Presentation on theme: "Chapter 7: Completing the Model of the Atom"— Presentation transcript:
1 Chapter 7: Completing the Model of the Atom Section 7.1: Expanding the Theory of the Atom
2 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
3 Energy levelsElectrons with the most energy are farthest from the nucleus and occupy the outermost level
4 Review of Electromagnetic Radiation and Energy levels Waves have a range of freq. and wavelengthsHigher freq = Shorter wavelength = Greater energyLower freq = Longer wavelength = Lower energy
5 Review of Electromagnetic Radiation and Energy levels (cont) Use to calculate the exact amount of energy released by electrons in atomsBy absorbing a specific amount of energy, an e- can jump to a higher energy levelWhen 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 frequencyThe energy (color) of light depends on how far the electron fallsGreater energy = Color more toward the violet end of spectrum
7 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
8 Electron cloud modelBecause 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
9 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.
10 Quantum NumbersThere are 4 quantum numbers that describe the electron distribution of electrons in an atom They are n, l, m and s
11 Principal quantum number, n Describes the general size of the electron cloudNumbered levels low to high – 1,2,3,4…(integers)Electrons may be found in eachThe maximum # of electron possible in any one level is 2n2We have been calling these energy levels, 1-7Each main energy level has sublevels
12 Angular quantum number, l Describes the shape of the electron cloudIt represents the sublevels within an energy levelThe value of l is 0 to (n-1)The number of sublevels is equal to the value of nThe lowest sublevel is s, then p, d and f
13 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.
17 Magnetic Quantum Number, m Describes the orientation in space of a particular orbitalThe value is any integer between +l and -l
18 Electron Spin Quantum Number, s Describes the spin of the electron within an orbitalThe value is +1/2 (clockwise) or -1/2 (counterclockwise)If there are 2 electrons in an orbital, they must spin in opposite directions.
19 Hund’s RuleIn 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.