 # Chapter 5 The Structure of Atoms

Yüklə 447 b.
 tarix 28.07.2018 ölçüsü 447 b. • ## Three fundamental particles make up atoms: • ## 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 • ## Atomic number – Z

• Z = # protons
• A = # protons + # neutrons
• # protons = # electrons • ## Atoms of the same element but with different masses ## Isotopes: Example • ## 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 spectrum of Ne+ ions

• This is how scientists determine the masses and abundances of the isotopes of an element • ## Let’s calculate the atomic mass of Ne using the mass-spectrometry data • ## 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.
• ## The atomic weight of an element is the weighted average of the masses of its isotopes • ## Calculate the atomic weight of chromium • ## = 63.5 amu • ## 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) • c =   
• ## The speed of electromagnetic waves in vacuum has a constant value:

• c = 3.00108 m/s
• This is the speed of light
• Given the frequency of the electromagnetic radiation, we can calculate its wavelength, and vice versa • ## 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) • ## What is the energy of green light of wavelength 5200 Å? Dostları ilə paylaş:

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