Properties of Light Electromagenetic Spectrum

Electromagnetic Spectrum Types of electromagnetic radiation -the range containing all of the possible frequencies and wavelengths 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 the light WE can see

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 10 8 m/s

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

E = hf E - energy in Joules of a quantum of energy E - energy in Joules of a quantum of energy h - Planck’s constant = x J·s h - Planck’s constant = x J·s f - frequency f - frequency

Problems 1. Calculate the wavelength if the frequency of radiation is 5.10 x Hz.

Problems 2. Find the energy in a quantum of light that has a frequency of 1.7 x Hz

Problems 3. Find the wavelength of a photon of light with an energy of 3.26 x J.

Violet nm Indigo nm Blue nm Green nm Yellow nm Orange nm Red nm Find the color of a photon of light if it is known to have an energy of 4.75x J.

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

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. 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 electron. Ground State - lowest energy state for an electron. Excited state - An electron that has a higher potential energy Excited state - An electron that has a higher potential energy When an electron drops down from an excited state to its ground state, light of a certain wavelength is emitted When an electron drops down from an excited state to its ground state, light of a certain wavelength is emitted

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

2

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

“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 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 e lectrons 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

Quantum Numbers

Review 1) Name the two properties that light has. 2) A particle of light that has zero mass and a quantum of energy is called a ________. 3) The minimum quantity of energy that can be lost or gained by an atom is a____________. 4) Name the model of an atom that said electrons circle around nucleus in allowed paths based on energy level.

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 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)

Electrons as Waves Early 20 th century: -De Broglie: believed electrons have dual wave- particle properties -Scientists demonstrated that electrons could be bent or diffracted -Diffraction: bending of a wave as it passes by the edge of an object

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

Quantum numbers - Quantum numbers: specify the properties of atomic orbitals and the electrons in orbitals - Four different Quantum Numbers - Principal Quantum Number - Angular Momentum Quantum Number - Magnetic Quantum Number - Spin Quantum Number

Principal Quantum Number - Symbol: n - Main energy level occupied by the electron - Whole numbers (1, 2, 3, …) - n=1 : Lowest energy level (closest to nucleus) - Gives an indication of the size of the orbital

Angular Momentum Quantum Number - Symbol: l - Indicates the shape (sublevels) of the orbital - l= zero, one, two,…. (n-1) - Shapes s: spherical, p: dumbbell, d, f Value of l: 0123 Letter used:spdf

Magnetic Quantum Number - Symbol: m - Indicates the orientation of an orbital in space - s orbital has 1 orientation, p orbital has 3, d orbital has 5, f has 7

Spin Quantum Number - Indicates the spin of an electron in an orbital - A single orbital can hold a maximum of 2 electrons with OPPOSITE spins - Practice: - How many orbitals are in n=3? - How many electrons are in n=3?

Electron Configuration

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

The Order of Electron Filling 7s7p7d7f 6s6p6d6f 5s5p5d5f 4s4p4d4f 3s3p3d 2s2p 1s Remember the Aufbau Principle

The Order of Electron Filling 7s7p7d7f 6s6p6d6f 5s5p5d5f 4s4p4d4f 3s3p3d 2s2p 1s Remember the Aufbau Principle

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 - 1s 2 2s 2 2p 2 - Write the e-config for fluorine. - Write the e-config for silver.

Orbital Notation Orbital notation for Carbon

Orbital Notation - Orbital notation shows e- in their orbitals - First write the electron configuration __________ T his is the orbital notation for Lithium 1s 2s 1s 2s Remember the Pauli Exclusion Principle & Hund’s Rule

Orbital Notation -Draw the orbital notation for fluorine -Draw the orbital notation for nitrogen

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

Chapter 4-3

The Order of Electron Filling 7s7p7d7f 6s6p6d6f 5s5p5d5f 4s4p4d4f 3s3p3d 2s2p 1s Remember the Aufbau Principle

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 (main energy level) is completely filled with 8 electrons - We can use their electron configuration to help abbreviate the e- config. of other elements

Noble Gas Configuration - The electron configuration of Manganese is: - 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 - Manganese is in period 4…. Look at the noble gas in the previous period (period 3)--- Argon - Argon’s e- config. is: - 1s 2 2s 2 2p 6 3s 2 3p 6 - We can shorten the e- config of Mn by writing: - [Ar] 4s 2 3d 5

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

Short cuts with the Periodic Table Look at the period number, group number, and block Look at the period number, group number, and block

Identify the following elements A) 1s 2 2s 2 2p 6 3s 2 3p 3 B) [Ar]4s 1 C) 1s 2 2s 2 2p 1 D) [Ne]3s 2

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