Chem chapt 5

Electrons in AtomsElectrons in Atoms

Light, a form of electronic radiation, Light, a form of electronic radiation, has characteristics of both a wave and has characteristics of both a wave and a particlea particle

Wavelike properties of electrons help Wavelike properties of electrons help relate atomic emission spectra, energy relate atomic emission spectra, energy states of atoms, and atomic orbitals.states of atoms, and atomic orbitals.

A set of three rules determines the A set of three rules determines the arrangement in an atom.arrangement in an atom.

Main IdeasMain Ideas

Light and Quantized Light and Quantized EnergyEnergy

• Compare the wave and particle natures of light.

• Define a quantum of energy, and explain how it is related to an energy change of matter.

• Contrast continuous electromagnetic spectra and atomic emission spectra.

Light and Quantized Light and Quantized EnergyEnergy

Objectives:

• Recall that in Rutherford's model, the atom’s mass is concentrated in the nucleus and electrons move around it.

• The model doesn’t explain how the electrons were arranged around the nucleus.

• The model doesn’t explain why negatively charged electrons aren’t pulled into the positively charged nucleus.

The Atom and The Atom and Unanswered QuestionsUnanswered Questions

The Atom and The Atom and Unanswered QuestionsUnanswered Questions

• In the early 1900s, scientists observed certain elements emitted visible light when heated in a flame.

• Analysis of the emitted light revealed that an element’s chemical behavior is related to the arrangement of the electrons in its atoms.

• In order to understand this relationship and the nature of atomic structure, it will be helpful to first understand the nature of light.

Wave Nature of LightWave Nature of Light

Electromagnetic radiation, a form of energy that exhibits wave-like behavior as it travels through space.

• Visible light

• Microwaves

• X-rays

• Radio waves


• The wavelength (λ) is the shortest distance between equivalent points on a continuous wave. (crest to crest, trough to trough)

• The frequency (ν) is the number of waves that pass a given point per second.

• Hertz- SI unit for frequency= one wave/sec

• Energy increases with increasing frequency

All waves can be described by several characteristics.


• The amplitude is the wave’s height from the origin to a crest.

• Independent of wavelength and frequency

All waves can be described by several characteristics.



The speed of light (3.00 108 m/s) is the product of it’s wavelength and frequency c = λν.


• All electromagnetic waves, including visible light travels at 3.00 x 108m/s in a vacuum.

• Speed is constant but wavelengths and frequencies vary.

• Sunlight contains a continuous range of wavelengths and frequencies.

• A prism separates sunlight into a continuous spectrum of colors.


• The electromagnetic spectrum includes all forms of electromagnetic radiation.

• Not just visible light.


Practice ProblemsPractice Problems

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Particle Nature of LightParticle Nature of Light

The wave model of light cannot explain all of light’s characteristics.

• Matter can gain or lose energy only in small, specific amounts called quanta.

• A quantum is the minimum amount of energy that can be gained or lost by an atom.


Max Planck (1858-1947) – matter Max Planck (1858-1947) – matter can gain or lose energy only in can gain or lose energy only in small amounts.small amounts.• E=hv

• Planck’s constant has a value of 6.626 10–34 J ● s.

• Energy can only be emitted or absorbed in whole number multiples of h.


• The photoelectric effect is when electrons are emitted from a metal’s surface when light of a certain frequency shines on it.


• Albert Einstein proposed in 1905 that light has a dual nature. Nobel prize in 1921.

• A beam of light has wavelike and particlelike properties.

• A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy.

Ephoton = h Ephoton represents energy.h is Planck's constant. represents frequency.


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Atomic Emission Atomic Emission SpectrumSpectrum

The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element.

• Emission lines are specific to an element and can be used for identification.


• Light in a neon sign is produced when electricity is passed through a tube filled with neon gas and excites the neon atoms. The excited atoms emit light to release energy.



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ObjectivesObjectives

Compare the wave and particle Compare the wave and particle natures of light.natures of light.


Define a quantum of energy, Define a quantum of energy, and explain how it is related to and explain how it is related to an energy change of matter.an energy change of matter.


Contrast continuous Contrast continuous electromagnetic spectra and electromagnetic spectra and atomic emission spectra.atomic emission spectra.

Question?Question?

What is the smallest amount of energy that can be gained or lost by an atom?

A. electromagnetic photon

B. beta particle

C. quanta

D. wave-particle

What is a particle of electromagnetic radiation with no mass called?

A. beta particle

B. alpha particle

C. quanta

D. photon

Question?Question?

Quantum Theory of Quantum Theory of the Atomthe Atom

Quantum Theory of the Quantum Theory of the AtomAtom

• Compare the Bohr and quantum mechanical models of the atom.

• Explain the impact of de Broglie's wave article duality and the Heisenberg uncertainty principle on the current view of electrons in atoms.

• Identify the relationships among a hydrogen atom's energy levels, sublevels, and atomic orbitals.

Objectives:

Bohr’s Model of the Bohr’s Model of the AtomAtom

Bohr correctly predicted the frequency lines in hydrogen’s atomic emission spectrum.

• The lowest allowable energy state of an atom is called its ground state.

