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Chapter 5 The Structure of Atoms
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tarix | 28.07.2018 | ölçüsü | 0,89 Mb. | | #59357 |
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CHAPTER 5
Fundamental Particles Three fundamental particles make up atoms:
The Discovery of Electrons Late 1800’s & early 1900’s Cathode ray tube experiments showed that very small negatively charged particles are emitted by the cathode material.
The Discovery of Electrons
Rutherford’s Atom - The atom is mostly empty space
- It contains a very small, dense center called the nucleus
- Nearly all of the atom’s mass is in the nucleus
- The nuclear diameter is 1/10,000 to 1/100,000 times less than atom’s radius
The Discovery of Protons
The Discovery of Neutrons
Mass number – A Atomic number – Z - Z = # protons
- A = # protons + # neutrons
- # protons = # electrons
Atoms of the same element but with different masses
Isotopes: Example
Experimental Detection of Isotopes Factors which determine a particle’s path in the mass spectrometer: - accelerating voltage, V
- magnetic field strength, H
- mass of the particle, m
- charge on the particle, q
Mass Spectrometry & Isotopes Mass spectrum of Ne+ ions - This is how scientists determine the masses and abundances of the isotopes of an element
Mass Spectrometry & Isotopes Let’s calculate the atomic mass of Ne using the mass-spectrometry data
Atomic Weight Scale A unit of atomic mass (atomic mass unit) was defined as exactly 1/12 of the mass of a 12C atom Two important consequences of such scale choice: - The atomic mass of 12C equals 12 a.m.u.
- 1 a.m.u. is approximately the mass of one atom of 1H, the lightest isotope of the element with the lowest mass.
Isotopes and Atomic Weight Naturally occurring chromium consists of four isotopes. It is 4.31% 50Cr, mass = 49.946 amu 83.76% 52Cr, mass = 51.941 amu 9.55% 53Cr, mass = 52.941 amu 2.38% 54Cr, mass = 53.939 amu Calculate the atomic weight of chromium
Isotopes and Atomic Weight Naturally occurring Cu consists of 2 isotopes. It is 69.1% 63Cu with a mass of 62.9 amu, and 30.9% 65Cu, which has a mass of 64.9 amu. Calculate the atomic weight of Cu to one decimal place. A.W.(Cu) = (62.9 amu 0.691) + ( 64.9 amu 0.309) = = 63.5 amu
Electromagnetic Radiation Any wave is characterized by 2 parameters: - Wavelength () is the distance between two identical points of adjacent waves, for example between their crests
- It is measured in units of distance (m, cm, Å)
- Frequency () is the number of wave crests passing a given point per unit time (for example, per second)
- It is measured in units of 1/time, usually s-1
- 1 s-1 = 1 Hz (Hertz)
Electromagnetic Radiation The speed at which the wave propagates: The speed of electromagnetic waves in vacuum has a constant value: - c = 3.00108 m/s
- This is the speed of light
- Given the frequency of the electromagnetic radiation, we can calculate its wavelength, and vice versa
Electromagnetic Radiation Electromagnetic radiation can also be described in terms of “particles” called photons Each photon is a particular amount of energy carried by the wave Planck’s equation relates the energy of the photon to the frequency of radiation: - E = h
- (h is a Planck’s constant, 6.626·10-34 J·s)
Electromagnetic Radiation What is the energy of green light of wavelength 5200 Å?
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