Chemistry

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Chemistry

• Chapter 5 Electrons in Atoms

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The development of a New Atomic Model The Wave
Description of Light Electromagnetic radiation
form of energy that exhibits wavelike behavior as
it travels through space (X rays, ultraviolet and
infrared light, microwaves, and radio
waves). Electromagnetic spectrum Wavelength (?)
distance from one point on a wave to the next
corresponding point. The unit is a distance unit
could be very small or very large. Frequency
(?) the number of waves that pass through a
given point in one second. The unit is a per
second (s-1) or hertz (Hz) c ? ? c is the speed
of light. All electromagnetic waves travel the
speed of light. 3.00 X 108 m/s Wavelength and
frequency are inversely proportional
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The Photoelectric Effect the emission of
electrons from a metal when light shines on the
metal.. This provides evidence for the particle
nature of an electron. A quantum the minimum
quantity of energy that can be lost or gained by
an atom. Plancks equation E h? E is the
energy in joules, ? is the frequency of the
radiation emitted, and h is Plancks constant. h
6.626 X 10-34 Js A photon is a particle of
electromagnetic radiation having no mass and
carrying a quantum of energy
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The Hydrogen-Atom Line-Emission Spectrum ground
state the lowest energy state of an
atom. excited state a state in which an atom
has higher potential energy than it has in its
ground state. Line-emission spectrum when a
narrow beam of emitted light is passed through a
prism, it is separated into a series of specific
frequencies (and wavelengths) of visible light..
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Continuous spectrum the emission of a
continuous range of frequencies of
electromagnetic radiation. (white light through a
prism) When an excited atom with energy E2 ,
falls back to energy E1, it releases a photon
that has energy E2 E1 Ephoton hv Bohr
Model of the Hydrogen Atom Niels Bohr proposed a
model of the hydrogen atom that linked the atoms
electrons photon emission. Bohr proposed that
electrons orbit the nucleus at specific orbits.
When the atom becomes excited, electrons move to
a higher energy level (higher orbit). Upon
returning to the ground state, a specific
frequency of light is released..
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The Quantum Model of the Atom The Schrödinger
Wave Equation laid the foundation for modern
quantum theory. Quantum theory describes the wave
properties of electrons and the probability of
locations of electrons. Orbitals three
dimensional region around the nucleus that
indicates the probability of the location of an
electron.
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Atomic Orbitals and Quantum Numbers Quantum
Numbers specify the properties of atomic
orbitals and the properties of electrons in
orbitals. Principle Quantum Number symbolized
by n, indicates the main energy level occupied by
the electron. n 1 is the lowest energy level n
2 is the second energy level and so on. Angular
momentum quantum number l (more commonly known
as sublevels) indicate the shape of orbital.
There are 4 sublevels s, p, d, and f. each
becoming increasingly complex in arrangement. s
l 0 p l1 d l2 f l3
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Spin Quantum Number -2 electrons are found in
each orbital. The spin quantum number values are
½ or -½ indicating the two fundamental states of
an electron in an orbital
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• Electron Configuration arrangement of electrons
  in an atom
• Rules governing electron configuration
• Aufbau principle an electron occupies the
  lowest energy orbital that can receive it.
• 1s 2s 2p 3s 3p
• Pauli exclusion principle no two electrons in
  the same atom can have the same set of four
  quantum numbers an orbital can hold two
  electrons of opposite spin.
• Hunds rule orbitals of equal energy are each
  occupied by one electron before any orbital is
  occupied by a second electron, and all electrons
  in singly occupied orbitals must have the same
  spin.

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Representing Electron Configurations - Orbital
Notation
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1s22s22p63s23p64s23d104p65s24d105p66s24f145d10
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• Writing electron configurations
• strategy start with hydrogen, and build the
  configuration one electron at a time (the Aufbau
  principle  )
• Fill subshells in order by counting across
  periods, from hydrogen up to the element of
  interest

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examples Give the electron configurations for
Al Fe Ba Hg watch out for d f block
elements orbital interactions cause exceptions
to the Aufbau principle half-filled and
completely filled d and f subshells have extra
stability
1s22s2sp63s23p1
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Know these exceptions to the Aufbau principle in
the 4th period. (There are many others at the
bottom of the table, but don't worry about them
now.)
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• S 1s22s22p63s23p4
• Ne 3s23p4
• 2. W 1s22s22p63s23p64s23d104p65s24d105p66s24f145d4
  
• Xe 6s24f145d4
• 3. Ga 1s22s22p63s23p64s23d104p1
• Ar 4s23d104p1
• 4. Cd 1s22s22p63s23p64s23d104p65s24d10
• Kr 5s24d10
• 5. Cl 1s22s22p63s23p5
• Ne 3s23p5

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