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Ledermann
Chemistry Unit 4
Chapter 4 Learning Targets: Arrangement of electrons and atoms
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Describe and diagram the Bohr model.
Compare and contrast Bohr’s model and the Quantum model.
Describe the significance of the four quantum numbers.
Relate the number of sublevels corresponding to each of an atom’s main energy levels.
Relate the number of orbital’s corresponding to each of an atom’s sublevels.
Identify the number of orbitals per energy level.
Determine the total number of electrons to fill an energy level.
State the Aufbau principle, the Pauli Exclusion Principle and Hund’s rule.
Write an electron configuration.
I
Niels _Bohr developed a model of the atom based on the experimental emission-line
spectrum of _hydrogen_
A. Bohr observed atoms are in either _ground state or an _excited state and that the emission-line
spectrum is not continuous.
1 Bohr proposed that electrons can only “_orbit_” the nucleus in allowed regions.
a. Electrons in the lowest or ground_ state are closest to the nucleus.
b. When they _gain energy they “jump” out to a higher “energy level”
This is called _excited_state. (unstable)
c. When electrons “ fall” back down to their original location they emit a specific
or_quantized amount of energy. This is observed as spectral emission-lines.
d. Draw a Bohr model of Mg:
I.
The _Electron Cloud _ Model of the Atom.
a. Louis de Broglie said electrons act like light, both as a particle and a wave
b. The Quantum Theory mathematically describes the wave properties of electrons
1. An orbital is a three-dimensional region around the nucleus based on the
probability of the location of an electron. These can be a variety of shapes
c. Quantum numbers identify the properties of atomic orbitals and the electrons in the the
orbitals. They can uniquely describe each element.
i. The energy_ level is described as the principle quantum number.
1. These increase from _1_and go up. (Typically 1-7 )
2. They indicate how _far_ away an electron is from the nucleus. The higher
the number the further away.
ii. The _sublevels__are referred to as the angular momentum.
1. These indicate the shapes of the orbitals
2. Each orbital can only hold a maximum of _2_electrons
3. Each type of orbital has a specific type of shape
a. s is __spherical_
b. p is like two _figure 8’s (dumbells)_ connected at the ends. These
can be oriented three different ways.
iii. The x,y,z orientation is the magnetic quantum number.
1. For the s orbitals there can only be one possibility 0
2. p orbitals have 3 possibilities x, y, or z numbered -1, 0,1
iv.
The Spin indicates the direction of spin for the electron.
1. Each orbital can only hold 2_electrons and each must have an
_opposite__spin.
Brief summary table:
Energy Level
1
2
3
4
Sublevels
s
s,p
s,p,d
s,p,d,f
Orbitals
1s
1 s and 3 p’s
1s, 3 p’s and 5 d’s
1s 3 p’s 5 d’s 7 f’s
Number of e2
8
18
32
How many electrons can the 2nd energy level hold?
There are 2 sublevels, s and p. There is one s orbital and 3 p orbitals. Each
Orbital can hold 2 electrons, so there will be 8 electrons in the 2nd energy level.
Rules:
1. Aufbau__principle (build up)
Electrons enter the lowest energy levels available first. S then p then d then f
2. _Pauli Exclusion__ principle
Any atomic orbital can hold a maximum of 2 electrons. The electrons must have
opposite spins (opposites attract).
3. Hund’s_Rule
Electrons won’t pair up until each orbital of that sublevel has one electron
Orbital: a region in space where the probability of finding an electron is high. (It is a place in the atom
where you are most likely to find an electron. )
There are 4 possible sublevels:
s has 1 orbital (2 electrons)
p has 3 orbitals (6 electrons)
d has 5 orbitals (10 electrons)
f has 7 orbitals (14 electrons)
There are always n2 orbitals per energy level and 2 electrons per orbital ( n = the energy level). There is
a maximum of 2n2 per energy level. Example: Energy level has a maximum of 2(3)2 or 18 electrons.
Electron configurations
are a list of the way electrons are arranged around the nucleus. Ex: Oxygen 1s 22s22p4
Examples: Identify the element with the configuration 1s22s22p63s23p3______________________
Write the electron configuration for Boron (B).
Write the arrow notation for oxygen.