The Periodic Table and Atomic Structure

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Chapter 6


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Visible light is a more accurate term for what we usually referto simply as light

The light that our eyes can detect comprises only a smallportion of the possible electromagnetic spectrum and accounts

for a small portion of the emission of most bulbs.

Other familiar forms of electromagnetic radiation includeradio waves, microwaves and x- rays.

The origin of the word electromagnetic lies in the nature oflight.

Historically, light has been described as a wave travellingthrough space. One component is an electric field, and another

is a magnetic field.

The Electromagnetic Spectrum


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The Electromagnetic Spectrum


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Many features of light what we encounter can be explainedas properties of waves.

The central characteristics of a wave can be defined by fourvariables:

Wavelength of any wave is the distance between corresponding pointsof adjacent waves; designated as and measured in units of length;distance between peaks.

Amplitude is the size or height of the wave

Frequency is the number of complete cycles of the wave passing agiven point per second; usually designated as and measured in unit of1/s or hertz (Hz).

Frequency and wavelength are not independent of one another.

The Wave Nature of Light


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The speed of light in a vacuum (designated by c and measuredin units of distance/time) is a constant of nature that has beenmeasured within impressive precision (c=2.99792458x108 m/s)

Because the speed of light is a constant, the number of waves

that will pass a certain point in time will be inversely related tothe wavelength.

Speed, wavelength, frequency and amplitude arecharacteristics than can describe any wave.

The wave nature of light also helps to explain many of thephenomena we experience with light.

Refraction is the bending of a wave when it passes from one

medium to another.



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When white light passes through a prism, it

separated into its constituents color by refraction


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Because wave-like phenomena such as refraction, itis common to categorize electromagnetic radiationin terms of its wavelength or frequency.

In addition to visible light, the spectrum includes X-

ray, ultraviolet (UV), infrared (IR), microwave, andradio wave radiation, the visible falls between UV

and IR.

This order lists the regions of the spectrum in

increasing length.



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Electromagnetic Spectrum


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The context in which we normally think of light as particle iswhen it is imparting energy to another object.

Albert Einstein proposed that light could behave as acollection of packets of energy called photons, when it has

energetic consequences.

Bright light has many photons, where as dim light has few.

The energy of a photon of light has been shown to be

proportional to its frequency, leading to a simple equation:E=hv; where E represents the photon energy, and v is thefrequency of light; h is a constant called Plancks constant(h=6.6262x10-34 Js)

The Particulate Nature of Light


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When an atom emits light, it is releasing energyto the surround world.

So we think about this situation in terms of the

conservation of energy.When light is emitted, the atoms goes from ahigher energy state to a lower energy state, and

the emitted photon carries away the energy lost

by the atom.

Atomic Spectra


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The Bohr Atom


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Bohrs Atomic Structure


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The Quantum

Mechanical Models
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Quantum Mechanics

According to quantum mechanics, only certain orbits areallowed (thus, the idea of a mini planetary system is notcorrect).

The orbits are identified by a principal quantum numbern, which can be related to the size, n = 0 is the smallest; n= 1, 2 .. are larger. (They are "quantized" or discrete, beingspecified by integers).

The angular momentum lis quantized, and so is the

projection in a specific direction m.The structure of the atom is determined by the Pauliexclusion principle, only two electrons can be placed in anorbit with a given n, l, mone for each spin.


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Discussion of Quantum

Mechanical Model
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Wave Mechanical Model


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Discussion of the Atomic

Structure and Periodict Table
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The size of the atom is determined largely by itsvalence electrons because they occupy theoutermost orbitals.

Two factors are important:1. The shell in which the valence electrons are found

2. The strength of the interaction between the nucleusand the valence electrons

Atomic Size


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The Periodic Tends in Atomic Properties


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Another property of atoms that plays a role in the way theyinteract in forming chemical bonds is the ease with which theylose electrons.

Insight into its periodicity and atomic structure can be

gleaned by looking at the way ionization energy varies acrossthe periods and within groups of the table.

As we move down the group, the valence electrons occupylarger and larger orbitals.

As the valence electrons move further from the nucleus, theybecome easier to remove.

So ionization energy decreases as we move down the a column

in the periodic table.

Ionization Energy


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Ionization Energy


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Ionization Energy


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Ionization energy is defined as the energy required toremove an electron from an atom, forming a positive lycharged cation.

But we also know that some atoms will routinely pick up

an electron to form a negatively charged anion.

We can define a property called electron affinity as theamount of energy we would have to supply to induce thisreaction.

Electron affinity values display periodic trends based onelectron configuration, much like the other propertiesweve been considering.

Electron Affinity


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Electronegativity
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Summarize the following insight in thechapter: Incandescent and Fluorescent Lightsand Modern Light Sources: LED and Lasers

Answer the following questions from pages242 up to 244: 6.3,6.16,6.20,6.38,6.56,6.60,6.68 and 6.76.

Individual Assignment due on Thursday

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The Periodic Table and Atomic Structure