Transcript Electron Arrangement

Electron Arrangement
Subatomic Particles
• All atoms consist of the same three subatomic
particles: protons, neutrons, and electrons.
• Only the number of each varies from element to
element.
• Atoms are neutral, so the number of protons
(positively charged) must be equal to the number of
electrons (negatively charged).
• Based on Rutherford’s Gold Foil Experiment, it was
determined that the protons are located in the
nucleus and the electrons are moving about the
nucleus.
Planetary Model
• According to the planetary model, electrons
orbit the nucleus much like planets orbit the
sun.
• The different “orbits” the electrons occupy are
referred to as energy levels.
• The lowest energy level is the orbit closest to
the nucleus.
Energy Levels
• The lowest energy level (energy level 1) can hold a
maximum of 2 electrons.
• Energy level 2 can hold a maximum of 8 electrons. Energy
level 2 is farther from the nucleus than energy level 1 and is
therefore larger in size.
• Energy level 3 can hold a maximum 18 electrons.
• The equation 2n2 can be used to determine the maximum
number of electrons in any energy level. (n is the energy
level number)
• Note: There is never more than 8 electrons in the outer
level. (We will learn why in the next unit)
• Electrons found in the outer level are called valence
electrons.
Bohr Diagrams
• A Bohr Diagram is a method for representing
the arrangement of electrons within an atom.
Atomic Number
• Moseley, in an experiment called the X-ray
tube experiment, determined that each
element has a different and unique number of
protons.
• The number of protons is referred to as the
element’s atomic number.
• The atomic number can be used to identify
the element.
• Atomic Number = # of protons= # of electrons.
Mass Number
• The mass number is the total number of
particles located in the nucleus.
• Mass Number = # of protons + # of neutrons
• To determine the number of neutrons,
subtract the atomic number from the mass
number.
• Mass # - atomic # = # of neutrons
Nuclear Symbol
• A nuclear symbol can be used to represent the
number of subatomic particles found in an
atom.
• Example:
35
17
Mass Number
Cl
Atomic Number
How many protons, neutrons, and
electrons are found in this atom?
Bohr Diagram
• Draw the Bohr diagram for the atom of
chlorine.
17 p
18 n
More Bohr Diagrams
• Draw the Bohr diagrams for the elements
represented by the following nuclear symbols:
Isotopes
• In an experiment working with neon atoms,
Thomson discovered some of the atoms had
different masses.
• Because they all were neon, the number of
protons and electrons were all the same.
• Therefore, the difference in mass was due to
different numbers of neutrons.
• He called these different atoms isotopes.
• This discovery led to a revision of what part of
Dalton’s theory?
Examples of Isotopes
Determine the number of protons,
electrons, and neutrons for each of
the isotopes of carbon.
The atomic number identifies the
element. The mass number
identifies the isotope. Therefore,
when identifying an isotope by
name, the mass number is shown.
Example: carbon-12