Electrons in Atoms Section 2.2

Niels Bohr (Born in Denmark 1885-1962) Student of Rutherford

Niels Bohr’s Model He proposed that electrons have enough energy to keep them in constant motion around the nucleus. Electrons have energy of motion that enables them to overcome the attraction of the positive nucleus.

Niels Bohr’s Model (1913) Electrons orbit the nucleus in circular paths of fixed energy (energy levels). Called the Planetary model.

Electromagnetic Spectrum Electromagnetic Spectrum is a range of electromagnetic radiation. Electromagnetic waves can travel through empty space. Properties of waves: Frequency: The number of vibrations per second. The unit is the Hertz (Hz). Wavelength: The distance between corresponding points on two consecutive waves.

Electromagnetic Spectrum TEXTBOOK Page 70

Electromagnetic Wave

Electrons & Light Emission Spectrum: The spectrum of light released from excited atoms. Each element has a different emission spectrum.

Niels Bohr’s Atom When electrons absorb energy they become “excited” and move to higher energy levels. When electrons fall back to lower energy levels, they give off energy in the form of light.

Energy Levels Energy levels are regions of space in which electrons can move about the nucleus. ● Energy levels are like the rungs of a ladder but are not equally spaced. Electrons cannot hover between energy levels, they must absorb enough energy to move to the higher level.

The Electron Cloud Model The electron cloud model is the space around the nucleus of an atom where the atom’s electrons are likely to be found.

Valence Electrons Valence electrons are the electrons in the outermost energy level. Many chemical and physical properties of an element are directly related to the number and arrangement of valence electrons.

Valence Electrons You can use the periodic table to predict the number of valence electrons. Red Dots = Valence Electrons

Lewis Dot Diagram Lewis dot diagrams illustrate valence electrons as dots around the chemical symbols of an element. Each dot represents one valence electron.

Aurora Borealis The aurora borealis (the Northern Lights) and the aurora australis (the Southern Lights) have always fascinated mankind, and people even travel thousands of miles just to see the brilliant light shows in the earth's atmosphere. The auroras, both surrounding the north magnetic pole (aurora borealis) and south magnetic pole (aurora australis) occur when highly charged electrons from the solar wind interact with elements in the earth's atmosphere. Solar winds stream away from the sun at speeds of about 1 million miles per hour. When they reach the earth, some 40 hours after leaving the sun, they follow the lines of magnetic force generated by the earth's core and flow through the magnetosphere, a teardrop-shaped area of highly charged electrical and magnetic fields.

As the electrons enter the earth's upper atmosphere, they will encounter atoms of oxygen and nitrogen at altitudes from 20 to 200 miles above the earth's surface. The color of the aurora depends on which atom is struck, and the altitude of the meeting. Green - oxygen, up to 150 miles in altitude Red - oxygen, above 150 miles in altitude Blue - nitrogen, up to 60 miles in altitude Purple/violet - nitrogen, above 60 miles in altitude

All of the magnetic and electrical forces react with one another in constantly shifting combinations. These shifts and flows can be seen as the auroras "dance," moving along with the atmospheric currents that can reach 20,000,000 amperes at 50,000 volts. (In contrast, the circuit breakers in your home will disengage when current flow exceeds 15-30 amperes at 120 volts.) The auroras generally occur along the "auroral ovals," which center on the magnetic poles (not the geographic poles) and roughly correspond with the Arctic and Antarctic circles. http://science.howstuffworks.com/nature/climate-weather/atmospheric/question471.htm

Aurora Borealis Video (1:56) additional video (1:56)

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