Arrangements of Electrons in Atoms Chapter 4 Arrangements of Electrons in Atoms

Objectives -Define the following terms: quantum, photon, photoelectric effect, frequency, wavelength -Be able to explain the dual wave-particle nature of light -Describe Bohr’s model of an atom

Structure of the Atom -Things we know: Atoms are made up of 3 subatomic particles The nucleus holds the _________ & _________ The electrons are located ____________ We know this thanks to Thomson (electron) Rutherford (proton & nucleus) , Chadwick (neutron)

Models of Atom -Thomson’s “Plum Pudding” model: -Rutherford’s Model: Problem with model- Didn’t explain exactly where electrons could be found in the atom

Properties of Light

Electromagnetic Spectrum -the range containing all of the possible frequencies and wavelengths of electromagnetic radiation Relationship between light and electrons Research on light helped determine new model of atom Light once thought of just as wave Types of electromagnetic radiation

Electromagnetic Spectrum In order of increasing wavelength: Gamma Rays, X-Rays, Ultraviolet Rays, Visible Rays, Infrared, Microwaves, Radio Waves -Visible Light: the light WE can see

Parts of a Wave

Dual Wave/Particle Theory Waves have dual wave-particle properties. Light can act as a wave or as a particle.

Properties of Light -Wave description of Light - light exhibits wavelike behavior as it travels through space. Wavelength (λ): distance between two peaks; unit of measure – meter, cm, nanometer Frequency (f): number of waves that pass a given point in a specific time; unit of measure – Hertz (Hz) Speed of light (c ): c= λf c=3.00 X 108 m/s

Wave Description of Light Calculate the wavelength if the frequency of radiation is 5.10x1014Hz.

Properties of Light Particle description of light: light can be thought of as being composed of particles (Planck) Photon: particle of light. Has zero mass and a quantum of energy (Einstein) Quantum: minimum quantity of energy that can be lost or gained by an atom

Photoelectric effect Photoelectric effect- refers to the emission of electrons from a metal when a light of sufficient energy shines on the metal Wave theory of light couldn’t explain this effect With high energy and low wavelength electrons are ejected

Properties of Light Therefore, light has dual wave- particle properties - It behaves like a wave AND a particle

E = hf E - energy in Joules of a quantum of energy h - Planck’s constant = 6.626 x 10-34 J·s f – frequency (Hz)

Problems Find the energy in a quantum of light that has a frequency of 1.7 x 1014 Hz

Light Equations Practice 1. Find the wavelength of a photon of light with an energy of 3.26 x 10-19 J. 2. Hydrogen has a red emission line at 656.3nm. What is the energy and frequency of a photon of this light?

H atom Line-Emission Spectra When you pass a current through a gas, at low pressure, the energy of some of the gas atoms increases. Ground State - lowest energy state for an atom. Excited state - An atom that has a higher potential energy

The Two Different Sides of the Spectrum Prism Screen Slit White light source Gas discharge tube CONTINUOUS SPECTRUM FROM WHITE LIGHT SOURCE VARIOUS COLORS BLENDED TOGETHER DISCONTINUOUS SPECTRA FROM EXCITED ATOMS DISTINCT SEPARATED, ONLY A FEW COLORS

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If an electron in the n = 1 level of an H atom absorbs enough energy to move to the n = 4 level. How much energy is absorbed? n 4 If an electron in the n = 4 level of an H moves to the n = 2 level. How much energy is emitted? 3 2 Light of what wavelength is emitted in a transition from n = 4 to n = 2? Energy 1

Rydberg Formula E = 2.178x10-18(1/n2) Or if there is a change in energy levels: ΔE = 2.178x10-18(1/n2f – 1/n2i) Ex. 1 What wavelength, in nanometers, is predicted by the Rydberg equation when an electron drops from the n=6 to the n=2 state?

Rydberg Formula Ex. 2 What is the minimum wavelength of light that is capable of removing an electron from the 4th energy level of a hydrogen atom?

