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

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Unit 9 : Atomic Theory and Periodicity

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Unit 9 atomic theory and periodicity

Unit 9: Atomic Theory and Periodicity

Section 2: Quantum Mechanical Theory


Problems with the bohr model

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

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

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)


The second quantum number

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 number1

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

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

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


Quantum number relationships in atomic structure

Quantum Number Relationships in Atomic Structure


Electron configuration

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

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 element silver has 47 electrons

    • 1s22s22p63s23p64s23d104p65s24d9


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