Electron Structure of the Atom

Chapter 7

7.1 Electromagnetic Radiation and Energy

Electromagnetic Radiation

• EM Radiation travels through space as an oscillating waveform.

• EM Radiation travels through a vacuum at a constant speed of 3.00×108 m/s

Properties of EM Radiation

• Wavelength (λ, measured in nm)• Frequency (υ, measured in Hertz, Hz)

Relationship between λ and υ

Electromagnetic Spectrum

Mathematical Relationships

υλ = cυ = Frequency of the light (1/s, or Hz)λ = Wavelength of light (nm or m)c = CONSTANT, Speed of light (3.00×108 m/s)

Mathematical Relationships

Ephoton=hυ Ephoton=(hc)/λυ = Frequency of the light (1/s, or Hz)λ = Wavelength of light (nm or m)c = CONSTANT, Speed of light (3.00×108 m/s)h = Planck’s Constant (6.626×10-34 J×s)Ephoton = Energy of a single photon (J)

Example

• Assume we want to determine the frequency of orange light and the energy of a single photon of this light.

• Orange light = 600 nm = 6.00×10-7 m• υλ = c, therefore υ = c/λ• = 5.00×1014 Hz• Ephoton=hυ=(6.626×10-34 J×s)(5.00×1014

Hz)• Ephoton=3.31×10-19 J

PROBLEM

• Calculate the frequency and photon energy for an X-ray of wavelength 1.00 nm.

• X-Ray= 1.00 nm = 1.00×10-9 m• υλ = c, therefore υ = c/λ• = 3.00×1017 Hz• Ephoton=hυ=(6.626×10-34 J×s)(3.00×1017

Hz)• Ephoton=1.99×10-16 J

PROBLEM

• What color is laser with a frequency of 6.0×1014 Hz?

• therefore • = 5.00×10-7 m = 500 nm• 500 nm = Green Light

Continuous vs. Line Spectra

7.2 The Bohr Model of the Hydrogen Atom

Bohr Model of the Atom

• Propsed by Niels Bohr• Explains the Emission

Spectrum of Hydrogen• Relies of quantitized

energy levels.• Does not work for

atoms with more than one electron.

7.3 The Modern Model of the Atom

Orbitals and Orbits

• Bohr’s model had electrons orbit in tight paths, but this only worked for Hydrogen.

• Schrödinger expanded the model by using 3 dimensional orbitals

Energy Levels and Orbital Shape

• Electrons are still in quantitized energy levels.

• Orbitals of roughly the same size are in the same overarching, or principal, energy level.

• There are four ground state orbital geometries: s, p, d and f.

Naming Orbitals

• Orbitals are named for their principal energy level and their orbital geometry.

• The n=1 principal energy level has only one geometry, s.

• The n=2 principal energy level has two geometries, s and p.

• n=3 is composed of s, p, and d• n=4 is composed of s, p, d and f.

Orbital Geometries

Orbital Diagrams

Rules for Filling in Orbitals

• Ground State Atoms have the same number of electrons as protons.

• Aufbau Principle – Start with the lowest energy level.

• Pauli Exclusion Principle – Max of two electrons in each orbital with opposite spins

• Hund’s Rule – Electrons are distributed in orbitals of the same energy as to maximize the number of unpaired electrons.

Example

Sodiump= 11e= 11

PROBLEM

Carbon

PROBLEM

Titanium

Electron Configurations

• Orbital diagrams are informative but take a lot of space.

• Electron Configurations are a shorthand for these diagrams.

• Though they convey the same information, they do not show sublevel organization.

Example

Sodiump= 11e= 11

Na 1s2 2s2 2p6 3s1

PROBLEM

Nitrogen

PROBLEM

Iron

7.4 Periodicity of Electron Configuration

Periodic Table

Another Way to Look at It

7.5 Valance Electrons in the Main Group Elements

Main Group Elements

Valance Electrons

• Valance Electrons are those electrons in the last filled principal energy level.

• Core Electrons are those below the valance level.

• Valance Electrons for Main Group Elements are those in the highest s and p orbitals.

• Main Elements in the same group have the same number of valance electrons.

7.6 Electron Configurations for Ions

Example

Sodium ionp= 11e= 10

Na 1s2 2s2 2p6

Ion Electron Configurations

• Ion charges are as they are due to the role of orbitals.

• Ions are stable at 1+, 2+, or such because that gets the electron configuration to a completed principal energy shell (for main group elements).

• Na (1+) is isoelectronic with Neon (a completed n=2)

7.7 Periodic Properties of Atoms

Valance Electrons and Chemistry

• Valance electrons are the ones participating in chemical reactions.

• Compounds are stabilized by reaching a filled principal energy level.

• We will return to this next chapter.

Ionization Energy

• Ionization Energy, the amount of energy required to remove en electron from an gaseous atom (kJ/mol)

• The lower the ionization energy the more reactive a compound is.