Download Energy and Matter - Hicksville Public Schools

Arrangement of Electrons in the Atom
Summarizing Key Concepts:
Radiant Energy:
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Light is a form of electromagnetic radiation. Its energy is transmitted in a form of waves.
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All waves can be described by their wavelength (), frequency (), amplitude, and speed. The
wavelength and the frequency are indirectly related to each other – when the wavelength is short, the
frequency is high and vise versa.
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The electromagnetic spectrum spans a wide range of wavelengths from radio (longest wavelength –
lowest frequency and lowest energy) to X-rays (shortest wavelength – highest frequency and highest
energy).
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In a vacuum, all electromagnetic waves travel at a speed of 3.00 x 10 8 m/sec.
Quantum Theory:
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All electromagnetic waves have dual nature and may be described as both waves and particle. Particles
of light are called photons.
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Energy is emitted or absorbed by matter in quanta – specific amounts.
Another Look at the Atom:
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When sunlight (visible, white light) is passed through a prism, the resulting visible spectrum is the
continuous spectrum – shows all the colors of the ROYGBIV.
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In contrast to the continuous spectrum produced by white (visible) light, when a sample of an element
is heated and the emitted light is passed through a prism, a bright-line spectrum is observed.
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An element’s atomic emission spectrum consists of a series of fine lines of individual colors – known
as the bright-line spectrum.
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The Bohr model proposes that the energy of electrons is quantized (allowed only in specific amounts)
and electrons spin in specific orbits, each with a different amount of energy, around the nucleus.
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Electrons enter the lowest energy level that is available to them - the ground state. Upon absorbing
energy, electrons move to higher energy levels - the excited state.
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The excited state is short living. According to the Bohr model of the atom, hydrogen’s atomic
emission spectrum = bright line spectrum, results from electrons dropping from higher-energy atomic
orbits (excited state) to lower-energy atomic orbits (ground state).
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The Heisenberg uncertainty principle states that it is impossible to know precisely the velocity
(momentum) and the location (position) of a particle at the same time.
A New Approach to the Atom:
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The quantum mechanical model (cloud or Schrödinger model) of the atom explains the properties of
atoms by treating the electron as a wave and by including the idea of quantized energies.
Electrons occupy atomic orbitals. An orbital is a region in the space around the atom’s nucleus where
an electron with a particular amount of energy can be found 90% of the time. An orbital may occupy
up to two electrons spinning in opposite spins.
Principle energy levels consist of sublevels such as s,p,d, and f. Each sublevel contains a different
number of orbitals. 1orbital in the s sublevel, 3 orbitals in the p sublevel, 5 orbitals in the d sublevel,
and 7 orbitals in the f sublevel. The shape of the orbital depends on the sublevel – an orbital in the s
sublevel has a spherical shape while – an orbital in the p sublevel has a dumbbell shape.
Electrons Configuration and Notation:
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The arrangement of electrons in the atom is called the atom’s electron configuration. Electron
configurations are prescribed by three rules: the aufbau principle – states that in the ground state
electrons occupy the lowest energy orbitals available, the Pauli exclusion principle – states that only
up to 2 electrons can occupy an orbital, and the Hund’s rule – describes how electrons fill orbitals of
equal energy so that a maximum number of unpaired electrons results.
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Electrons related to the atom’s highest principle energy level are referred to as valance electrons.
Valence electrons determine the chemical properties of an element.
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Electron configuration may be represented using orbital diagrams (arrows), electron configuration
notation, noble-gas electron configuration, and Lewis-dot diagrams for valence electrons.
Key Equations and Relationships:
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Electromagnetic wave relationship:
c =  x ν (c = speed of light,  = wavelength, and ν = frequency).
 =
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c

and

=
c

Energy of a quantum or a photon:
Equantum(photon) = h x ν (E = energy, h = Plank’s constant, and ν = frequency).
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Energy change of an electron: ∆E = E
higher energy level
-E
lower energy level
Vocabulary:
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amplitude
atomic emission spectrum
(bright-line spectrum)
atomic orbital
aufbau principle
electromagnetic radiation
electromagnetic spectrum
electron configuration
electron-dot diagram
energy sublevel
excited state
frequency
ground state
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Heisenberg’s uncertainty principle
Haund’s rule
Pauli exclusion principle
Photon
Plank’s constant (6.626 x 10-34 J x Sec)
Principle energy level
Principle quantum number
Quantum
Quantum mechanical model of the atom
Speed of light in vacuum (3.00 x 108 m/sec)
Valence electrons
Wavelength