Electrons in Atoms

In this chapter… Scientists pursue an understanding of how electrons are arranged within atoms Electron arrangement plays a role in chemical behavior

Early 1900’s- scientists observed that certain elements emit visible light when heated in a flame

Wave Nature of Light Electromagnetic Radiation- form of energy that exhibits wavelike behavior as it travels through space

Vocabulary to know.. Wavelength- shortest distance between equivalent points on a wave Symbol- λ Unit- meters, centimeters, or nanometers (1 nm= 1x10-9m) Frequency- the number of waves that pass a given point per second Symbol- ν Unit- Hertz (SI Unit)= (1/s)= (s-1) cycle per second

How are they related? C= λν c= 3.00x108 m/s ALL electromagnetic waves, including visible light, travel at the speed of light c= 3.00x108 m/s Wavelength must be in meters! C= λν

Electromagnetic Spectrum Encompasses all forms of electromagnetic radiation The only differences in the types of radiation being their wavelengths and frequencies

ROYGBIV

As the wavelength increases, the frequency decreases. As the frequency increases, the energy increases.

Calculations  1. Microwaves are used to transmit information. What is the wavelength of a microwave having a frequency of 3.44 x109 Hz? C= λν C= 3.00x108 m/s ν = 3.44 x109 Hz λ = ???

3.00x108 = λ(3.44x109 Hz) λ= 8.72 x10-2 m

2. Yellow light has a wavelength of 589 nm. What is the frequency. 5 2. Yellow light has a wavelength of 589 nm. What is the frequency? 5.09x1014 Hz

Particle Nature of Light (Honors) Quantum Concept Explained why colors of heated matter correspond to different frequencies and wavelengths Max Plank- “matter can gain or lose only in small, specific amounts called quanta” Quantum- the minimum amount of energy that can be gained or lost by an atom

Energy of a quantum is related to the frequency of the emitted radiation by the equation Equantum= hv E= energy h = Plank’s Constant (6.63x10-34Js) v= frequency Joule (J)= SI unit for energy

Photon- a particle of EM radiation with no mass that carries a quantum of energy Ephoton= hv

Example Calculate the quantum of energy that an object can absorb from light with a wavelength of 477 nm. 4.17x10-19 J

Atomic Emission Spectra Set of frequencies of the electromagnetic waves emitted by atoms of the element Example- The light of neon sign is produced by passing electricity through a tube filled with neon gas. Neon atoms release energy by emitting light.

An atomic emission spectrum is characteristic of the element being examined and can be used to identify that element

Bohr Model of the Atom Proposed that the hydrogen atom has only certain allowable energy states Ground State- lowest energy state of an atom Excited State- higher energy state

An electron must absorb energy to move from a lower energy level to a higher level. Electrons do not stay in the excited state. When the electrons return to lower energy levels, energy is emitted.

The Heisenburg uncertainty principle - states that it is impossible to know precisely both the velocity and position of a particle at the same time

The Bohr Model Using the Bohr Model from your packet, what is the wavelength of energy that is emitted when an electron falls from n= 6 to n=3? wavelength = 1094 nm

B) What is the frequency of this radiation. 2 B) What is the frequency of this radiation? 2.75x1014 Hz C) What is the energy of a photon of this radiation? (Honors) 1.82x10-19 J

Atomic Orbital- a 3D region around the nucleus describing the electron’s probable location

Atomic Orbitals Energy Levels (n)- the major energy levels of an atom Ex: n = 1 energy level closest to the nucleus Energy level → sublevel → orbital Every orbital can hold up to 2 e-

Sublevels are represented by the letters s, p, d, f lowest energy highest energy

First 4 Principal Energy Levels Sublevel Orbital Number of Electrons 1 s 1 2 s 1 2 2 p 3 6 (8 total e-) s 1 2 p 3 6 3 d 5 10 (18 total e-) s 1 2 p 3 6 4 d 5 10 f 7 14 (32 total e-) 2n2 = maximum # of electrons in energy level

Electron Arrangement in Atoms Electron Configurations- the arrangement of electrons in an atom

Aufbau Principle : Electrons enter orbitals from lowest to highest energy

Writing Electron Configurations H (1e-) 1s1 energy level sublevel # e-

Writing Electron Configurations He (2e-) 1s2 Li (3e-) 1s2 2s1 Be (4e-) 1s22s2

Writing Electron Configurations B (5e-) 1s22s22p1 C (6e-) 1s22s22p2 Ne (10e-) 1s22s22p6

Writing Electron Configurations Na (11e-) 1s22s22p63s1 Si (14e-) 1s22s22p63s23p2 Cl (17e-) 1s22s22p63s23p5

s p d f

Noble Gas Configuration Used to shorten electron configurations Sodium: #11- instead of 1s22s22p63s1 can be shortened to [Ne] 3s1

Examples Write the shorthand electron configuration of Mn. [Ar]4s23d5 [Xe]6s24f145d106p5

Big Bang – Sheldon Video

Valence Electrons (V.E.) Electrons in the atom’s outermost energy level Determine the chemical properties of an element V.E. are used in forming chemical bonds

Examples Write the electron configuration and give the number of valence e-. Mg 2 valence e- Br 7 valence e- V

Exceptions 1. Cu not [Ar]4s23d9 but [Ar]4s13d10 2. Ag [Kr]5s14d10 3.  Au [Xe]6s14f145d10

Exceptions 4. Cr [Ar]4s13d5 5. Mo [Kr]5s14d5

Ions Cations (+ ions) –remove e- Anions (- ions) - add e- O: 1s22s22p4 O2- is isoelectronic with ________. Ne

Examples Write the electron configuration for: P3-: 1s22s22p63s23p6 Al3+:  1s22s22p6 Ba2+: [Xe]

Examples Pb: [Xe]6s24f145d106p2 Pb2+: [Xe]6s24f145d10 Pb4+: [Xe]4f145d10

Transition Metals Fe:  [Ar]4s23d6 Fe2+:  [Ar]3d6 Fe3+: [Ar]3d5

Transition Metals Mn: [Ar]4s23d5 Mn2+: [Ar]3d5 Mn4+: [Ar]3d3 What is the highest possible charge for Mn? +7

Excited state: e- jumps to higher energy level Ex: 1s22s22p63p6 Ground state: normal e- configuration (lowest energy) Ex: 1s22s22p63s23p1 Blue Book: pg 358 # 37-39

Orbital Diagrams Use arrows to represent electrons Use lines to represent orbitals Every orbital can hold up to 2 e-

s ____   p ____ ____ ____ d ____ ____ ____ ____ ____ Lines represent orbitals.

Orbital Diagram Draw the orbital diagram for carbon

Hund’s Rule- atoms contain the maximum number of unpaired electrons

p s