Chapter 4 Arrangement of Electrons in Atoms. 4-1 The Development of the New Atomic Model...
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Transcript of Chapter 4 Arrangement of Electrons in Atoms. 4-1 The Development of the New Atomic Model...
Chapter 4
Arrangement of Electrons in Atoms
4-1 The Development of the New Atomic Model
•Rutherford’s atomic model – nucleus surrounded by fast-moving electrons- not complete model
•Electromagnetic Radiation- form of energy that exhibits wavelike behavior
•Ex: visible light, microwaves, x-rays
Wave Nature of Light
•Electromagnetic Spectrum- encompasses all forms of EM radiation
Electromagnetic Spectrum
•Wavelength (λ )- shortest distance between equivalent points on a continuous wave
•Measured crest to crest or trough to trough
•Frequency (ν )- number of waves that pass a given point per second
•1 Hertz (Hz) = 1 wave per second; SI unit of frequency
•Amplitude- wave’s height from the origin to a crest or from origin to trough
•Speed of light = wavelength x frequency
•C = λν
•Photoelectric Effect- electrons are emitted from a metal’s surface when light of a certain frequency shines on the surface
•Ex: calculator with photoelectric cell
Particle Nature of Light
•Quantum concept- produces glowing light of hot objects
•Quantum- minimum amount of energy that can be gained or lost by an atom
•Equantum = hv
•E = energy•V = frequency•h = Planck’s constant;
6.626 x 10-34 J•s•J is joule; SI unit for energy
•Photon- particle of EM radiation with no mass that carries a quantum of energy
•Ephoton = hv
•Ground State- lowest allowable energy state of an atom
•Excited State- when an atom gains energy
•Line Emission Spectrum- set of frequencies of the EM waves emitted by atoms of the element
•Unique to each element, used for identification
•Continuous spectrum
•Bohr Model of the Atom- proposed that hydrogen atom has only certain allowable energy states
Sect. 4-2: The Quantum Model of the Atom
• Electrons as waves…De Broglie applies light’s wave-particle duality to electrons/Bohr’s model
• Heisenberg Uncertainty Principle – impossible to know position and velocity at same time
• Schrödinger wave equation
• Quantum theory – describes mathematically the wave properties of electrons
• Orbital – probable location of electron around nucleus
Atomic Orbitals and Quantum numbers
• Quantum numbers – specify properties of atomic orbitals and electrons in orbitals• solutions to Schrödinger wave
equation
• Principal quantum number (n) – represents main energy level (shell) & tells how many sublevels• Positive integers (1,2,3,etc.)• Total # orbitals per shell = n2
• Total # electrons per shell =2n2
• Angular momentum quantum number (l) – indicates shape of orbital (sublevel)• l = zero and all positive integers
less than or equal to n-1• l=0, s orbital (spherical)• l=1, p orbital (dumbbell)• l=2, d orbital• l=3, f orbital
• Magnetic quantum number (m) – indicates the orientation of orbital around nucleus• range from -2 to +2, depending on
sublevels
• Spin Quantum number – indicates spin state of electron• can only equal ½ or -½ • orbital holds 2 max electrons & they
must have opposite spins
Sect. 4-3: Electron Configurations
• Electron configuration – arrangement of electrons in an atom
Rules for Electron Configurations• Aufbau principle – lowest energy
level fills first• Pauli exclusion principle –
electrons in same orbital, opposite spin
• Hund’s rule – orbitals of equal energy must all have 1 electrons before a second can be added
• Orbital Notation (Diagram) – lines, arrows, principal quantum #, and sublevel letter
• Electron Configuration Notation – principal quantum #, sublevel letter, and superscript (# e-)
• Noble Gas Notation – shortened version of electron configuration notation
• Deviations from normal electron configurations (more stable with pulling one from s to half-fill or fill d)• Chromium• Copper