Chapter 4Chapter 4

Arrangement of Electrons in Atoms

Arrangement of Electrons in Atoms

I. The Development of a New Atomic Model

I. The Development of a New Atomic Model

Electromagnetic Radiation:

Electromagnetic Spectrum:

Electromagnetic Radiation:

Electromagnetic Spectrum:

Wavelength (): corresponding points on adjacent waves---Ex:

Frequency (): # of waves that pass a point in a specific time

c = () () ------inversely proportional

Wavelength (): corresponding points on adjacent waves---Ex:

Frequency (): # of waves that pass a point in a specific time

c = () () ------inversely proportional

c = () () ------inversely proportional

c : m/s : m, cm, nm : waves/second--Hertz (Hz)

c = () () ------inversely proportional

c : m/s : m, cm, nm : waves/second--Hertz (Hz)

Photoelectric Effect: emission of e- by certain metals when light shines on them

Photoelectric Effect: emission of e- by certain metals when light shines on them

Quantum: min quantity of nrg that can be lost or gained by an atom

E = (h) ()o J = (Js) (Hz)o Planck’s constant: 6.626 X 10-34 Js

Quantum: min quantity of nrg that can be lost or gained by an atom

E = (h) ()o J = (Js) (Hz)o Planck’s constant: 6.626 X 10-34 Js

• Einsteino dual wave-particle to describe light Photon: radiation with zero mass

carrying a quantum of nrgo packet of nrg emitted when an e- drops

nrg levels

• Einsteino dual wave-particle to describe light Photon: radiation with zero mass

carrying a quantum of nrgo packet of nrg emitted when an e- drops

nrg levels

Ground state: lowest nrg stateExcited state: higher potential nrg

Ground state: lowest nrg stateExcited state: higher potential nrg

--Bohr’s Model----Bohr’s Model--

e- exist only in orbits with specific amounts of energy called energy levels

Therefore…

e- can only gain or lose certain amounts of energy

only certain photons are produced

e- exist only in orbits with specific amounts of energy called energy levels

Therefore…

e- can only gain or lose certain amounts of energy

only certain photons are produced

Line-Emission Spectrum

ground state

excited state

ENERGY IN PHOTON OUT

Bohr Model

1

23

456 -Energy of photon depends on the difference in energy levels-Bohr’s calculated energies matched the IR, visible, and UV lines for the H atom

Other Elements

Each element has a unique bright-line emission spectrum.

“Atomic Fingerprint”

Helium

Bohr’s calculations only worked for hydrogen! ----pg 97

II. The Quantum Model of the Atom

II. The Quantum Model of the Atom

A. Electrons as Waveso Diffraction: bending of a wave as it

passes by the edge of an objecto Interference: results when waves

overlap

A. Electrons as Waveso Diffraction: bending of a wave as it

passes by the edge of an objecto Interference: results when waves

overlap

EVIDENCE: DIFFRACTION PATTERNS

VISIBLE LIGHT ELECTRONS

Heisenberg Uncertainty Principle

Impossible to know both the velocity and

position of an electron at the same time

Schrödinger Wave Equation (1926)finite # of solutions quantized

energy levels

defines probability of finding an e-

Schrödinger Wave Equation (1926)finite # of solutions quantized

energy levels

defines probability of finding an e-

( ) ó3/2 Z∂

11s 0

−= eØ a

A. Atomic Orbitals and Quantum Numbers

A. Atomic Orbitals and Quantum Numbers

Orbital: probable location of an e-Quantum #: properties of atomic

orbitals and properties of e-’s in orbitals

Principal quantum #: (n), indicates main nrg level occupied by the e-o n = 1 -----occupies 1st nrg level

Orbital: probable location of an e-Quantum #: properties of atomic

orbitals and properties of e-’s in orbitals

Principal quantum #: (n), indicates main nrg level occupied by the e-o n = 1 -----occupies 1st nrg level

Angular momentum quantum #: (l), indicates shape of orbital

Magnetic quantum #: (m), orientation of an orbital

Spin quantum #: which spin state (+)(-)

***See table 4-2 pg 104

Angular momentum quantum #: (l), indicates shape of orbital

Magnetic quantum #: (m), orientation of an orbital

Spin quantum #: which spin state (+)(-)

***See table 4-2 pg 104

Orbital (“electron cloud”)

Region in space where there is 90% probability of finding an e-

Orbital Radial Distribution Curve

Four Quantum Numbers:

Specify the “address” of each electron in an atom

UPPER LEVEL

1. Principal Quantum Number ( n )

Energy level

Size of the orbital

n2 = # of orbitals in the energy level

2. Angular Momentum Quantum # ( l )

Energy sublevel

Shape of the orbital

s p

d f

n = # of sublevels per level

n2 = # of orbitals per level

Sublevel sets: 1 s, 3 p, 5 d, 7 f

3. Magnetic Quantum Number ( ml )

Orientation of orbital

Specifies the exact orbitalwithin each sublevel

4. Spin Quantum Number ( ms )

Electron spin +½ or -½

An orbital can hold 2 electrons that spin in

opposite directions.

III. Electron ConfigurationIII. Electron Configuration

Aufbau principle: lowest nrg orbits fill first

Pauli exclusion principle: no 2 e-’s can have the same 4 quantum #’s. This is where spin allows 2 e-’s to be in the same orbito Ex:

Aufbau principle: lowest nrg orbits fill first

Pauli exclusion principle: no 2 e-’s can have the same 4 quantum #’s. This is where spin allows 2 e-’s to be in the same orbito Ex:

Hund’s rule: orbital of equal nrg are occupied by 1 e-, before any is occupied by 2 e-’so Ex:

Orbital Notation: ex: pg 107

Electron Config Notation: pg 107Electron Dot diagram: ex

Hund’s rule: orbital of equal nrg are occupied by 1 e-, before any is occupied by 2 e-’so Ex:

Orbital Notation: ex: pg 107

Electron Config Notation: pg 107Electron Dot diagram: ex

Noble gases:are inertcomplete octet--show ex----

Noble gases:are inertcomplete octet--show ex----

Table 4-3 pg 1101. Principal # energy level2. Ang. Mom. # sublevel (s,p,d,f)3. Magnetic # orbital4. Spin # electron

Table 4-3 pg 1101. Principal # energy level2. Ang. Mom. # sublevel (s,p,d,f)3. Magnetic # orbital4. Spin # electron

Feeling overwhelmed?Feeling overwhelmed?