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Arrangement of Electrons In Atoms

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1 Arrangement of Electrons In Atoms
Objectives Explain relationship between speed, wavelength, frequency of electromagnetic radiation Discuss the wave-particle duality of light How the photoelectric effect and line-emission spectrum of hydrogen helped develop the atomic model Describe the Bohr model of the atom

2 Seeing the Light c = 3.00 x 10^8 m/s (speed of light)
Consists of particles called photons Also has wave-like properties Wavelength (λ) - distance between two corresponding points on adjacent waves Frequency (v)- # of waves that pass a point in any given amount of time

3 The Visible Spectrum Between 380nm – 750nm
Shorter wavelength is more powerful (ionizing) Blue has shortest wavelength

4 Energy of a Wave E = energy (J)
H = Planck’s constant (6.626 x 10^-34 J*s) c = 3.00 x 10^8 m/s λ = wavelength

5 The Eelectromagnetic Spectrum

6 Bohr Model of the Atom Electrons orbit nucleus at fixed distances
Electrons can only have fixed energies at these distances Each orbit called a shell and is assigned a quantum number

7 Shells Electrons in shell n = 1 have lowest energy
Each shell can hold up to 2n2 electrons Innermost shell is filled first

8 Quantum Model of the Atom
Objectives Explain how Heisenberg uncertainty principle and Shroedinger wave equation led to idea of atomic orbitals List 4 quantum numbers & their significance Relate the number of sublevels corresponding to each of an atom’s main energy levels, the number of orbitals per energy sublevel, and the number of orbitals per main energy level

9 Heisenberg Uncertainty Principle
It is impossible to simultaneously determine the location and velocity of an electron

10 Schrödinger Wave Equation
Quantum Theory – describes mathematically the wave properties of electrons and other very small particles

11 Principle Quantum Numbers
Symbolized by n Value of n are positive integers (1,2,3 etc) As n increases, so does its energy and distance from nucleus More than one e- can have the same n value Also called shells or main energy level Total number of orbitals in a shell = n2

12 Angular Momentum Quantum Number
Symbolized by l Indicate the shape of the orbital Also called sublevels Number of shapes equal to n Value of l are zero and all positive integers less than or equal to (n - 1) Example: n = 2; l = 0 or l = 1 Each integer is assigned a letter Example: 0 = s; 1 = p; 2 = d; 3 = f n = 2; there are two sublevels s and p Each orbital is designated by its principle quantum number and letter of the sublevel Example: 1s, 2s or 2p

13 Magnetic Quantum Number
Symbolized by m Represents orientation of orbital around the nucleus s orbital is spherical; has one orientation p orbital is dumbbell shaped; 3 orientations px, py, pz m = -1, m = 0, or m = 1

14 Summary (n) (l) ml # of orbitals Number of electrons (2n2) 1 1s 2 2s
Orbital Designation ml # of orbitals Number of electrons (2n2) 1 1s 2 2s 2p -1,0,1 3 6 3s 3p 3d -2,-1,0,1,2 5 10 4 4s 4p 4d 4f -3,-2,-1,0,1,2,3 7 14

15 Spin Quantum Number Only two possible values -1/2 or +1/2
Any single orbital can hold only two electrons


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