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Atomic Theory continues…

Where are the electrons?. Atomic Theory continues…. What we already know…. Democritus developed the concept of the atom. Dalton identified it as a solid, indivisible mass. Thomson described it as “Plum Pudding”. Rutherford said it has a nucleus containing protons and neutrons.

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Atomic Theory continues…

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  1. Where are the electrons? Atomic Theory continues…

  2. What we already know… • Democritus developed the concept of the atom. • Dalton identified it as a solid, indivisible mass. • Thomson described it as “Plum Pudding”. • Rutherford said it has a nucleus containing protons and neutrons. • But, no one has said anything about where the electron is…

  3. Bohr’s Model • …until Niels Bohr (1913) • Bohr developed what came to be known as the “Planetary Model”. • Described the electrons as moving around the nucleus in concentric circular paths called orbits. • Each orbit requires a specific amount of energy for an electron to travel its path. (Energy Level)

  4. Planetary Model

  5. Bohr’s Model • There is also a specific amount of energy required to move from one orbit to another. (Quantum) • As electrons move into orbits further from the nucleus, • Their increased energy and decreased attraction to the protons allow them to leave the atom more easily. • It is much more difficult for atoms close to the nucleus to leave the atom than those that are farther away.

  6. Bohr’s Model gets tested… • Erwin Schrödinger attempted to follow the path of an electron through an atom to graph the orbits. • He started with the simplest atom • Hydrogen – 1 electron • Plotted points representing the location of the electron at various times. • His graph did NOT look like a circle…(which is what they expected)

  7. Schrödinger’s Plot of Hydrogen

  8. A New View • With this new information, Schrödinger identified a probability area where the electron traveled. • Probability area became known as an ORBITAL. • Schrödinger and friends identified several different probability areas and therefore needed a new model.

  9. Quantum Mechanical Model • Uses a series of 4 numbers to identify the probability area for each electron in an atom. • Each electron has its own set of 4 numbers. • 4 numbers are the QUANTUM NUMBERS

  10. Quantum Numbers • Principle Quantum Number (n) • Refers to main ENERGY LEVELS • Identifies the distance from the nucleus • n = 1, 2, 3, 4, 5, 6, 7 • Sublevel • Refers to the orbital • Identifies the shape of the probability area • s, p, d, f

  11. Quantum Numbers • Orientation in 3D • Refers to the axes • Identifies the position of the area in 3D • X, Y, Z or combination such as XY • Spin • Refers to the direction of spin • Identifies spin as either clockwise or counterclockwise • +1/2, -1/2 or , 

  12. Quantum Numbers Things to know • The number of electrons that can fit in any single energy level can be found using the following formula: e- = 2n2 • Ex. Energy level 1 (n=1) has 2 electrons • Ex. Energy level 2 (n=2) has 8 electrons • The number of sublevels in an energy level is equal to the number of the energy level. • Ex. Energy level 1 has 1 sublevel • Ex. Energy level 2 has 2 sublevels

  13. Quantum Numbers Things to know • Sublevels are always used in this order • s, p, d, then f • Each sublevel has a different shape • S is spherical • P is “dumb-bell” shaped • D is “clover leaf” shaped • F is complex

  14. Sublevel shapes

  15. Sublevel shapes

  16. Sublevels combined… • Energy Level 1 • Energy level 2 • Energy level 3

  17. Quantum Numbers Things to know • Each sublevel has a different number of orbitals. • s has 1 • p has 3 • d has 5 • f has 7 • Each orbital can only contain 2 electrons. • If 2 electrons are in a single orbital, they must have opposite spin. • Each sublevel must be filled with electrons BEFORE moving on to the next sublevel.

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