Arrangement of Electrons in Atoms

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• CHAPTER 4
• Section 1
• Arrangement of Electrons in Atoms

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• In Rutherfords model of the atom one of the
  major problems was that it did not explain how
  negative electrons fill the space surrounding the
  nucleus.
• Visible light is a kind of electromagnetic
  radiation, which is a form of energy that
  exhibits wavelike behavior as it travels through
  space.

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• The electromagnetic spectrum is all of the forms
  of electromagnetic radiation.
• Visible light is only a small part of the
  electromagnetic spectrum. Its wavelength is from
  400 nm to 700 nm.
• The frequency and wavelength are mathematically
  related to each other.

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• In the equation c is the speed of light which is
  equal to 3 x 10 8 m/s
• Wavelength ( ) is the distance between
  corresponding points on adjacent waves.
• Frequency is (v) and is defined as the number of
  waves that pass a given point in a specific time.
  
• Frequency is measured in waves/second. One
  wave/second is called a hertz (Hz).

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• EX Determine the frequency of light with a
  wavelength of 4.257 x 10-9 m.

Rearrange to
3.0 x 10 8 m/s
7.0 x 10 16 Hz
4.257 x 10 -9 m
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• The photoelectric effect refers to the emission
  of electrons from a metal when light shines on
  the metal. Which creates an electric current.
• Light as particles
• German physicist, Max Planck, was studying the
• emission of light by hot objects.
• Planck suggested that the objects emit energy in
  small specific amounts called quanta. A quantum
  is the minimum quantity of energy that can be
  lost or gained by an atom.

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• Planck produced the following relationship
• E(h) (v)
• E to the energy in joules, of a quantum of
  radiation.
• v to the frequency of the radiation emitted
• h is the fundamental physical constant now known
  as Plancks constant
• h 6.626 x 10-34 js

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• A photon is a particle of electromagnetic
  radiation having a zero rest mass and carrying a
  quantum of energy.
• The dual wave-particle nature of light depends on
  the experiment that observes it, light behaves
  like a wave or like a particle.
• When a current is passed through a gas at a low
  pressure, the potential energy of some of the gas
  atoms increases. The lowest energy state of an
  atom is its ground state. A state in which an
  atom has a higher potential energy than it has in
  its ground state is called an excited state.

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• The Bohr model of the hydrogen atom depicts a
  hydrogen nucleus with a single electron circling
  the nucleus at a specific radius called an orbit.
  The electron exists in only one of only a finite
  number of allowed orbits.

E
1 p
0 n
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• Section 4.2
• The main energy level is the level of increasing
  energy, specified by the quantum number n, at
  which atomic orbitals can exist.
• Quantum numbers specify the properties of atomic
  orbitals and the properties of electrons in
  orbitals.
• The principal quantum number is the number used
  to specify the main energy level of an atom.
• The principal quantum number is symbolized by n.
  The values of n are positive integers only
  1,2,3, and so on.

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• The electron shells are all of the orbitals
  within the same main energy level.
• The total number of orbitals per main energy
  level is equal to n2. The number of electrons
  allowed per main energy level is equal to 2n2.
• The angular momentum quantum number indicates an
  orbitals shape. And is symbolized by l.
• A sublevel or subshell, consists of the orbitals
  within a given main energy level that share the
  same value of l.
• The magnetic quantum number, symbolized by m,
  indicates the orientation of an orbital around
  the nucleus.

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• The Spin Quantum number has only two possible
  values ( ½, - ½ ) which indicates the two
  fundamental spin states of an electron in an
  orbital.

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• Section 4.3
• The arrangement of electrons in an atom is known
  as the atoms electron configuration.
• Rules for Electron Configuration
• Aufbau Principle is an electron occupies the
  lowest energy orbital that can receive it.
• Pauli exclusion principle is that no two
  electrons in the same atom can have the same set
  of four quantum numbers.

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• Hunds Rule is that 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 spins
• Orbital Notation
• Unoccupied orbital is represented by a line ____
• 1s
• An orbital containing one electron is represented
  as __?__
• 1s
• An orbital containing two electrons is
  represented as ??
• 1s
• Showing the electrons paired with opposite spins.
• Ex H ? He ??
• 1s
  1s

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• The hydrogen configuration is represented by 1s1.
  The superscript indicates that one electron is
  present in hydrogens 1s orbital.
• The helium configuration is represented by 1s2.
  Here the superscript indicates that there are two
  electrons in heliums 1s orbital.
• The three methods used to represent the
  arrangement of electrons are the
• orbital notation
• electron-configuration notation
• noble-gas notation.

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The three methods used to represent the
arrangement of electrons are
A) orbital notation
B) electron-configuration notation
C) noble-gas notation
?
?
?
?
?
?
__
__
__
__
__
__
Na
?
?
?
?
?
1
s
2
s
2
p
Ne
2
2
3
s
3
s
6
1
1
3s
1s
2s
2px
2py
2pz
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• An octet of electrons corresponds to filled s and
  p orbitals in an atoms highest main energy
  level. Noble gas (except helium) contain octets.

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n 5
Increasing energy
5p
4d
5s
4p
3d
4s
3p
3s
2p
n 2
2s
n 1
1s
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