Unit 1 – Atomic StructureLesson 1: The Electromagnetic Spectrum

Wavelength & Frequency• Wavelength– Measured in nm distance between 2 peaks

• Frequency• Measured in Hz # of wavelengths passing a given point in

a second

Electromagnetic Spectrum

• As wavelength decreases, frequency increases

Types of Radiation• Gamma Rays– Highest frequency– Sources: nuclear reactions,

outer space– Have enough penetrating

ability to pass through 3 meters (9 feet!) of concrete

– In large amounts can cause radiation poisoning

– When controlled, can be used to help cure some cancers

• X-Rays– Extensively used in the medical field – Uncontrolled exposure to x-rays, can lead to

mutations or cell damage– Used by geologists & chemists for characterizing

the structure & properties of crystalline materials

Types of Radiation

• UV – Some exposure

promotes Vitamin D production and tanning

– Too much can lead to sunburn, retina damage and cancer

Types of Radiation

More UV uses

– Kills micro-organisms in water and food– Hardens casts – Insects & birds use UV for navigation

• Infrared (IR)– Molecules existing above

absolute zero (-273 Celsius) all emit IR, recorded as heat

– ½ of the Sun’s energy is emitted in the IR region

– Tungsten light bulbs are inefficient. They produce more IR than actual visible light

Types of Radiation

Infrared Cont’d

Types of Radiation• Microwaves– Highest frequency– Emitted by Earth, buildings, cars, planes– Low level radiation in space

• Radio waves

Types of Radiation

Types of Radiation• Visible light (radiation our eyes see)– Ranges from 780 nanometers (deep red) to 400

nanometers (violet)– ROYGBIV– Also called a “continuous spectrum

Visible light cont’d

Visible light cont’d• Electrons travel in specific orbits• Emit light when they give off the energy they

acquired & fall back to their original orbit

Spectroscopy

• Emission– Study of the line spectra given off by electrons

returning to their original energy level• Absorption– Study of the dark lines of a spectra which

represents the energy that was absorbed by a sample

The Glowing Pickle!

• http://www.youtube.com/watch?v=QZieGLO9_ks

Historical Development of The Atomic Model

• John Dalton (1766-1844)– English school teacher,

interested in chemistry, physics and meteorology

– Developed atomic theory– Published the first list of

atomic weights– Died in 1844 after suffering

from repeated strokes for over 7 years, although he continued to contribute effectively to science

Dalton’s Atomic Theory

1. All elements are composed of tiny, indivisible particles called atoms

2. Atoms of the same element are identical and those of different elements are different

3. Atoms of different elements can physically mix together or chemically combine in simple whole number ratios to form compounds

4. While chemical reactions occur when atoms are separated, joined, or rearranged, atoms of one element are never changed into atoms of another element as a result of a chemical reaction

JJ Thomson (1856-1940)

• Plum pudding model

Ernest Rutherford (1871-1937)“gold foil experiment”

Neils Bohr (1885-1962)

• Proposed electrons are arranged in orbits

-Electrons cannot exist between energy levels-To move up an energy level an electron must gain enough electricity-When it loses this acquired energy, it moves back down to its original energy level

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Energy Levels

Louis de Broglie (1892-1987)• Wave particle theory• Related circumference of

orbit to whole number wavelengths of an electron travelling around the nucleus

Erwin Schrodinger (1887-1961

• Defined the probability of finding an electron around the nucleus