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• soft and ductile when annealed

2.5 HEAT TREATING

2.6 PAUL JOHNSON NOTES FOR EGR 250

• These notes in this section were copied from Paul Johnson’s web site and placed here.

2.6.1 Atomic Bonding and Structure

2.6.1.1 - Atomic Structure

A.Fundamental Concepts

1.Atomic number - # of protons in nucleus 2.Atomic mass - sum of protons and neutrons

3.Atomic weight - weighted average of atomic masses of natural isotopes 4.Atomic mass unit (amu) - 1/12th the mass of 12C

5.Mole - Avogadro's Number (6.023 x 1023) units (atoms or molecules) of a substance B.Atomic Models

1.Bohr model

a.Quantized energy levels for electrons in atom b.Discrete (particle like) electrons in an orbital

c.Energy levels are negative with respect to zero energy for a free electron 2.Wave-Mechanical model

a.Wave is neither wave nor particle, but can act like either in certain situations b.Electron described as an electron 'cloud'

c.Energy levels divided into subshells with discrete states for each pair of electrons given by

quantum numbers

1.Principal quantum number n = 1, 2, 3, 4, 5, 6, 7 2.2nd quantum number, subshell, l = s, p, d, f

3.3rd quantum number, energy states in subshell, mi = 1(s), 3(p), 5(d), 7(f) 4.4th quantum number, spin moment, ms = +½, -½

d.Ground state - all electrons in atom filling lowest energy level states e.Valence electrons - electrons in highest energy shell in ground state