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# Unit 9 : Atomic Theory and Periodicity - PowerPoint PPT Presentation

Unit 9 : Atomic Theory and Periodicity. Section 2: Quantum Mechanical Theory. Problems with the Bohr Model. Suggests that orbiting electrons move at a specific radius, like a planet does around the sun

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### Unit 9: Atomic Theory and Periodicity

Section 2: Quantum Mechanical Theory

• Suggests that orbiting electrons move at a specific radius, like a planet does around the sun

• We later find out that oribtals are actually electron clouds, and differ in size, shape, and orientation

• We use the quantum model to find the probability that an electron resides at a particular location

• The denser the electron cloud, the higher the probability of finding an electron in that region

• Specifies the properties of atomic orbitals and the properties of electrons in orbitals

• Each electron can be assigned a set of four quantum numbers

• These numbers are the electron’s address

• Principal quantum number (n)

• Describes the energy level

• Are positive integers beginning with 1, 2, 3, etc.

• The first energy level is closest to the nucleus, and each one after that moves farther away from the nucleus and increases in energy

• More than one electron can

have the same energy level

• The total number of orbitals

that exist is equal to n2

• In energy level 1, there is only

1 orbital (12)

• In energy level 2, there are 4

orbitals (22)

• Angular momentum quantum number (l)

• Describes the shape of the orbital as s, p, d, or f

• s, p, d, and f are called energy sublevels

• Has values from 0 to 3

• s = 0

• p = 1

• d = 2

• f = 3

• At this level, we don’t go into

much detail with the “f” sublevel

• s sublevel has one orbital, an s orbital

• A capacity of two electrons

• Makes up columns 1 and 2 on the p.t.

• p sublevel has three orbitals, x, y, and z

• A capacity of six electrons

• Makes up columns 13 to 18 on the p.t.

• d sublevel has five orbitals

• A capacity of ten electrons

• Makes up columns 3 to 12 on the p.t.

• f sublevel has seven orbitals

• A capacity of 14 electrons

• Makes up the lanthanides and actinides on the p.t.

• Magnetic quantum number (m)

• Determines the orientation of an orbital around the nucleus

• Has values ranging from –l through 0 to +l

• Spin quantum number

• Electrons are said to have either a +½ spin or a -½ spin

• Also known as a clockwise and counterclockwise spin

• Within an orbital, the first electron has a positive spin and the second electron has a negative spin

• A single orbital can hold a maximum of two electrons, which must have opposite spin states

• A way of describing each of an element’s electrons

• Written using the following steps:

• Find out the # of electrons for the element

• 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, etc.

• For each orbital, insert the maximum # of electrons in the exponent position

• Continue until each element’s electrons has been described

• The superscripts should add up to the element’s atomic # (indicates # of electrons)

• The element sodium has 11 electrons

• 1s22s22p63s1

• The sum of the superscript #s equal 11

• 2+2+6+1 = 11

• The coefficients indicate the energy level and row # on the p.t.

• The alphabet’s superscripts indicate the location and column # on the p.t.

• The element silver has 47 electrons

• 1s22s22p63s23p64s23d104p65s24d9