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.

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