• When an atom gains energy, it is in an excited state.


• Bohr suggested that an electron moves around the nucleus only in certain allowed circular orbits.

•The smaller the electrons orbit the lower the atoms energy state or level


• Bohr suggested that an electron moves around the nucleus only in certain allowed circular orbits.

•The larger the electron’s orbit the higher the atoms energy state or level.


• Each orbit was given a number, called the quantum number. The orbit closed to the nucleus is n=1


• Example: Hydrogen’s single electron is in the n = 1 orbit in the ground state. Atom does not radiate energy.

• When energy is added, the electron moves to the n = 2 orbit. Atom is excited. (Ya, know the other kind of excited.)

• When electron moves from an excited state to ground state, a photon is emitted.


• Change in Energy =

E (higher energy orbit) – E (lower energy orbital)

Ephoton = hv

Bohr’s ModelBohr’s Model of the Atom of the Atom


Quantum Mechanical Quantum Mechanical ModelModel

The Quantum Mechanical Model of the Atom – this model progressed through a series of scientific findings:

• Louis de Broglie (1892–1987) hypothesized that particles, including electrons, could also have wavelike behaviors.

• Like vibrating guitar strings – multiples of half waves.

• Orbiting electron – odd number of wavelengths.

Quantum Mechanical ModelQuantum Mechanical Model


• The de Broglie equation predicts that all moving particles have wave characteristics.

represents wavelengthsh is Planck's constant.m represents mass of the particle. represents frequency.


Heisenberg showed it is impossible to take any measurement of an object without disturbing it.

• The Heisenberg uncertainty principle states that it is fundamentally impossible to know precisely both the velocity and position of a particle at the same time.

• Means that it is impossible to assign fixed paths for electrons like the circular orbits as previously thought.


Heisenberg showed it is impossible to take any measurement of an object without disturbing it.

• The Heisenberg uncertainty principle states that it is fundamentally impossible to know precisely both the velocity and position of a particle at the same time.

• The only quantity that can be known is the probability for an electron to occupy a certain region around the nucleus.



Schrödinger treated electrons as waves in a model called the quantum mechanical model of the atom.

• Schrödinger’s equation applied equally well to elements other than hydrogen.

• Both models limit an electron’s energy to certain values. Unlike the Bohr model, the quantum mechanical model makes no attempt to describe the electron’s path around the nucleus.


Schrödinger treated electrons as waves in a model called the quantum mechanical model of the atom.

• Electrons are located around the nucleus at a position that can be described only by a probability map. A boundary surface is chosen to contain the region that the electron can be expected to occupy 90% of the time.


• The wave function predicts a three-dimensional region around the nucleus called the atomic orbital.

Quantum Numbers and Quantum Numbers and the Revised Modelthe Revised Model

The revised model defines the The revised model defines the relationship between an electron’s relationship between an electron’s energy level, sublevel and atomic energy level, sublevel and atomic orbitals.orbitals.Four quantum numbers make up Four quantum numbers make up

the identification of each electron the identification of each electron in an atom. in an atom.

Atomic OrbitalsAtomic Orbitals

• Principal quantum number (n) indicates the relative size and energy of atomic orbitals.

n specifies the atom’s major energy levels, called the principal energy levels.


• Energy sublevels (s,p,d or f) are contained within the principal energy levels.


• n= # of sublevels per principal energy levels.


• Each energy sublevel relates to orbitals of different shape.


• Each orbital can contain 2 electrons



Compare the Bohr and quantum Compare the Bohr and quantum mechanical models of the mechanical models of the atom.atom.


Explain the impact of de Broglie's wave Explain the impact of de Broglie's wave article duality and the Heisenberg article duality and the Heisenberg uncertainty principle on the current uncertainty principle on the current view of electrons in atoms.view of electrons in atoms.


Identify the relationships among a Identify the relationships among a hydrogen atom's energy levels, hydrogen atom's energy levels, sublevels, and atomic orbitals.sublevels, and atomic orbitals.

Question?Question?

Which atomic suborbitals have a “dumbbell” shape?

A. s

B. f

C. p

D. d

QuestionQuestion

Who proposed that particles could also exhibit wavelike behaviors?

A. Bohr

B. Einstein

C. Rutherford

D. de Broglie


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Electron ConfigurationElectron Configuration


Objectives:Objectives:

• Apply the Pauli exclusion principle, the aufbau principle, and Hund's rule to write electron configurations using orbital diagrams and electron configuration notation.

• Define valence electrons, and draw electron-dot structures representing an atom's valence electrons.


The arrangement of electrons in the atom is called the electron configuration.


Three rules/ principals define how electrons can be arranged in atom’s orbitals.

1. The aufbau principle states that each electron occupies the lowest energy orbital available.



2. The Pauli exclusion principle states that a maximum of two electrons can occupy a single orbital, but only if the electrons have opposite spins.

• Electrons in orbitals can be represented by arrows in boxes and each electron has an associated spin.


3. Hund’s rule states that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same energy level orbitals.

Electron ArrangementElectron Arrangement

-Electron arrangement can be -Electron arrangement can be represented by two common represented by two common different methods. different methods. •Orbital Diagram – boxes labeled with principle energy level and sublevel associated with each orbital. Arrows are drawn up and down in the box to represent electrons and their spins.