“Neon Lights”

Electron -Is a particle & also has wave properties -Bohr’s Model of Atom: -Electrons circle around nucleus in allowed paths (orbits) -Electrons placed in different orbits based on energy levels of the electron -One electron can not be in two orbits at once and can not be between orbits *** Bohr’s model still has shortcomings… we will discuss later)

Take Home Message -Science is CONSTANTLY changing -New research may disprove old findings -New models and thoughts may be created as a result

Review 1) Name the two properties that light has. 2) What is the type of light that we can see called? 3) Visible light is found on the _________ spectrum. 4) A particle of light that has zero mass and a quantum of energy is called a ________. 5) The distance between two peaks is called_____ 6) Name the model of an atom that said electrons circle around nucleus in allowed paths based on energy level. 7) The number of waves that pass a given point in a specific time is called ________ 8) The minimum quantity of energy that can be lost or gained by an atom is a____________. 9) The ______________ refers to the emission of electrons from a metal when a light of sufficient energy shines on the metal

Electron -Is a particle & also has wave properties -Bohr’s Model of Atom: -Electrons circle around nucleus in allowed paths (orbits) -Electrons placed in different orbits based on energy levels of the electron -One electron can not be in two orbits at once and can not be between orbits *** Bohr’s model still has shortcomings… we will discuss later)

Electron “Detection” Electrons are detected with interaction with photons Photons can knock an electron off its course Heisenberg Uncertainty Principle: It is impossible to determine simultaneously both the position and velocity of an electron or any other particle

Quantum Model - Schrödinger: wave equation Quantum Theory: Electrons can exist in atoms only at specific energy levels Wave equations only tell us probability of finding electron in certain position Currently it is believed: Electrons do not travel in orbits, but orbitals Orbital: 3-D region around nucleus. Indicates probable location of finding an electron

Section 1&2 Review What properties do light and electrons share? The emission of electrons from a metal when a light of sufficient energy shines on the metal refers to the ____________ effect. The minimum quantity of energy that can be lost or gained by an atom is called______. How is Bohr’s model different from the Quantum model of an atom? What is the principle called that says it is impossible to determine simultaneously both the position and velocity of an electron or any other particle? How is an orbital different from an orbit? Which has a higher energy level, n=1 or n=5?

Objectives -List the total number of electrons needed to fully occupy each main energy level -State the Aufbau principle, Pauli exclusion principle, and Hund’s Rule -Draw the electron configuration and orbital notation to show the location of electrons in an atom.

Electron Configuration - Electron configuration: the arrangement of electrons in an atom Rules for electron filling of orbitals: Aufbau Principle: e- will occupy the lowest energy level orbital available Pauli Exclusion Principle: no two e- in the same orbital can have the same spin Hund’s Rule: orbitals of equal energy will fill singularly before a second e- can occupy the same orbital

Electron Configuration Electron configuration shows the energy level number, the orbital sublevel, and the number of electrons in each orbital # of e- are represented by a superscript e- config for carbon: 1s22s22p2 Energy level Number of electrons Orbital sublevel

Electron Config Practice 1. Write the e-config for fluorine. 1s22s22p5 2. Write the e-config for potassium. 1s22s22p63s23p64s1 3. Write the e-config for nickel. 1s22s22p63s23p64s23d8

Review What rule says orbitals of equal energy will fill singly before a second e- can occupy the same orbital? What rule says that e- will occupy the lowest energy level orbital available? What rule says that no two e- in the same orbital can have the same spin?

Orbital Notation - Orbital notation shows e- in their orbitals First write the electron configuration Lithium 1s2 2s1 Arrows must be up and down on each line – represents electrons with opposite spins –Pauli Exclusion Principle Remember Hund’s Rule

Orbital Notation -Draw the orbital notation for aluminum. -Draw the orbital notation for phosphorus

Objectives Write the noble-gas notation of a given element Determine the element given the electron configuration or orbital notation. Determine the highest energy level that is occupied and the last orbital that is filled of a given element.

Noble Gases Gases like helium, neon, and argon Where are these on the periodic table? Group 18 The outer shell is completely filled with 8 electrons We can use their electron configuration to abbreviate the e- config. of other elements

Noble Gas Configuration The electron configuration of Manganese is: 1s22s22p63s23p64s23d5 Manganese is in period 4…. What is the noble gas in the previous period? (period 3)--- Argon Argon’s e- config. is: 1s22s22p63s23p6 We can shorten the e- config of Mn by writing: [Ar] 4s23d5

Practice - Write the Noble Gas Configuration of Na, Sr, and P

Identify the following elements 1s22s22p63s23p3 [Ar]4s1 1s22s22p1 [Ne]3s2

Review What is the last orbital occupied by an electron in the elements: He Al What is the highest energy level occupied by the following elements: Ca Be