Download CHEMISTRY 30A CHAPTER 2 NOTES FALL 2014

CHEMISTRY 30A
LANEY COLLEGE
CHAPTER 2 NOTES
FALL 2014
Atomic structure: nucleus + electrons
Nucleus: protons + neutrons
Proton, mass = 1 dalton; charge = +1
Neutron, mass = 1 dalton; charge = 0
Atomic number = number of protons in nucleus
Atomic weight = number of protons + neutrons
ISOTOPE: same number of protons, different number of neutrons
Charge on an atom: number of protons minus number of electrons; a neutral atom has the
same number of electrons and protons. An atom with unequal numbers of protons and
neutrons is called an ION. Example: The Na+ ion has 11 protons in the nucleus
(obviously!) and 10 electrons in the orbitals surrounding the nucleus.
Electrons and electronic configuration
Electrons occupy orbitals. An orbital is a probability distribution function that defines the space
where an electron has the highest probability of being found, if one could actually find an electron. The
probability that a given electron is somewhere is 100% but that is not helpful. An orbital is usually
defined as a space within which one is 95% likely or 99% likely to find the electron.
Although the space within which the electron has a high probability of being found is fuzzy, the
energy associated with a particular orbital is very exact. Electronic energy levels are quantized, meaning
that each orbital is associated with a very specific energy. It is like climbing a flight a stairs. One must
ascend the staircase one step at a time, or jump two steps or three or four steps at a time but going up 1.5
stairs is impossible/not allowed/forbidden.
Heisenberg Uncertainty Principle: you can only know where the electron was; by the time you
locate it, it is somewhere else.
The four Quantum numbers
Principal (1,2,3…) quantum number defines the shell, first, second, third, etc.
Secondary quantum number (s, p, d, f) defines the subshell and specifies the 3D shape of the orbital.
Spatial orientation quantum number: s, only 1 possible orientation (spherical symmetry); p, 3 possible
nonequivalent spatial orientations; d, 5 possible, nonequivalent spatial orientations; f, 7 possible
nonequivalent spatial orientations.
Spin: up arrow or down arrow (two possibilities)
The Exclusion Principle: no two electrons of an atom may have the same 4 quantum numbers. And there
are only two electrons permitted per orbital.
Electronic configuration: building up the atom, any atom. See text. Pp 61-62. Be prepared to
provide the electronic configuration of any atom in the first four rows of the periodic table, given the
atomic number and the charge on the atom. (Be aware that the +3 ion of chromium, for example, has 24 3 = 21 electrons to account for).
CHEMISTRY 30A
LANEY COLLEGE
CHAPTER 2 NOTES
FALL 2014
The Periodic Table
Main groups, transition metals, s-block, p-block, d-block, f-block.
Alkali metals (Group 1A); alkaline earth metals (Group 2A), halogens (Group VIIA), noble gases (Group
8A), transition metals (partially filled 3d subshell).
The chemical properties of an atom are determined by its outer-shell electrons. There is a tremendous
stability associated with a filled shell or, to a lesser extent, a filled subshell, or, to a still lesser extent, a
half-filled subshell. Much of the chemistry of the elements can be explained by the drive to assume the
most energetically favorable electronic configuration. For example, the neutral sodium atom does not
exist in nature; it exists only as the Na+ ion (1s2 2s2 2p6). In other words, the chemistry of sodium can be
summed up simply: sodium has a really awesome tendency to lose its 3s electron so as to assume an
electronic configuration consisting of filled shells 1 and 2. Not coincidentally, this is the same electronic
configuration as the inert neon atom. (Here is a succinct description of the chemistry of neon: nada. Here
is a succinct description of the chemistry of the Na+ ion: nada).
Electron-Dot Symbols
Since all those inner-shell electrons count for naught, why not just write the symbol of the element with
dots representing its outer-shell electrons? Thus, Na∙ or Mg: etc. Exercise for the reader: give electron dot
formulas for C, S, P, and Br.
The Electromagnetic Spectrum
In addition to proton, neutron and electron, we should add photon. The photon behaves as a wave rather
than a particle and interacts with matter on the quantum level. Waves listed in order of decreasing energy
go from gamma rays and X-rays (high energy) through UV, visible light, infrared and microwave
radiation to radio waves (low energy). Light from the sun and other sources is delivered as discrete
particles (waves) defined in terms of wavelength or energy. The greater the wavelength, the lower the
energy. Radio waves are at the long wavelength end of the spectrum, are of the lowest energy, and do not
interact with living tissue. Gamma rays and X-rays, on the other hand, destroy living tissue because, on a
quantum level, their energies match with the energies holding together the atoms of protein and so break
those bonds between the atoms of protein.
There is no quantum match between microwave radiation and protein and so this chemist thinks concern
over the possible hazards of exposure to low-level microwave radiation is bull-bleep.
Final Thoughts
Energy is conserved. Mass is conserved. Charge is conserved (don’t forget charge!). Exception: under
extraordinary conditions, mass can be converted to energy as in E = mc2.