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Understanding Electrons in Matter: Energy Levels, Valence, and Light Emission

Explore the behavior of electrons in matter, from Bohr's model to valence electrons to emission spectra. Learn how energy levels influence an element's properties and delve into the fascinating world of the electromagnetic spectrum.

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Understanding Electrons in Matter: Energy Levels, Valence, and Light Emission

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  1. Chapter 2 Matter is Made of Atoms 2.2 Electrons in Atoms

  2. Objective Objectives: Relate the electron to modern atomic theory, Compare electron energy levels in an atom, Illustrate valence electrons by Lewis electron dot structures

  3. Electrons in motion • Electrons are in motion in the outer part of an atom • When two atoms come near, these electrons interact • Electrons and their arrangement in the atom greatly affect an element’s properties and behavior

  4. Electrons in motion • Niels Bohr (early 20th century)- Proposed e-‘s must have enough energy to keep them in constant motion around the nucleus (enables e-‘s to overcome the attraction of the positive nucleus) • Bohr’s model (1913)- Planetary model The well-defined orbits are not correct. Electron motion within an atom is irregular and an electron may be close to the nucleus at times.

  5. Electromagnetic spectrum • Electromagnetic radiation (radiant energy) travels in the form of waves- have both electrical and magnetic properties • Electromagnetic waves can travel through empty space Ex: radiant energy from the sun travels to Earth

  6. Electromagnetic spectrum • Electromagnetic waves travel through space at the speed of light, approx. 300 million meters/sec

  7. Electromagnetic spectrum • Properties of waves: Frequency and wavelength Frequency-number of vibrations/ second (Hertz-Hz) Wavelength- distance between two corresponding points on two consecutive waves • Wavelength is determined by frequency Low frequency = long wavelength (low energy) High frequency = short wavelength (high energy)

  8. Electromagnetic spectrum

  9. Electromagnetic spectrum • All the forms of radiant energy are parts of a whole range of electromagnetic radiation • The electromagnetic spectrum includes gamma rays, X rays, ultraviolet (UV), Visible, Infrared (IR), microwaves, radio waves

  10. Electromagnetic spectrum

  11. Electromagnetic spectrum • Gamma Rays- highest frequency, shortest wavelength, most energetic waves, can pass through most substances • X rays- lower frequency than gamma, but still high energy waves, can pass through soft body tissue, but stopped by bone • Ultraviolet-slightly more energetic than visible, can cause sunburns, mostly absorbed by ozone

  12. Electromagnetic spectrum • Visible- part of the spectrum to which our eyes are sensitive, Our eyes and brains interpret different frequencies as different colors ROY G BIV - Newton Red- low energy Violet- high energy

  13. Electromagnetic spectrum • Infrared- less energy than visible, given off by most “warm objects” • Microwaves/ Radio waves- lowest frequency

  14. Electrons and Light • EMISSION SPECTRUM: Spectrum of light released from excited atoms of an element • Electrons can have only certain amounts of energy • Electrons can move around the nucleus only at distances that correspond to those amounts of energy • When e- absorb energy, they move to a higher energy state • When they fall back to a lower energy state- they emit energy (Light)

  15. Electrons and Light ENERGY LEVEL: Region of space in which e-‘s can move about the nucleus of an atom ELECTRON CLOUD: Space around the nucleus of an atom where the atom’s e-‘s are found Each energy level can hold a limited number of electrons http://www.youtube.com/watch?v=QI50GBUJ48s&safety_mode=true&persist_safety_mode=1&safe=active

  16. # of electrons in each level • Lowest energy level is the smallest and closest to the nucleus, Holds two electrons max • Second energy level is larger because it is farther away, Holds eight electrons max • Max # of e-‘s: 2, 8, 8,18, 32, 50, 78, 91

  17. # of electrons in each level • Bohr Model Examples: H-1 (1 p, 1 e, 0 n) Li-7 (3 p, 3 e, 4 n) 0-16 (8 p, 8 n, 8 e)

  18. VALENCE ELECTRONS • The electrons in the outermost energy level • Valence electrons are important because they interact when atoms come near each other • Chemical and physical properties of an element are directly related to the number and arrangement of valence electrons (v.e.)

  19. VALENCE ELECTRONS • Atoms in group 1 have one valence electron • Atoms in group 2 have two valence electrons • Atoms in group 13 have three valence electrons • Atoms in group 14 have four valence electrons • Atoms in group 15 have five valence electrons • Atoms in group 16 have six valence electrons • Atoms in group 17 have seven valence electrons • Atoms in group 18 have eight valence electrons

  20. LEWIS DOT DIAGRAM • Illustrates valence electrons as dots around the chemical symbol of an element. • Each dot represents one valence electron (max # of v.e. is 8) • The symbol represents the core of the atom. Ex: . . Li  Be  B 

  21. LEWIS DOT DIAGRAM • Li has 2 e- in the first energy level and 1 in the second, • Be has 2 e- in the first energy level and 2 in the second, • B has 2 e- in the first energy level and 3 in the second • More examples: C, N, O, F, Ne

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