Unanswered Questions Rutherford’s model did not address the following questions: 1. What is the arrangement of electrons in the atom? 2. What keeps the.

Unanswered Questions

Rutherford’s model did not address the following questions:

1. What is the arrangement of electrons in the atom?

2. What keeps the electrons from converging on the nucleus?

3. What accounts for the differences in chemical behavior among elements?

Bohr Model of the Atom

• Electrons movement around the nucleus is restricted to a particular circular orbit. The “Planetary” model.

• Each orbit is associated with a certain amount of energy• The larger the orbit (farther away from the nucleus) the

greater the energy• In order to move from one orbit to the next, an electron has to

absorb a quantum of energy

• Bohrs model was limited to explaining the behavior of hydrogen

The minimum amount of energy required to move an electron from one level to another

Quantum Mechanical Model• Like Bohr, electrons energies are limited to a certain value• Unlike Bohr, electrons do not travel in prescribed paths.• Electrons travel within a particular volume of space

surrounding the nucleus• The probability of finding an electron in a particular region

of space is represented as a cloud of electrons.

Organization of Electrons in an Atom• Energy Levels (aka principal quantum numbers) n=1,2,3,4,5,6,7

• Energy levels increase as distance from the nucleus increases

• Sublevels (s,p,d,f) • Volume of space defined by a collection of orbitals

• Orbitals• Shapes

Sharp, principal, diffuse, and fundamental

Ground-State Electron ConfigurationArrangement of electron in an atom at restThe lowest energy arrangement is the most stable

Three Rules that govern how electrons can be arranged in an atom:

•Aufbau Principle

Each electron occupies the lowest energy orbital available

•Pauli Exclusion Principle

A maximum of two electrons can occupy a single orbital

•Hund’s Rule

Electrons with the same spin must occupy each orbital before electrons with opposite spins can occupy each orbital

Orbital Filling Sequence

(subshell)(Energy Level)

Benchmark• If you haven’t done so already, you should read pages

127-132 in your textbook. In addition to the material we have covered in class this information should enable you to do the following:

Written work questions on p. 149-152

# 24, 28, 35, 36, 38, 39a, 50p. 153 #2

Orbital Filling Diagram

Electron Configuration

Fluorine (atomic #9)

2 2 5

Orbital Diagram

Nobel Gas Configuration

To shorten the amount of writing required to represent the configuration of elements with large numbers of electrons, the symbol for the noble gas that directly precedes an element can represent all of the electrons up to that point.

1s2 2s2 2p6 3s2 3p6 4s2 [Ar] 4s2

Long Hand Short Hand

Exceptional Electron Configurations

• Not all electron configurations abide by Aufbau’s principle. Half-filled sub-levels are not as stable as filled sublevels, but they are more stable than other configurations.

• Ex. Chromium

According to Aufbau More stable configuration

1s2 2s2 2p6 3s2 3p6 4s23d4

Ground State and Excited State Electron Configurations• The ground state electron configurations represents

electrons in their lowest energy states, following Aufbau’s Principal

Kground: 1s2 2s2 2p6 3s2 3p6 4s1

• In the excited state electrons change position in the atom as they absorb energy, moving to higher energy sublevels or skipping energy levels all together.

Kexcited: 1s2 2s2 2p6 3s2 3p5 4s2

or

Kexcited: 1s2 2s2 2p6 3s2 3p6 4p1

Benchmark• If you haven’t done so already, you should read pages

133-136 in your textbook. In addition to the material we have covered in class this information should enable you to do the following:

Written work questions on p. 149-152 # 64, 68, 71

p. 153 # 6,8,10

Chemical Behavior Related to the Arrangement of Electrons

In the early 1900’s scientist observed that when they heated elements in a flame, the elements emitted colored light. Analysis of the light led scientist to determine that the arrangement of electrons in an atom is related to the elements chemical behavior.

Understanding Light – Characteristics of Waves

CA

1 sec

D

E

Using the word bank below, match the words to the lettered parts of the diagram

B = 3/s

Frequency Amplitude Peak Trough Wavelength

Waves CharacteristicsWavelength () the shortest distance between two equivalent points on a wave.

(unit of measure: meters, centimeters, or nanometers)

Frequency (v) the number of waves that pass a given point per second.

(unit of measure: Hz, waves/second, /s, s-1)

c v

Waves

c=v

Speed of Light (c) = 3.0 x 108m/s

Relationship Between Wavelength and Frequency c=v

Fre

que

ncy

Wavelength

Electromagnetic SpectrumElectromagnetic radiation – Form of energy that exhibits wave-like behavior.

Electromagnetic spectrum – encompasses all forms of electromagnetic radiation. The only differences between each form is their characteristic wavelengths and frequencies.

White Light – a continuous spectrum of colors, each with a unique wavelength and frequency.

The Electromagnetic SpectrumWhich of the following waves has the longest wavelength? Which has the greatest frequency?

Line Spectra

Einstein’s Contribution

Ephoton=hv

Explained that electromagnetic radiation behaves both like waves and particles.

Photon – a particle of electromagnetic radiation with no mass that carries a quantum of energy.

Equantum=hv

E = energy

h = Planck’s constant=6.626 x 10-34J

V = frequency

Relationships between wavelength, frequency and Energy

Fre

que

ncy

Wavelength

En

erg

y

FrequencyE

ner

gy

Wavelength

Electrons as Waves (Louis de Broglie)

•de Broglie proposed the idea that all particles have wavelengths

•Wavelengths of large bodies are too small to observe and therefore principals of classical physics best describes their movement

•Quantum mechanics provides a more suitable explanation of the movement of subatomic particles

mv

h

Photoelectric Effect

Electrons are emitted from a metal’s surface when light of a certain minimum frequency of 1.14 x 1015 Hz shines on the surface.

(Conversion of light energy to electrical energy)

Heisenberg Uncertainty Principle

• Premise: It is impossible to make any measurement on an object without disturbing the object.

The position of electron can be determined by shooting photons at electrons in an atom

• It is impossible to know precisely both the velocity and position of a particle at the same time

Benchmark• If you haven’t done so already, you should read pages

138-146 in your textbook. In addition to the material we have covered in class this information should enable you to do the following:

Written work questions on p. 149-152 # 45, 55, 61, 63, 75, 83, 92, 94

p. 153 # 4, 12