New Way Chemistry for Hong Kong A-Level Book 11 Chapter 4 The Electronic Structure of Atoms 4.1The...
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Transcript of New Way Chemistry for Hong Kong A-Level Book 11 Chapter 4 The Electronic Structure of Atoms 4.1The...
New Way Chemistry for Hong Kong A-Level Book 11
Chapter 4Chapter 4The Electronic Structure of AtomsThe Electronic Structure of Atoms
4.14.1 The Electromagnetic SpectrumThe Electromagnetic Spectrum
4.24.2 Deduction of Electronic Structure Deduction of Electronic Structure from Ionization Enthalpies from Ionization Enthalpies
4.34.3 The Wave-mechanical Model of The Wave-mechanical Model of the Atom the Atom
4.44.4 Atomic Orbitals Atomic Orbitals
New Way Chemistry for Hong Kong A-Level Book 12
The Electronic Structure of Atoms
Niels Bohr
Bohr’s Model of H atom
Chapter 4 The electronic structure of atoms (SB p.90)
New Way Chemistry for Hong Kong A-Level Book 13
The Electronic Structure of Atoms
Niels Bohr
Bohr’s Model of H atom
Chapter 4 The electronic structure of atoms (SB p.90)
New Way Chemistry for Hong Kong A-Level Book 14
The Electromagnetic Spectrum
c
4.1 The Electromagnetic Spectrum (SB p.91)
c
New Way Chemistry for Hong Kong A-Level Book 15
Continuous spectrum of white light
Fig.4-5(a)
4.1 The Electromagnetic Spectrum (SB p.92)
New Way Chemistry for Hong Kong A-Level Book 16
Line Spectrum of hydrogen4.1 The Electromagnetic Spectrum (SB p.93)
Fig.4-5(b)
New Way Chemistry for Hong Kong A-Level Book 17
The Emission Spectrum of Atomic Hydrogen
UV Visible IR
4.1 The Electromagnetic Spectrum (SB p.93)
New Way Chemistry for Hong Kong A-Level Book 18
Interpretation of the Atomic Hydrogen Spectrum
4.1 The Electromagnetic Spectrum (SB p.94)
New Way Chemistry for Hong Kong A-Level Book 19
Interpretation of the Atomic Hydrogen Spectrum4.1 The Electromagnetic Spectrum (SB p.94)
New Way Chemistry for Hong Kong A-Level Book 110
Interpretation of the Atomic Hydrogen Spectrum4.1 The Electromagnetic Spectrum (SB p.94)
New Way Chemistry for Hong Kong A-Level Book 111
Bohr proposed for a hydrogen atom:
1. An electron in an atom can only exist in certain states characterized by definite energy levels (called quantum).2. Different orbits have different energy levels. An orbit with higher energy is further away from the nucleus.3.When an electron jumps from a higher energy level
(of energy E1) to a lower energy level (of energy E2), the energy emitted is related to the frequency of light recorded in the emission spectrum by:
E = E1 - E2 = h
4.1 The Electromagnetic Spectrum (SB p.95)
New Way Chemistry for Hong Kong A-Level Book 112
4.1 The Electromagnetic Spectrum (SB p.96)
How can we know the energy levels are getting closer and closer together?
New Way Chemistry for Hong Kong A-Level Book 113
4.1 The Electromagnetic Spectrum (SB p.97)
E = E1 - E2 = h
Planck ’s constant
Frequency of light emitted
New Way Chemistry for Hong Kong A-Level Book 114
Emission spectrum of hydrogen
Absorption spectrum of hydrogen
dark background(photographic plate)
bright lines
bright background(photographic plate)
dark lines
4.1 The Electromagnetic Spectrum (SB p.97)
New Way Chemistry for Hong Kong A-Level Book 115
Production of the Absorption Spectrum
Absorption spectrum of hydrogen
4.1 The Electromagnetic Spectrum (SB p.97)
bright background(photographic plate)
dark lines
New Way Chemistry for Hong Kong A-Level Book 116
Convergence Limits and Ionization
What line in the H spectrum corresponds to this electron transition (n= ∞ n=1)?
What line in the H spectrum corresponds to this electron transition (n= ∞ n=1)?
Last line in the Lyman SeriesLast line in the Lyman Series
For n=∞ n=1:
4.1 The Electromagnetic Spectrum (SB p.97)
H (g) H+(g) + e-
New Way Chemistry for Hong Kong A-Level Book 117
The Uniqueness of Atomic Emission Spectra
No two elements have identical atomic spectraatomic spectra can be used to identify unknown elements.
