Atomic Structure and Electronic Configuration, Lecture notes of Chemistry

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2. Atomic Structure

Electromagnetic Spectrum: The electromagnetic spectrum is the range of frequencies of electromagnetic radiation and their respective wavelengths. As the wavelength decreases, frequency and energy increase. Emission spectrums: An emission spectrum is the pattern of lines formed when light passes through a prism to separate it into the different frequencies. Types of spectrums: Line spectrum: Only sharp, discrete colors Continuous spectrum: All colors Emission spectra are produced when photons are emitted from atoms as excited electrons return to a lower energy level. Process: ● After an electron is stimulated (e.g., by radiation), it becomes excited ● It moves from its original orbit to an outer orbit. The process is also known as absorption ● Then it returns to its original orbit, and releases energy in the form of a photon ● The photon releases its transition from a higher energy level to a lower energy level corresponding to a certain wavelength. ● Emission (line) spectrums are produced by excited atoms as they fall back to a lower energy level and only contain specific colors (wavelengths, frequencies) of visible light

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n = 2 Lyman^

(UV (^) light) (^) highest energy n= 1 S

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freq

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to lower

energy levels

O

O

emission absorbtin

high amount (^) of energy emitted => shorter

wavelength

·

B &^ D^ are^ Sabsorption

not emission · choice^ blu^ A &^ C n: 1 -^ >^ n^ = 3 shorter (^) radiation tha n = 2 =^ n= 1 => longest wavelength C

s s p s p s d p s d p s f d p s f d p Orbitals: ● No more than two electrons can occupy any one orbital and if two electrons are in the same orbital they must spin in opposite directions (Pauli’s Exclusion Principle) ● Electrons are placed into orbitals of lowest energy first (Aufbau Principle) ● Orbitals of the same sub-level are filled singly first, then doubly. If more than one orbital in a sub-level is available, electrons occupy different orbitals with parallel spins (Hund’s Third Rule). ● There are four main energy levels ● Each main energy level is divided into several sub-levels ● Sub-levels contain a fixed number of orbitals , regions in space where electrons are likely to be found. ● Sub-level is a group of orbitals with particular properties like shape and angular momentum ● Orbitals can take up to 4 different shapes s-orbitals take a spherical shape p-orbitals resemble a “dumbbell” shape ● Every orbital can hold up to two electrons maximum: ○ s: 1 orbital, 2 electrons ○ p: 3 orbitals, 6 electrons ○ d: 5 orbitals: 10 electrons ○ f: 7 orbitals, 14 electrons ·

ven

affinity (AE)^

is (^) exothermic

(negative values)^

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