed in a pudding (the positive charge cloud) Robert Millikan (Oil Drop Experiment, 1909) Determined the charge of the electron and confirmed that the electron carry negative charge Calculated mass of electron: 1/1840 mass of hydrogen atom (9.11 x 10-31 kg) GOLD FOIL EXPERIMENT (1911) – By Ernest Rutherford, Hans Geiger, & Ernest Marsden A thin sheet of gold foil was bombarded with Most of the alpha particles passed straight through Many particles were GOLD FOIL EXPERIMENT – Conclusions Most of the alpha particles passed directly through the foil because the atom is The deflected alpha particles are those that had a NUCLEAR ATOM MODEL An atom with a THE NUCLEUS PROTONS Positively charged subatomic particle Discovered a beam consisting of positive particles called “protons” using a modified cathode ray tube J. J. Thomson Protons have the same amount of electrical charge as an electron but opposite in charge (+1) Calculated the mass of proton – 1840 times that of electron Mass of proton : 1.673 x 10 –27 kg NEUTRONS Subatomic particles with no charge James Chadwick (1932) Uncharged particles with a mass slightly greater than protons were formed when Beryllium was bombarded with high-energy alpha particles Named it neutron Mass: 1.675 x 10-27 kg NUCLEAR FORCE Short-range proton-neutron, proton-proton, proton-neutron force that holds the nuclear particles together Nucleus has a high density – 2 x 108 metric tons/cm3 OSHIKIRI / Chemistry 2 of 8 NUCLEUS Located near the center of the atom Has a positive charge Occupies a very small part of the atom Has very high density Composed of protons and neutrons ELECTRON CLOUD Region occupied by electrons Cloud of negative charge Surrounds the nucleus of the atom Occupy most of the volume of the atom OTHER SUBATOMIC PARTICLES LEPTON (light) HADRONS (heavy) Baryons – Mesons – quarks, antiquarks Quarks: Up, down, charm, strange, bottom, top Quarks are held together by gluons Murray Gell-Mann discovered quarks ANTIPARTICLES EX: electron (-) and positron (+) SIZES OF ATOMS Atomic Radius Distance from the Atomic radii range from FORCES IN ATOMS GRAVITY Carried by Graviton WEAK w + w - z0 ELECTROMAGNETIC Photon STRONG Gluon Acts on OSHIKIRI / Chemistry 3 of 8 COUNTING ATOMS Atomic Number (Z) Number of Determines the identity of the element Henry Moseley (1913) Studied X-rays produced in X-ray tubes with X-ray wavelength depend on Determined the Mass Number (A) Total number of protons and neutrons in the nucleus of the atom (Rounded-off atomic mass) Atomic Mass - mass of protons, neutrons and electrons in a single atom (when the atom is motionless) ISOTOPES Atoms of the same element that have the Usually identified by specifying the mass number (hyphen notation) Carbon-12, Carbon-14, Uranium-235, Uranium-238 Sodium-23, Sodium-24 Hydrogen-1, Hydrogen-2, Hydrogen-3 Nuclide General term for Nuclear Symbol Shows the composition of the nucleus EXAMPLES: PROTONS, NEUTRONS, & ELECTRONS Atomic # = Mass # = # Neutrons = Identify elements using atomic # Mass numbers of elements CAN change but Atomic numbers will always be the same OSHIKIRI / Chemistry 4 of 8 Protons, Neutrons, & Electrons Nuclide Symbol Atomic Mass # of p+ number number # of n0 # of e- Aluminum-27 108 47 25 9 4 Iodine-131 Be 9 30 4 53 RELATIVE ATOMIC MASSES Carbon-12 Nuclide Standard used for units of atomic mass Atomic Mass Unit (amu) 1/12 the mass of a carbon-12 atom Mass Spectrometer Instrument used to determine the relative atomic mass of atoms by the deflection of their ions on a magnetic field Average Atomic Mass Weighted average reflects both the ___________ and the _______________________ of the isotopes as they occur in nature AveAtomicM ass (% abundance A AtMass A ) (% Abundance B AtMass B ) 100 63 65 Cu Cu 29 The element copper is found to contain the naturally occurring isotopes and 29 . The relative abundances are 69.1% and 30.9% respectively. Calculate the average atomic mass of copper. 36 38 40 Ar Ar Ar Three isotopes of argon occur in nature – 18 , 18 , and 18 . Calculate the average atomic mass of argon to two decimal places given the following relative atomic masses of each of the isotopes” argon-36 (35.97 amu; 0.337%), argon-38 (37.96 amu; 0.063%), and argon-40 (39.96 amu; 99.600%). OSHIKIRI / Chemistry 5 of 8 Gallium has two naturally occurring isotopes, Ga-69 and Ga-71, with masses of 68.9257 amu and 70.9249 amu. Calculate the percent abundances of these isotopes of gallium. MASS, MOLE & MOLAR MASS Mole (mol) Amount of substance that contains as many particles as there are in 12 g of carbon-12 Avogadro’s Number (6.022 x 1023units) Number of particles in exactly one mole of a pure substance Units can be Molar Mass (g/mol) Mass in It is equal to the atomic mass of the element Examples Carbon – 12.01 g/mol (1mol C=12.01 g) Neon – 20.18 g/mol (1 mol Ne = 20.18 g) GRAM/MOLE CONVERSIONS 1 mol = Molar Mass in grams (Atomic Mass) 1 mol = 6.022 x 1023 atoms MOL TO GRAM What is the mass in grams of 3.50 mol of the element Silicon, Si? GRAM TO MOL A chemist produced 15.0 g of aluminum, Al. How many moles of aluminum were produced? ATOMS TO MOL How many moles of silver, Ag, are in 3.01 x 1023 atoms of silver? MOL TO ATOMS How many atoms of Nickel, Ni, are in 5.00 mol of Ni? OSHIKIRI / Chemistry 6 of 8 ATOMS TO MASS What is the mass in grams of 7.50 x 1015 atoms of Zinc, Zn? MASS TO ATOMS How many atoms of sulfur, S, are in 12.5 g of sulfur? THE PERIODIC TABLE GROUPS OR FAMILIES Elements in the same group have the same properties PERIODS OR SERIES TYPES OF ELEMENTS _____________ – elements that are hard and shiny, good conductors of heat and electricity _____________ – elements that are non-lustrous, brittle, and poor conductors of heat and electricity _____________ – elements that border the zigzag line in the periodic table Have some characteristics of both metals and nonmetals _____________ – elements of Group 18 which are generally unreactive OSHIKIRI / Chemistry 7 of 8 OSHIKIRI / Chemistry 8 of 8