Electron ArrangementElectron Arrangement

-Electron arrangement can be -Electron arrangement can be represented by two common represented by two common different methods. different methods. •Electron Configuration Notation- lists the following in order: Principle energy number, sublevel, superscript of number of electrons in the sublevel. Electron distribution follows the main three rules.

•Noble Gas Notation – abbreviated electron configuration by substituting noble gas symbols for a long series of notation.




• The electron configurations (for chromium, copper, and several other elements) reflect the increased stability of half-filled and filled sets of s and d orbitals.

• Some energy levels overlap. Exceptions for this start at Vandium, atomic #23.


Page 160 #21-26Page 160 #21-26

Valence ElectronsValence Electrons

• Valence electrons are defined as electrons in the atom’s outermost orbitals—those associated with the atom’s highest principal energy level.

• Electron-dot structure consists of the element’s symbol representing the nucleus, surrounded by dots representing the element’s valence electrons.

Electron Dot StructureElectron Dot Structure

Electrons are placed one at a time on Electrons are placed one at a time on the four sides of the symbol and then the four sides of the symbol and then paired until used up. Side order paired until used up. Side order doesn’t matter.doesn’t matter.Example: Example:

NaNa

ClCl

Valence ElectronsValence Electrons


Apply the Pauli exclusion principle, the aufbau Apply the Pauli exclusion principle, the aufbau principle, and Hund's rule to write electron principle, and Hund's rule to write electron configurations using orbital diagrams and configurations using orbital diagrams and electron configuration notation.electron configuration notation.


Define valence electrons, and draw Define valence electrons, and draw electron-dot structures representing electron-dot structures representing an atom's valence electrons.an atom's valence electrons.

Question?Question?

In the ground state, which orbital does an atom’s electrons occupy?

A. the highest available

B. the lowest available

C. the n = 0 orbital

D. the d suborbital

Question?Question?

The outermost electrons of an atom are called what?

A. suborbitals

B. orbitals

C. ground state electrons

D. valence electrons


Page 162 #26-33Page 162 #26-33

Study Guide Study Guide Key Concepts

• All waves are defined by their wavelengths, frequencies, amplitudes, and speeds. c = λν

• In a vacuum, all electromagnetic waves travel at the speed of light.

• All electromagnetic waves have both wave and particle properties.

• Matter emits and absorbs energy in quanta.Equantum = hν

Study Guide Study Guide

Key Concepts

• White light produces a continuous spectrum. An element’s emission spectrum consists of a series of lines of individual colors.


• Bohr’s atomic model attributes hydrogen’s emission spectrum to electrons dropping from higher-energy to lower-energy orbits.

∆E = E higher-energy orbit - E lower-energy orbit = E photon = hν

• The de Broglie equation relates a particle’s wavelength to its mass, its velocity, and Planck’s constant. λ = h / mν

• The quantum mechanical model of the atom assumes that electrons have wave properties.

• Electrons occupy three-dimensional regions of space called atomic orbitals.


• The arrangement of electrons in an atom is called the atom’s electron configuration.

• Electron configurations are defined by the aufbau principle, the Pauli exclusion principle, and Hund’s rule.

• An element’s valence electrons determine the chemical properties of the element.

• Electron configurations can be represented using orbital diagrams, electron configuration notation, and electron-dot structures.

Chapter QuestionsChapter Questions

The shortest distance from equivalent points on a continuous wave is the:

A. frequency

B. wavelength

C. amplitude

D. crest


The energy of a wave increases as ____.

A. frequency decreases

B. wavelength decreases

C. wavelength increases

D. distance increases

Chapter QuestionChapter Question

Atom’s move in circular orbits in which atomic model?

A. quantum mechanical model

B. Rutherford’s model

C. Bohr’s model

D. plum-pudding model

Chapter QuestionChapter Question

It is impossible to know precisely both the location and velocity of an electron at the same time because:

A. the Pauli exclusion principle

B. the dual nature of light

C. electrons travel in waves

D. the Heisenberg uncertainty principle

Chapter Assessment 5Chapter Assessment 5

How many valence electrons does neon have?

A. 0

B. 1

C. 2

D. 3


Spherical orbitals belong to which sublevel?

A. s

B. p

C. d

D. f


What is the maximum number of electrons the 1s orbital can hold?

A. 10

B. 2

C. 8

D. 1


In order for two electrons to occupy the same orbital, they must:

A. have opposite charges

B. have opposite spins

C. have the same spin

D. have the same spin and charge


How many valence electrons does boron contain?

A. 1

B. 2

C. 3

D. 5


What is a quantum?

A. another name for an atom

B. the smallest amount of energy that can be gained or lost by an atom

C. the ground state of an atom

D. the excited state of an atom

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Figure 5.11 Balmer Series

Figure 5.12 Electron Transitions

Table 5.4 Electron Configurations and Orbital Diagrams for Elements 1–10

Table 5.6 Electron Configurations and Dot Structures

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Chem chapt 5

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