Components and Structure of the Atom Chemistry 142 A James B. Callis, Instructor Winter Quarter, 2006 Lecture #5.

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Presentation transcript:

Components and Structure of the Atom Chemistry 142 A James B. Callis, Instructor Winter Quarter, 2006 Lecture #5

Neon Signs Low pressure neon gas in evacuated tube, between electrodes. High voltage separates +, - charges in Ne atoms: + particle goes to - electrode. - particle goes to + electrode. Measure current between electrodes: Shows atoms made of +, - charges.

Movies to Illustrate the Nature of Atoms Primitive Cathode Ray Tube: Millikan Oil Droplet Experiment: Rutherford Scattering Experiment: htm&url= erford/

Deflection -> mass/charge

Millikan’s Experiment 1. Measured rate of droplet’s fall without voltage: gave its mass. 2. Voltage across plates influenced speed, due to charge of droplet. 3. Quantitative effect of voltage w/ laws of physics -> amt. of charge on droplet. 4. RESULT: Different droplets had different charge, but always a multiple of same number -> elementary charge on electron: e = 1.602x coulombs (negative). 5. (Mass/charge) x e - = mass of e -

Rutherford Experiment Alpha (i.e., subatomic) particles bombarding the atom. Rationale - to study the internal structure of the atom, and to know more about the mass distribution in the atom. Bombarded a thin Gold foil with alpha particles from radium.

Ernest Rutherford ( ) Won the Nobel Prize in Chemistry in 1908 “It was quite the most incredible event..... It was almost as if a gunner were to fire a shell at a piece of tissue and the shell bounced right back! ”

The Neutron Protons cannot be the only particle in the nucleus because the mass of the protons in is less than the mass of the nucleus. Therefore, a third, neutrally charged particle must exist! James Chadwick discovered the missing subatomic particle, the neutron. He bombarded beryllium foil with alpha particles and noticed a neutral stream of particles coming out. The particles have about the same mass as a proton.

Notes: mass of e - tiny relative to p +, n. p +, n have same mass (almost). e-, p + have same charge, opposite sign.

Moving electron cloud surrounding nucleus. Almost all the mass in the nucleus. Radius of Atom = ~10 -8 cm Diameter of Nucleus = ~ cm __________________ Diameter = cm

Atomic Definitions I: Symbols, Isotopes,Numbers X A Z X = Atomic symbol of the element, or element symbol A = The Mass number; A = Z + N Z = The Atomic Number, the Number of Protons in the Nucleus (All atoms of the same element have the same no. of protons.) N = The Number of Neutrons in the Nucleus Isotopes = atoms of an element with the same number of protons, but different numbers of Neutrons in the Nucleus The Nuclear Symbol of the Atom, or Isotope

Neutral ATOMS 51 Cr = p + ( ), e - ( ), n ( ) 239 Pu = p + ( ), e - ( ), n ( ) 15 N = p + ( ), e - ( ), n( ) 56 Fe = p + ( ), e - ( ), n ( ) 235 U =p + ( ), e - ( ), n ( ) If neutral, then number of electrons = number of protons. Numbers of each particle:

For each of the following ions, indicate the total number of protons and electrons and neutrons in the ion. (a) 127 I - (c) 27 Al +3