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Bohr’s ATOM
Atom
HELIUM
Refining Nuclear Models
• In 1913, Danish physicist, Niels Bohr, refined Rutherford's idea by adding that the electrons were in orbits around the nucleus. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.
a set number of electrons.
• He proposed a Bohr model or Orbit model
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_________
+
-
N
N
+
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The Bohr Model
• 1. Electrons revolve around the nucleus in specific orbits (shells), or energy levels.
• 2. An atom has energy levels. Electrons can only exist in these energy levels, not in between.
• 3. When an atom is in the ground state, the electrons exist in the energy levels closest to the nucleus. • 4. If an atom receives, energy, the atom becomes excited and electrons jump to higher energy levels.
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Ground State
• The lowest energy state of an atom
• Electrons in the first energy level have the lowest potential energy since they are located closest to the nucleus.
http://www.visionlearning.com/library/flash_viewer.php?oid=1347&mid=51
Excited State
• An atom has a higher potential energy than in the ground state because electrons have “jumped”
(moved up) to a higher energy level. • Electrons with higher potential energy occupy orbits farther from the nucleus The further an electron is
farther from the nucleus. The further an electron is from the nucleus, the greater its energy! • Atom song:
• http://www.youtube.com/watch?v=vUzTQWn
‐wfE&feature=related
• Build an atom:
ild
• http://www.classzone.com/books/earth_scien
ce/terc/content/investigations/es0501/es0501
page03.cfm
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Current Atomic Model
• Electrons act like particles (because they have a mass) and waves (because they have certain frequencies corresponding to their energy levels)
• Electrons are located in orbitals around the nucleus that correspond to specific energy levels
• Electron clouds = orbitals that do not have sharp boundaries, but p
,
shows 3D region where electrons are most probable to be found.
• Electron Cloud Model or Quantum Model proposed by Louis de Broglie & Erwin Schrodinger Classify the following as ground state electron
configurations or excited state electron configurations.
Element
ground state electron configurations or
excited state electron configuration
lithium
1-2
calcium
2-8-7-3 excited
chlorine
2 8 7
2-8-7
aluminum
2-7-4
excited
neon
2-7-1
excited
sodium
2-8-1
ground
potassium
2-8-7-2 excited
exited
Electron Configuration
• Arrangement of electrons
• Each atom has a distinct electron configuration.
• The ground state electron configuration is found on the periodic table in the lower left hand corner of each box.
The configuration listed on the periodic table is the ground state electron configuration. In the chart below, draw the ground state and excited state electron configurations Element
Ground State
Excited State
He
ground
O
Na
F
Al
Mg
Br
Element
Ground State
Electron
Configuration
Ion
Na
Na +
Mg
Mg +2
Fe
Fe +3
Al
Al +3
Li
Li +1
Ion’s Electron
Configuration
Quantum
• Electrons can only absorb or release energy in discrete, specific amounts. • The amounts, or bundles of energy are called quanta (or photons) corresponding to differences in energy levels of the
differences in energy levels of the orbitals/shells.
• The greater the radius of an orbit (the farther from the nucleus), the greater the energy of the electrons in that orbit. The orbits or shells are known as principal energy levels. 2
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Electrons and Light
Light Emission
• An atom emits energy when the electron falls from high energy levels to lower energy levels. This energy is in the form of electromagnetic radiation.
• If the wavelength is in the visible light spectrum, the energy can be seen as color.
gy
• Each move from a particular energy level to a lower energy level will release light of a specific wavelength.
• When certain elements are excited, they give yg
off energy of a distinctive color as the electron fall back down to lower energy levels. These colors are specific and can be used to identify the elements (Flame Test).
Spectroscopic analysis of the visible spectrum…
…produces all of the colors in a continuous spectrum
Spectral lines
• If high voltage is applied to hydrogen gas confined in a gas tube, called a gas discharge tube, light is emitted. If this light is passed through a prism, a series of bright lines of distinct colors is produced. Bohr reasoned that these different colored bands of light were actually quanta of corresponding energy. These quanta were emitted as electrons of hydrogen atoms returned from their higher levels in the excited state to their lower levels in the ground state.
…produces a “bright line” spectrum
Valence Electrons
Bright Line Spectra
• Bright line spectrum = the series of bright lines produced when excited electrons return to their original energy levels
original energy levels • Each element has its own unique set of spectral lines which can therefore be used to identify the elements presence.
Electrons that occupy the valence energy level
Valence Electrons= found in outer most energy level
Na 2-8-1
Cl 2-8-7
Atoms can have a maximum of 8 valence electrons
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Lewis Dot Diagrams
(Electron Dot Diagrams)
Lewis Dot Diagrams
(Electron Dot Diagrams)
• Represent the arrangement of
electrons around the nucleus.
• Electrons are the DOTS.
symbol
• Nucleus is the symbol.
• ONLY REPRESENT VALENCE
ELECTRONS!!
• Fill one side first, then one on each
side before you pair electrons.
Na
B
O
Mg
Cl
Ne
Si
H
N
4