Presentation on theme: "Chemistry Chapter 3 Atoms: The Building Blocks of Matter."— Presentation transcript:
1Chemistry Chapter 3Atoms:The BuildingBlocks of Matter
2Law of Conservation of Mass Mass is neither created nor destroyed during chemical or physical reactions.Total mass of reactants=Total mass of productsAntoine Lavoisier
3Dalton’s Atomic Theory (1808) All matter is composed of extremely small particles called atomsAtoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other propertiesJohn DaltonAtoms cannot be subdivided, created, or destroyedAtoms of different elements combine in simple whole-number ratios to form chemical compoundsIn chemical reactions, atoms are combined, separated, or rearranged
4Modern Atomic TheorySeveral changes have been made to Dalton’s theory.Dalton said:Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other propertiesModern theory states:Atoms of an element have a characteristic average mass which is unique to that element.
5Isotopes Elements occur in nature as mixtures of isotopes. Isotopes are atoms of the same element that differ in the number of neutrons
6Composition of the nucleus Atomic MassesAtomic mass is the average of all the naturally isotopes of that element.Carbon =IsotopeSymbolComposition of the nucleus% in natureCarbon-1212C6 protons6 neutrons98.89%Carbon-1313C7 neutrons1.11%Carbon-1414C8 neutrons<0.01%
7Modern Atomic Theory #2 Dalton said: Atoms cannot be subdivided, created, or destroyedModern theory states:Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions!
8Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle.Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
10Thomson’s Atomic Model Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.
11Mass of the Electron1909 – Robert Millikan determines the mass of the electron.The oil drop apparatusMass of the electron is9.109 x kg
12Conclusions from the Study of the Electron Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electronsElectrons have so little mass that atoms must contain other particles that account for most of the mass
13Rutherford’s Gold Foil Experiment Alpha particles are helium nucleiParticles were fired at a thin sheet of gold foilParticle hits on the detecting screen (film) are recorded
14Try it Yourself!In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?
16Rutherford’s Findings Most of the particles passed right throughA few particles were deflectedVERY FEW were greatly deflected“Like howitzer shells bouncing off of tissue paper!”Conclusions:The nucleus is smallThe nucleus is denseThe nucleus is positively charged
17Atomic Particles Particle Charge Mass (kg) Location Electron -1 9.109 x 10-31Electron cloudProton+11.673 x 10-27NucleusNeutron1.675 x 10-27
18The Atomic ScaleMost of the mass of the atom is in the nucleus (protons and neutrons)Electrons are found outside of the nucleus (the electron cloud)Most of the volume of the atom is empty space“q” is a particle called a “quark”
20About Quarks… Protons and neutrons are NOT fundamental particles. Protons are made of two “up” quarks and one “down” quark.Neutrons are made of one “up” quark and two “down” quarks.Quarks are held togetherby “gluons”
21Atomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.Element# of protonsAtomic # (Z)Carbon6Phosphorus15Gold79
22Isotopes…Again (must be on the test) Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.IsotopeProtonsElectronsNeutronsNucleusHydrogen–1(protium)1Hydrogen-2(deuterium)Hydrogen-3(tritium)2
23Mass Number Nuclide p+ n0 e- Mass # Mass number is the number of protons and neutrons in the nucleus of an isotope.Mass # = p+ + n0Nuclidep+n0e-Mass #Oxygen -10-3342- 3115188818Arsenic753375Phosphorus161531
24The Mole 1 dozen = 12 1 gross = 144 1 ream = 500 1 mole = 6.02 x 1023 There are exactly 12 grams of carbon-12 in one mole of carbon-12.
25I didn’t discover it. Its just named after me! Avogadro’s Number6.02 x 1023 is called “Avogadro’s Number” in honor of the Italian chemist Amadeo Avogadro ( ).I didn’t discover it. Its just named after me!Amadeo Avogadro
26Calculations with Moles: Converting moles to grams How many grams of lithium are in 3.50 moles oflithium?3.50 mol Li6.94 g Li= g Li45.11 mol Li
27Calculations with Moles: Converting grams to moles How many moles of lithium are in 18.2 grams oflithium?18.2 g Li1 mol Li= mol Li2.626.94 g Li
28Calculations with Moles: Using Avogadro’s Number How many atoms of lithium are in 3.50 moles oflithium?3.50 mol Li6.022 x 1023 atoms Li= atoms Li2.11 x 10241 mol Li
29Calculations with Moles: Using Avogadro’s Number How many atoms of lithium are in 18.2 g oflithium?18.2 g Li1 mol Li6.022 x 1023 atoms Li6.94 g Li1 mol Li(18.2)(6.022 x 1023)/6.94= atoms Li1.58 x 1024