4.1 The Electromagnetic Spectrum (SB p.99)
New Way Chemistry for Hong Kong A-Level Book 118
Ionization Enthalpy
Ionization enthalpy (ionization energy) of an atom is the energy required to remove one mole of electrons from one mole of its gaseous atoms to form one mole of gaseous positive ions.
Ionization enthalpy (ionization energy) of an atom is the energy required to remove one mole of electrons from one mole of its gaseous atoms to form one mole of gaseous positive ions.
The first ionization enthalpy
M(g) M+(g) + e- H = 1st I.E.
The second ionization enthalpy
M+(g) M2+(g) + e- H = 2nd I.E.
4.2 Deduction of Electronic Structure from Ionization Enthalpies (p.100)
New Way Chemistry for Hong Kong A-Level Book 119
Evidence of Shells
shells
4.2 Deduction of Electronic Structure from Ionization Enthalpies (p.101)
New Way Chemistry for Hong Kong A-Level Book 120
Evidence of Sub-shells
4.2 Deduction of Electronic Structure from Ionization Enthalpies (p.102)
2,1
2,2
2,3
2,4
2,5
2,6
2,7
2,8 subshells
New Way Chemistry for Hong Kong A-Level Book 121
Bohr’s Atomic Model and its LimitationsBohr considered the electron in the H atom (a one-electron system) moves around the nucleus in circular orbits.
Basing on classical mechanics, Bohr calculated values of frequencies of light emitted for electron transitions between such ‘orbits’.
The calculated values for the frequencies of light matched with the data in the emission spectrum of H.
4.3 The Wave-mechanical Model of the Atom (p.104)
New Way Chemistry for Hong Kong A-Level Book 122
Bohr’s Atomic Model and its Limitations
Bohr tried to apply similar models to atoms of other elements (many-electron system), e.g. Na atom.
Basing on classical mechanics, Bohr calculated values of frequencies of light emitted for electron transitions between such ‘orbits’.
The calculated values for the frequencies of light did NOT match with the data in the emission spectra of the elements.
The electron orbits in atoms may NOT be simple circular path.
4.3 The Wave-mechanical Model of the Atom (p.104)
New Way Chemistry for Hong Kong A-Level Book 123
Wave Nature of Electrons
A beam of electrons shows diffraction phenomenonElectrons possess wave properties
(as well as particle properties).
4.3 The Wave-mechanical Model of the Atom (p.104)
New Way Chemistry for Hong Kong A-Level Book 124
Wave Nature of ElectronsSchrödinger used complex differential equations/wave fucntions to describe the wave nature of the electrons inside atoms (wave mechanic model).
The solutions to the differential equations describes the orbitals of the electrons inside the concerned atom.
An orbital is a region of space having a high probability of finding the electron.
4.3 The Wave-mechanical Model of the Atom (p.104)
New Way Chemistry for Hong Kong A-Level Book 125
Quantum NumbersElectrons in orbitals are specified with a set of numbers called Quantum Numbers:
1. Principal quantum number (n) n = 1, 2, 3, 4, …...
2. Subsidiary quantum number (l) l = 0, 1, 2, 3…, n-1 s p d f
3. Magnetic quantum number (m) m = -l, …, 0, …l
4. Spin quantum number (s) s= +½, -½
The solutions of the wave functions are the orbitals -- which are themselves equations describing the electrons.
The solutions of the wave functions are the orbitals -- which are themselves equations describing the electrons.
4.3 The Wave-mechanical Model of the Atom (p.104)
New Way Chemistry for Hong Kong A-Level Book 126
4.3 The Wave-mechanical Model of the Atom (p.105)
Principal quantum number
(n)
Subsidiary quantum
number (l)
Number of orbitals (2l+1)
Symbol of orbitals
Maximum number of electrons
held1 0 1 1s 2
2 01
13
2s2p
26
3 012
135
3s3p3d
56
104 0
123
1357
4s4p4d4f
26
1014
8
18
32
New Way Chemistry for Hong Kong A-Level Book 127
Each orbital can accommodate 2 electrons with opposite spin.
1s
2s
2p
3s
3p
3d
4s
4.3 The Wave-mechanical Model of the Atom (p.105)
New Way Chemistry for Hong Kong A-Level Book 128
The s Orbitals
4.4 Atomic Orbitals (p. 107)
New Way Chemistry for Hong Kong A-Level Book 129
The s Orbitals4.4 Atomic Orbitals (p.107)
New Way Chemistry for Hong Kong A-Level Book 130
The p Orbitals
4.4 Atomic Orbitals (p.109)
New Way Chemistry for Hong Kong A-Level Book 131
The END