chapter 7: completing the model of the atom section 7.1: expanding the theory of the atom
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Chapter 7: Completing the Model of the Atom
Section 7.1: Expanding the Theory of the Atom
Electrons Occupy a complex world of energy
levels electron distribution in energy levels of
an atom account for many of the physical and chemical properties of the element
Energy levelsElectrons with the most energy are
farthest from the nucleus and occupy the outermost level
Review of Electromagnetic Radiation and Energy levels Waves have a range of freq. and
wavelengths Higher freq = Shorter wavelength =
Greater energy Lower freq = Longer wavelength = Lower
energy
Review of Electromagnetic Radiation and Energy levels (cont)• Use to calculate the exact amount of energy released by
electrons in atoms
• By absorbing a specific amount of energy, an e- can jump to a higher energy level
• When an e- falls back to a lower energy level, it releases the
same amount of energy in the form of radiation (light) with a definite frequency
• The energy (color) of light depends on how far the electron falls
• Greater energy = Color more toward the violet end of spectrum
Heisenberg’s Uncertainty Principle States that it is impossible to measure
exactly both the position and momentum (mass and speed) of an object (electron)
This led to the electron cloud model in atoms
Electron cloud modelBecause we cannot pinpoint exactly
where an electron is on the “surface” of an atom, we refer to its position as an electron cloud.
The chemical behavior and properties of any 2-subtances are determined by the number of these electrons around the nucleus
How do we describe the electron cloud? We use quantum numbers. These
represent the energy states of the electron.
These difference in energy states were “discovered” due to the different spectral lines of an emission spectrum.
Quantum NumbersThere are 4 quantum numbers that
describe the electron distribution of electrons in an atom
They are n, l, m and s
Principal quantum number, n
• Describes the general size of the electron cloud• Numbered levels low to high – 1,2,3,4…(integers)• Electrons may be found in each• The maximum # of electron possible in any one
level is 2n2 • We have been calling these energy levels, 1-7• Each main energy level has sublevels
Angular quantum number, l Describes the shape of the electron
cloud It represents the sublevels within an
energy level The value of l is 0 to (n-1) The number of sublevels is equal to the
value of n The lowest sublevel is s, then p, d and f
Angular quantum number, l (cont) Each sublevel can hold up to a specific
# of electrons: s sublevel can hold 1 pair (2 electrons) p can hold 3 pair (6 electrons) d can hold 5 pair (10 electrons) f can hold 7 pair (14 electrons)
Each pair has a different place in space, this space is called an orbital.
Orbitals
Angular quantum number, l (cont) The sum of all the electron clouds in any
sublevel is a spherical cloud. Electrons are repelled by each other and
attracted to the positive nucleus
Blocks in the Periodic Table
Magnetic Quantum Number, m Describes the orientation in space of a
particular orbital The value is any integer between +l and
-l
Electron Spin Quantum Number, s Describes the spin of the electron within
an orbital The value is +1/2 (clockwise) or -1/2
(counterclockwise) If there are 2 electrons in an orbital,
they must spin in opposite directions.
Hund’s RuleIn a set of orbitals, the electrons will fill the orbitals
in a way that would give the maximum number of parallel spins (maximum number of unpaired electrons).
Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.
Orbital Diagram for Hydrogen
OrbitalDiagram for Helium
Orbital Diagram for Lithium
Orbital Diagram for Beryllium
OrbitalDiagram for Carbon
Orbital Diagram for Nitrogen
Standard Notation of Fluorine
Main Energy
Level
Numbers
1, 2, 2Sublevels
Number of electrons in the sub level 2,2,5
1s2 2s2 2p5
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