Arrangement of Electrons in Atoms

Chapter 4

The New Atomic Model Investigations relationship between light

and atom’s electrons How are electrons arranged? Why don’t

they fall into the nucleus?

Light a wave or particle? Wave Description:

Electromagnetic Radiation: energy that acts like a wave in space

All forms create Electromagnetic Spectrum

Electromagnetic Spectrum

Electromagnetic Spectrum All forms move at speed of light, c,

3.00x108 m/s Forms identified by:

wavelength, , the distance b/ corresponding points on adjacent waves. Units: nm, cm, or m

Frequency, , # of waves that pass a given point in a specific time, 1 sec. Unit: 1/s = Hertz, Hz

Wavelength and Frequency

Wavelength and Frequency

c =

Inverse proportion equation!!

speed of light, m/s

wavelength, m

Frequency, 1/s

Calculation Calculate the wavelength of a radio wave

with a frequency of 102.7 x 106s-1

Determine the frequency of light whose wavelength is 5.267 nm.

Particle Nature of Light

Photoelectric Effect: emission of electrons from a metal when light shines on the metal

Photoelectric Effect Light had to be certain frequency to knock

e- loose Wave theory any frequency should

work (just might take a while) Light must also be a particle! Max Planck(1900) explanation: objects

emit energy in small packets called quanta Video - 16

Max Planck Quantum of energy is the smallest amount

of energy that can be lost or gained by an atom

E = hEnergy of quantum, in joules, J

Planck’s constant,

6.626x10-34 Js

Frequency, s-1

Energy Calculation What is the energy of green light, with a

wavelength of 500. nm?

Albert Einstein Light is both wave and particle! Particle of light = photon, having zero

mass and a quantum of energy Photons hit metal and knock e- out, but

photon has to have enough energy

H-atom Emission Spectrum Pass a current through gas at low pressure

it excites the atoms Ground state: lowest energy state of an

atom Excited state: atom has higher potential

energy than it has in ground state

H – Atom Spectrum When atom jumps from excited state to

ground state it gives off energy LIGHT!

Ephoton = E2 – E1 = hv

E2

E1

Bohr Model of H-atom

H-atom Line Emission Spectrum

Element Emission SpectrasHelium – 23 lines

Neon – 75 lines

Argon - 159 lines

Xenon – 139 lines

Mercury – 40 lines

H-atom Line Emission Spectrum More lines in UV (Lyman series) and

IR(Paschen series) Why did H-atom only emit certain colors

of light? Explanation led to new atomic theory

Quantum Theory

Bohr Model of H-atom 1913 – Niels Bohr e- circles nucleus in certain paths, orbits or

atomic energy levels e- is higher in energy the farther away from

nucleus e- cannot be between orbits Video - 23

Bohr Model of H-atom

Bohr Model of H-atom From wavelengths of emission spectrum

Bohr calculated energy levels of H-atom Model worked ONLY for H-atom

Quantum Model of Atom Can e- behave as a wave?

Yes! To find e- use a photon, but photon will

knock the e- off course Heisenberg Uncertainty Principle:

impossible to determine position and velocity of a particle at the same time.

Schrödinger Wave Equation 1926 – developed equation and only e-

waves of certain frequencies were solutions Quantization of e- probability of finding

e- in atom No neat orbits probability clouds or

orbitals

Electron Configurations

Atomic Orbitals Def: 3-D region around nucleus that

indicates the probable location of an electron

Energy levels or shells: Numbered 1-7 Smaller number = closer to nucleus, lower

energy

Sublevels Each shell has sublevels s

1 – s orbital p

3 – p orbitals d

5 – d orbitals f

7 – f orbitals

Shells and Sublevels Shells and sublevels together: 1s 2s, 2p 3s, 3p, 3d 4s, 4p, 4d, 4f, etc. s is the lowest energy and f is the highest

Orbitals

Each orbital in a sublevel can hold a maximum of 2 e-

1 – s 2 e- max. 3 – p orbitals 6 e- max. 5 – d orbitals 10 e- max. 7 – f orbitals 14 e- max.

Electron Configurations Arrangement of e- in atom Orbital Notation: H has 1e- Rules:

1. Aufbau Principle: electron occupies lowest energy level that can receive it

Electron Configurations2. Pauli Exclusion Principle: no two e- in

an sublevel orbital can have the same spin3. Hund’s Rule: orbitals of equal energy are

occupied by one e- before pairing up e-. All single occupied orbitals must have same spin.

He – 2e-

Energy of sublevels

Electron Configurations N S Ti I

Electron Configuration Notation B Ni Hg

Noble Gas Notation Use noble gas from previous row

Al Pb

Special Cases d sublevel more stable with half-filled or

completely filled sublevel Cr Cu