Atoms and Ions KEY QUESTIONS THE BIG PICTURE What is the structure of an atom What units do I use to count atoms What are the properties of atoms Remember structure affects function What is the connection between atoms microscopic and grams macroscopic Where are the electrons located What is the energy of an electron By the End of Today s Lecture You Should Know the mole atomic structure protons neutrons electrons atomic weights wavelength and frequency of light dual nature of light electronic transitions and line spectra Bohr model CH110 FA10 SAS 1 Overview Classifications of Matter Know the difference One atom of an element is the smallest indivisible quantity of that element CH110 FA10 SAS 2 History of Atomic Structure 1 The early Greek s postulated that matter is composed of atomos which they found to be 2 J J Thompson early 1900s did experiments with cathode rays and discovered 3 Millikan absolute of an electron 4 Becquerel Radioactivity experiments demonstrated matter has and parts CH110 FA10 SAS 3 The Modern View of Atomic Structure 1 Rutherford 1910 Scattering of particles by metal foil dense positively charged nucleus 2 Rutherford s Nuclear Atom A small but massive with electrons surrounding it Most of volume is mass and charge is in very small dense nucleus CH110 FA10 SAS 4 The Modern View of Atomic Structure An atom is almost entirely If the nucleus was the size of a pencil eraser the atomic diameter would be 1nm 10 9 m 10 1nm angstrom Atom Diameter 0 1 0 5 nm Nuclear diameter 10 5 nm Ratio of nuclear size to atomic radius 10 4 Carbon atom diameter 0 154 nm CH110 FA10 SAS 5 Atoms Elements and Isotopes For an atom of a given element the number of protons is and equal to the The number of neutrons is Two atoms with number of protons but number of neutrons are isotopes of the same element The mass number of an atom is equal to the sum of its and A neutral atom has the same number of and 35 Cl 17 37 Cl 17 p e n p e n CH110 FA10 SAS 6 Atoms and Ions Mass amu proton p 1 electron e or e 0 neutron n 1 charge An atom or group of atoms is called an ion Ions have the same and as their parent atom Ions gain or lose a number of equal to their charge 19 F 9 p e n 19 F 9 p e n CH110 FA10 SAS 39 K 19 p e n 7 The Mole and Avogadro s Number Mole Avogadro s Number Avogadro s Number connects the weight of a single atom molecule and the weight of a laboratory sized sample CH110 FA10 SAS 8 Atomic Mass and Molar Mass Atomic Mass Formula Weight Molar Mass Examples 1 atom of 16O has a mass of and 1 mol of 16O has a molar mass of 1 molecule of NaOH has a mass of and 1 mol of NaOH has a molar mass of CH110 FA10 SAS 9 The Atomic Mass Scale By Definition SI The mass of one atom of 12C The mass of one mole of 12C atoms The definition of Avogadro s Number Experimentally one atom of 12C weighs 1 992648x10 23 g How many amu in one g All other atomic masses are defined relative to the mass of 12C 1 atom of 1H weighs 1 6735x10 24 g 1 atom of 16O weighs 2 6560x10 23 g CH110 FA10 SAS 10 Practice Problem An unknown element is found to have three naturally occurring isotopes with atomic masses of 35 9675 0 337 37 9627 0 063 and 39 9624 99 600 Which of the following is the unknown element A B C D E Ar K Ca Cl None of these Average Atomic Weight Relative atomic mass average masses of isotopes Average atomic mass is also known as Atomic weight Atomic weights are listed on the periodic table CH110 FA10 SAS 11 Experiments to Probe Atomic Structure When atoms absorb energy they often emit light Light can undergo diffraction wave nature but also has momentum particle nature Several other phenomena are inconsistent with the wave nature of light Blackbody radiation Photoelectric effect Line spectrum of atoms The Photoelectric Effect What can the emitted light tell us about atomic structure CH110 FA10 SAS 12 Electromagnetic Radiation Light and other electromagnetic radiation behaves as a distance between maxima m maxima per second s 1 cycles s hertz Hz c speed of light in a vacuum on sheet c Light and other electromagnetic radiation behaves as a with kinetic energy E h Planck s Constant on sheet CH110 FA10 SAS 13 The Electromagnetic Spectrum CH110 FA10 SAS 14 Spectroscopy The Study of Light Interacting with Matter Spectrum Monochromatic Continuous Discrete or line only one all s a few s lasers hot solids gaseous atoms Observation of line spectra implies that atoms have discrete quantized energy levels CH110 FA10 SAS 15 Demo Line Spectra of the Group 1A Elements Why don t we observe a continuous spectrum What does the observations we make today tell us about the structure of the atoms we are observing Before Monday re read chapter 6 paying close attention to the Bohr model We will be discussing the theory behind today s demo then CH110 FA10 SAS 16 What You Should Know Introduction to Atomic Structure Approximate size of an atom Atomic components ions or neutral how many p e n what is atomic number Isotopes atomic number stays the same how many p e n Average Atomic Masses how to calculate Avogadro s number memorize What is molecular weight Calculate MW for a molecule Electromagnetism and Line Spectra What is the range of visible light Rank the following types of light in order of increasing uv ir visible microwave What is relationship between the wavelength and frequency of light Rank the following types of light in order of increasing uv ir visible microwave CH110 FA10 SAS 17