CHEM 111 UNIT 02 - Atomic Structure & Periodicity
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Transcript of CHEM 111 UNIT 02 - Atomic Structure & Periodicity
ATOMIC STRUCTURE AND PERIODICITYUNIT 2
Atomic Structure
THE QUANTUM MECHANICAL MODEL OF ATOMUNIT 2
Quantum Mechanical Model of an Atom
De Broigle’s Matter-waveElectron bound to an atom
behave both as a particle and a wave.
Quantum Mechanical Model of an Atom
Heisenberg Uncertainty Principle It is impossible for us to know
simultaneously the exact momentum and the exact position of a particle in space.
The more precisely the position of the particle is measured or determined, the less precisely its momentum can be known, and vice versa.
Quantum Mechanical Model of an Atom
Schrodinger’s Equation
Ψ – wave function (orbital) Ψ2 – probability distribution
of the electron
𝑯𝝋=𝑬𝝋
Quantum Mechanical Model of an Atom
So how are the electrons moving around a nucleus?
We don’t exactly know.We can only determine the
probability of finding the electron at an area.
QUANTUM NUMBERSUNIT 2
Quantum Numbers
Ψ – orbital that satisfies the Schrodinger’s Equation
Ψ2 – probability distribution
Quantum NumbersNumbers that characterizes the orbitals
Quantum Numbers
Principal Quantum Number (n)can have positive integers
Azimuthal Quantum Number (l)can have integral values from 0 to
(n-1)Magnetic Quantum Number (ml)
can have integral values from –l to l
Quantum Numbers
Principal Quantum Number (n)
Relates the sizeand energy of theorbitalAs n increases
the orbital gets larger the electron spends more time farther than the
nucleus The energy increases
Quantum Numbers
Azimuthal Quantum Number (l) related to the shape of the orbital
Quantum Numbers
Magnetic Quantum Number (ml) related to the orientation of the orbital in
space
Quantum Numbers
s-orbital
Quantum Numbers
p-orbital
Quantum Numbers
d-orbital
Quantum Numbers
f-orbital
Quantum Number
ELECTRON SPINUNIT 2
Electron Spin Number
4th quantum number (ms)
Related to the magnetic properties of the atom
Can be ½ (up spin) or - ½ (down spin)
Pauli’s Exclusion Principle
No two electrons can have the same set of quantum numbers (n, l, ml, ms)
Each orbital can have a maximum of two electrons, one up-spin, and another down spin
Quantum Numbers
Example. Quantum NumbersDetermine which of the following sets of quantum number are not allowed?n = 3, l = 2, ml = 2, ms = ½
n = 4, l = 3, ml = 4, ms = ½
n = 0, l = 0, ml = 0, ms = -½n = 2, l = -1, ml = 1, ms = -½
Quantum Numbers
Example Quantum NumbersGive the maximum number of electrons in an atom for the following quantum numbers.n = 4n = 5, ml = 1
n = 5, ms = ½n = 3, l = 2
ELECTRON CONFIGURATIONUNIT 2
Electron Configuration
describes how electrons are distributed among the various orbitals of an atom
Aufbau’s PrincipleThe orbitals are filled in order of increasing
energy
Electron Configuration
1s 2Energy Level (Principal Quantum #) Sub Level
(s, p, d, f )
# of e- in sub level
Electron Configuration
Orbitals that have lower n have lower energy
Orbitals that have lower l have lower energy s < p < d < f
Electron Configuration
Electron Configuration
Element Orbital Diagram Electron Configuration
Li(3 e-)
B(5 e-)
2s 2px
2py 2pz
1s
2s 2px
2py 2pz
1s
1s2 2s1
1s2 2s2
2p1
Electron Configuration
Hund’s Rule for degenerate orbitals (orbitals having the
same energy), the lowest energy is attained when the number of electrons having the same spin is maximized
Electron Configuration
Element Orbital Diagram Electron Configuration
C(6 e-) 1s2 2s22p2
2O(8 e-) 1s2 2s2 2p5
2s 2px
2py 2pz
1s
2s 2px
2py 2pz
1s
Electron Configuration
Electron Configuration
Condensed Electron ConfigurationMg – 1s2 2s2 2p6 3s2
Mg – [Ne] 3s2
Elements in the same group (vertical column) have the same valence electron configurations
core e-
valence e-
Electron Configuration
Element Condensed Electron Configuration
O(8 e-) [He] 2s2 2p4
Si(14 e-) [Ne] 3s2 3p2
K(19 e-) [Ar] 4s1
Electron Configuration
Transitional Metals
Element Condensed Electron Configuration
V [Ar] 4s2 3d3
Hg [Xe] 6s2 4f10 5d10
Electron Configuration
Example. Electron ConfigurationGive the expanded and the condensed electron configuration and draw the condensed orbital diagram for the following elements.SulfurCadmiumHafmium
PERIODIC TABLEUNIT 2
Periodic Table of Elements
PERIODIC TRENDSUNIT 2
Atomic Radius
Atomic Radius
Left to Rightas p+ and e-
increases, the attraction of the nucleus and valence e- increases
Up to Downas n increases, energy
level increases, its distance from nucleus increases
Ionic Radius
Ionization Energy
Minimum energy required to remove an electron from the ground state of the isolated gaseous atoms
X(g) X+(g) + e-
The higher the IE, the harder it is to remove an electron
Ionization Energy
Electron Affinity
Energy associated with the addition of an electron to an atom in gaseous state
X(g) + e- X-(g)
Measures the ease of an atom to accept an electron
Electron Affinity
Electronegativity
Measure of a tendency of atom to attract a bonding pair
Electronegativity