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Unit 9 : Atomic Theory and PeriodicityPowerPoint Presentation

Unit 9 : Atomic Theory and Periodicity

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### 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
- 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

Quantum Numbers

- 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

The First Quantum Number

- 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)

- In energy level 1, there is only

The Second Quantum Number

- 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

The Second Quantum Number

- 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.

The Third Quantum Number

- Magnetic quantum number (m)
- Determines the orientation of an orbital around the nucleus
- Has values ranging from –l through 0 to +l

The Fourth Quantum Number

- 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

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

Electron Configuration

- A way of describing each of an element’s electrons
- Written using the following steps:
- Find out the # of electrons for the element
- Start with the 1s part
- 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)

Electron Configuration Examples

- 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 sum of the superscript #s equal 11

- 1s22s22p63s1
- The element silver has 47 electrons
- 1s22s22p63s23p64s23d104p65s24d9

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