Atomic Structure Lecture 1-2

Atomic structure

Fundamentals of Inorganic ChemistryLectures 1 & 2SCH 100Dr. E. [email protected]: Biochemistry Rm 11Evaluation2 CAT 20 marksPractical 10 marks (Rem. Lab coats)End of term Exam 70

SyllabusThe early theories of atomic structure: the fundamental particles of the atom; Rutherfords planetary modelThe Bohr theory of the atom; failure of the Bohr theory. Plancks quantization of energy The photoelectric effect; Qualitative treatment of the atomic orbitals (s, p d and f). The Aufbau Principle and the periodic table. Common oxidation states of the elements. SyllabusNaturally occurring and artificially made isotopes, and their applications. Atomic properties of the elementselectronegativity electron affinityionization energyChemical bonding ionic, covalent, metallic, coordinate

SyllabusHybridization of atomic orbitals and shapes of simple molecules and ions.

The nature of ionic and covalent compounds as influenced by the above factors. The mole concept and its application. General concepts of acids and bases - strong and weak acids and bases; pH calculations. Balancing of redox reactions.Inorganic ChemistryIs the custodian of all the elements known.Is concerned with theOccurrence of the elements in natureExtraction from natural sourcesThe reactions of the elements with other elements and compoundsSafety and application of the elements and/ or their compounds

Inorganic ChemistryIs related to the other divisions of chemistry Organometallic chemistry bridges inorganic and organic chemistry. It deals with compounds containing direct metal-carbon bonds.The study of the composition, properties, and transformations of matterChemistryInorganic ChemistryBioinorganic chemistry bridges biochemistry and inorganic chemistryEnvironmental chemistry includes the study of both inorganic and organic compounds.

Lecture Objectives At the end of this lecture you should be able todescribe the historical development of atomic structuredescried the nature of electrons, protons and neutronsexplain the Thomson model of the atomexplain Rutherford model of the atomdescribe the nature of electromagnetic radiationdiscuss the Bohr model and the atomic hydrogen spectrum

Atomic Structure460 BC Democritus develops the idea of atoms

He pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called AtomaATOMA (greek for indivisible)HISTORICAL DEVELOPMENT OF THE ATOMIC THEORY10

1808John Dalton1Suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them Atoms.John Dalton, A New System of Chemical Philosophy, 1808; reprinted with an introduction by Alexander Joseph, Peter Owen Limited, London, 1965.HISTORICAL DEVELOPMENT OF THE ATOMIC THEORY11Daltons Atomic Theory Elements are made of extremely small particles called atoms.Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.Atoms cannot be subdivided, created, or destroyed.Atoms of different elements combine in simple whole-number ratios to form chemical compounds.In chemical reactions, atoms are combined, separated, or rearranged.HISTORICAL DEVELOPMENT OF THE ATOMIC THEORYAccess to materials /Noteshttp://soma.ku.ac.ke

Log in using your user id and password provided by university.E.g I20/xyzabc/2011Enrollment key = sch100

1898Joseph John ThompsonFound from his cathode ray tube experiments that atoms could sometimes eject a far smaller negative particle which he called an electron.

The electrons came from the atoms making up the cathode. HISTORICAL DEVELOPMENT OF THE ATOMIC THEORY14Joseph John ThompsonThomson found out that the electrons were the same regardless of the metal he used for the cathode. Therefore he concluded they were part of the structure of all atoms.He calculated the ratio of their charge to their mass Charge/mass = 1.76 x 1011 C/kgRobert Millikan determined the charge of the electron Charge of electron, e = 1.602 x 10-19 CThomson calculated the mass of the electron to be Mass of electron, me = 9.109 x 10-31 kgHISTORICAL DEVELOPMENT OF THE ATOMIC THEORYThompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge like plums surrounded by pudding.

PLUM PUDDINGMODELHISTORICAL DEVELOPMENT OF THE ATOMIC THEORY16Ernest Rutherford, 1910

Oversaw Geiger and Marsden carrying out his famous experiment. They fired -particles (a type of naturally-occurring radiation consisting of positively charged helium atoms) at a piece of gold foil which was only a few atoms thick.They found that although most of them passed through. About 1 in 10,000 hit something and bounced right back.HISTORICAL DEVELOPMENT OF THE ATOMIC THEORY17

gold foilhelium nucleiThey found that while most of the -particles passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back.helium nucleiHISTORICAL DEVELOPMENT OF THE ATOMIC THEORY18The ProtonIn 1918, while Rutherford was performing his various experiments in the field of radioactivity, bombarding nitrogen gas with alpha particles, he noticed that one of the experimental results was a surge of hydrogen. He correctly deduced that the hydrogen atoms must have come from within the nitrogen atoms themselves, which would mean that there was something within all of these atoms which was divisible, the amount of which would determine what element the atom represented.The protonThe particle Rutherford isolated was the proton, which by itself constitutes the nucleus of a single hydrogen atom, though in this case it was ionized (missing its electron, thereby giving it a net positive charge), which Rutherford determined by exposing the resulting hydrogen to magnetic fields.

Rutherfords new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction.HISTORICAL DEVELOPMENT OF THE ATOMIC THEORY

21The NeutronBy James Chadwick in 1932.Last to be discovered due to its neutrality.Now the structure was complete (somewhat)See details of discovery in http://isaacmmcphee.suite101.com/the-discovery-of-the-neutron-a46060

ParticleCharge (e)Mass (amu)Proton (p)+1 1Neutron (n) Neutral1Electron (e-)-11/1836Fundamental particles1 atomic mass unit (amu) = 1.672621777(74)1027 kg1 electric charge (e) = 1.602176565(35)1019CNature of Electromagnetic radiationNiels Bohr, 1913

Studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.HISTORICAL DEVELOPMENT OF THE ATOMIC THEORY25Bohrs ModelNucleusElectronOrbitElectron orbits2626HELIUM ATOM+NN+--protonelectronneutronShellWhat do these particles consist of?27ATOMIC STRUCTUREthe number of protons in an atomthe number of protons and neutrons in an atomHe24Atomic mass = protons + neutronsAtomic number = No of protonsnumber of electrons = number of protons28ATOMIC STRUCTUREElectrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shella maximum of 2 electrons second shella maximum of 8 electrons third shella maximum of 8 electrons29ATOMIC STRUCTUREThere are two ways to represent the atomic structure of an element or compound;1.Electronic Configuration2.Dot & Cross Diagrams30ELECTRONIC CONFIGURATIONWith electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example;NNitrogen7142 in 1st shell 5 in 2nd shellconfiguration = 2 , 52 + 5 = 731ELECTRONIC CONFIGURATIONWrite the electronic configuration for the following elements;CaOClSiNa2040112381716351428B115a)b)c)d)e)f)2,8,8,22,8,12,8,72,8,42,32,632DOT & CROSS DIAGRAMSWith Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example;NitrogenNXXXXXXXN71433DOT & CROSS DIAGRAMSDraw the Dot & Cross diagrams for the following elements;OCl8171635a)b)OXXXXXXXXClXXXXXXXXXXXXXXXXXX34SUMMARY The Atomic Number of an atom = number of protons in the nucleus.

The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus.

The number of Protons = Number of Electrons.

Electrons orbit the nucleus in shells.

Each shell can only carry a set number of electrons.35This powerpoint was kindly donated to www.worldofteaching.com

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