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**Chapter 7: Completing the Model of the Atom**

Section 7.1: Expanding the Theory of the Atom

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**Electrons Occupy a complex world of energy levels **

electron distribution in energy levels of an atom account for many of the physical and chemical properties of the element

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Energy levels Electrons with the most energy are farthest from the nucleus and occupy the outermost level

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**Review of Electromagnetic Radiation and Energy levels**

Waves have a range of freq. and wavelengths Higher freq = Shorter wavelength = Greater energy Lower freq = Longer wavelength = Lower energy

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**Review of Electromagnetic Radiation and Energy levels (cont)**

Use to calculate the exact amount of energy released by electrons in atoms By absorbing a specific amount of energy, an e- can jump to a higher energy level When an e- falls back to a lower energy level, it releases the same amount of energy in the form of radiation (light) with a definite frequency The energy (color) of light depends on how far the electron falls Greater energy = Color more toward the violet end of spectrum

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**Heisenberg’s Uncertainty Principle**

States that it is impossible to measure exactly both the position and momentum (mass and speed) of an object (electron) This led to the electron cloud model in atoms

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Electron cloud model Because we cannot pinpoint exactly where an electron is on the “surface” of an atom, we refer to its position as an electron cloud. The chemical behavior and properties of any 2-subtances are determined by the number of these electrons around the nucleus

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**How do we describe the electron cloud?**

We use quantum numbers. These represent the energy states of the electron. These difference in energy states were “discovered” due to the different spectral lines of an emission spectrum.

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Quantum Numbers There are 4 quantum numbers that describe the electron distribution of electrons in an atom They are n, l, m and s

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**Principal quantum number, n**

Describes the general size of the electron cloud Numbered levels low to high – 1,2,3,4…(integers) Electrons may be found in each The maximum # of electron possible in any one level is 2n2 We have been calling these energy levels, 1-7 Each main energy level has sublevels

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**Angular quantum number, l**

Describes the shape of the electron cloud It represents the sublevels within an energy level The value of l is 0 to (n-1) The number of sublevels is equal to the value of n The lowest sublevel is s, then p, d and f

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**Angular quantum number, l (cont)**

Each sublevel can hold up to a specific # of electrons: s sublevel can hold 1 pair (2 electrons) p can hold 3 pair (6 electrons) d can hold 5 pair (10 electrons) f can hold 7 pair (14 electrons) Each pair has a different place in space, this space is called an orbital.

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Orbitals

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**Angular quantum number, l (cont)**

The sum of all the electron clouds in any sublevel is a spherical cloud. Electrons are repelled by each other and attracted to the positive nucleus

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**Blocks in the Periodic Table**

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**Magnetic Quantum Number, m**

Describes the orientation in space of a particular orbital The value is any integer between +l and -l

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**Electron Spin Quantum Number, s**

Describes the spin of the electron within an orbital The value is +1/2 (clockwise) or -1/2 (counterclockwise) If there are 2 electrons in an orbital, they must spin in opposite directions.

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Hund’s Rule In a set of orbitals, the electrons will fill the orbitals in a way that would give the maximum number of parallel spins (maximum number of unpaired electrons). Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

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**Orbital Diagram for Hydrogen**

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**Orbital Diagram for Helium**

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**Orbital Diagram for Lithium**

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**Orbital Diagram for Beryllium**

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**Orbital Diagram for Carbon**

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**Orbital Diagram for Nitrogen**

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**Standard Notation of Fluorine**

Number of electrons in the sub level 2,2,5 1s2 2s2 2p5 Main Energy Level Numbers 1, 2, 2 Sublevels

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