Atomic Spectra A spectroscope is an instrument that disperses the light emitted by an excited gas into the different frequencies the light contains. Light with multiple wavelengths Wavelengths separated refraction

Atomic Spectra An emission spectrum consists of the various frequencies of light given off by an excited substance. Below is the part of the emission spectra of sodium.

Atomic Spectra An absorption spectrum consists of the various frequencies absorbed by a substance when white light is passed through it. The frequencies in the spectrum of an element fall into sets called spectral series. Seen here is the spectral series of hydrogen.

Origin of Absorption Spectra

Spectrum of hydrogen When energy is supplied to the H gas sample, individual atoms absorb different amount of energy and electron shift to different energy levels, I,e., 3 rd, 4 th, 5 th ……. The electrons are in higher energy levels are relatively unstable and drop back to lower energy levels. This process of dropping back, energy is emitted in the form of line spectrum containing various lines of particular frequency and wavelength.

Spectrum of Hydrogen

Electron Waves and Orbits An electron can circle a nucleus only in orbits that contain a whole number of de Broglie Wavelengths. The quantum number n of an orbit is the number of electron waves that fit into the orbit.

Electron Waves and Orbits Electrons seemed to be locked into these wave patterns around the nucleus.

Quantum Mechanics The theory of quantum mechanics was developed by Erwin Schrödinger, Werner. According to quantum mechanics, the position and momentum of a particle cannot both be accurately known at the same time. Only its most probable position or momentum can be determined. The most probable distance between the proton and electron for a hydrogen atom turns out to be about 0.89Å, the same as Niels Bohr. 0.89Å Erwin Schrödinger ( )

Quantum Numbers and Atomic Orbitals n = principal quantum number(shell) describes orbital size specifies primary energy level greater n, higher E (like Bohr’s E) l = angular momentum quantum number (subshell)(azimuthal quantum number) describes orbital shape l = 0 = s orbital l = 1 = p orbital inc E l = 2 = d orbital within l = 3 = f orbital n

m l = magnetic quantum number describes orbital orientation the direction is space also tells the number of orbitals of same energy (degenerate orbitals) So, the combination of n, l, and m l, completely describes a specific orbital, its size, shape and orientation. To make a complete picture, a 4th quantum number added, m s. m s = spin quantum number - describes the electron spin in the orbital Quantum Numbers and Atomic Orbitals

Quantum Numbers principal quantum number n 1,2,3,….. orbital quantum number l 0,1,2,….n-1 magnetic quantum number m -l to +l for n=2 -2,-1,0,1,2 spin magnetic quantum number +½ or –½ spin Its like your address. To find where you are you need to know 4 things: state, city, street, house #. To know where or what state the electron is in you need to know the four quantum numbers.

Quantum #’s are like an Address. What do you need to know to find out where you live? State CityStreetHouse Principle Quantum # (n) Angular Quantum # ( l) Magnetic Quantum # (m l ) Spin Quantum # (m s )

Shapes of Atomic Orbitals s orbital P orbital d orbital

1s3s2s 2px 3pz 3d 2py 2pz 3py 3px Quantum Numbers

s and p orbital Movie

d orbital Movie

Aufbau Principle -For an atom in its ground state ( the lowest energy configuration) fill the lowest energy orbital first then go up in energy until all the electrons are used. 1s2s2p3s3p4s3d4p5s4d….. Predicting Orbital Filling Diagonal Rule 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f

Energy Levels For H atomAll other atoms 4s_4p_ _ _ 4d_ _ _ _ _4f _ _ _ _ _ _ _ 4s _ 3d _ _ _ _ _ 3p _ _ _ 3s _ 3p _ _ _ 3d _ _ _ _ _3s _ 2p _ _ _ (degenerate orbitals) 2s _ 2p _ _ _(degenerate orbitals)2s _ 1s _ Inc E

Pauli Exclusion Principle No two electrons in the same atom can have the same four quantum numbers Each electron has a unique address Designated by a set of quantum numbers (n, l,m l, m s ) So: (1,0,0, +1/2) indicates an electron in a 1s orbital While (3,1, -1, +1/2) would be a 3p electron

A.(3,2,1,+1/2) B.(3,2,-1,+1/2) C.(3,1,1,+1/2) D.(3,2,2,-1/2) E.(3,2,0,+1/2) Which of the following does not represent a 3d electrons?

What are the atomic numbers of elements whose outer most electrons are represented by 2p3 and 3p6? N= 1s 2 2s 2 2p 3 Ar=1s 2 2s 2 2p 6 3s 2 3p 6

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