Chapter 4 September 21, 2011

Properties of Light Light is a kind of electromagnetic radiation: form of energy that exhibits wavelike behavior as it travels through space Electromagnetic spectrum: all the forms of electromagnetic radiation

The Electromagnetic Spectrum

Properties of Light Wavelength (λ)- the distance between corresponding points on adjacent waves (units: meter, cm, nanometer) Frequency (v) the number of waves that pass a given point in a specific time (units: hertz) c= λv c= speed of light

The Photoelectric Effect http://www.youtube.com/watch?v=0qKrOF-gJZ4 End at 2:00.

The Photoelectric Effect The Particle Nature of Light Wave theory: light of any frequency would supply enough energy The experiment showed it needed a minimum frequency to eject electrons

Light has wavelike and particle-like properties Plank deduced that energy is given off in small, specific quantities called quanta Quantum: the minimum quantity of energy that can be lost or gained by an atom E=hv E= Energy (joules) of quantum radiation H= Plank’s constant- 6.626 x 10-34 v= frequency of radiation emitted Photon: particle of electromagnetic radiation having zero mass and carrying quantum of energy (Einstein)

Einstein Says… Electromagnetic radiation is absorbed by matter only in whole numbers of photons Minimum Energy= minimum frequency of photon to knock electron off metal Frequency< required energy (electron remains bound) Frequency> minimum energy (electron is ejected from metal surface)

Ground vs. Excited State Ground State: Lowest energy state of an atom Excited State: A state in which an atom has a higher potential energy than it has in its ground state Dropping from an excited state to ground state- gives off the energy gained in the form of electromagnetic radiation

Hydrogen-Atom Line Emission Spectrum Vacuum with hydrogen gas at low pressure→ pinkish glow Narrow beam of light shined through prism → specific frequencies (wavelengths) of visible light

Stumped Expected: continuous spectrum Why? Because it was predicted that Hydrogen would be excited by any amount of energy added to it Observed: specific frequencies of light

Justification Ephoton= E3-E2 1913 Niels Bohr hypothesis: electron can circle the nucleus only in an allowed path called an orbit, and when in an orbit the electron displays a fixed energy

Orbits are like a Ladder An electron can only be in one orbit or another- NOT inbetween You can only stand on one rung of a ladder or the one above it- not in the middle of the two

Energy Transitions

Section 4.2 The Quantum Model of the Atom Just like light, electrons have a wave-particle nature Heisenberg Uncertainty Principle: it is impossible to determine simultaneously both the position and velocity of an electron or any other particle Quantum Theory: describes mathematically the wave properties of electrons and other very small particles.

How do Electrons Travel? Electrons do NOT travel around the nucleus in neat orbits Electrons exist in regions called orbitals: 3 dimensional region around the nucleus that indicates the probable location of an electron Not in neat orbits!

Energy Levels As you increase in rows, an electron’s energy and distance from nucleus increases

Shape of the orbitals

Energy Levels + Orbitals 1st energy level: 1 sublevel: s orbital (only) 2nd energy level: 2 sublevels: s and p orbitals 3rd energy level: 3 sublevels: s, p, d orbitals 4th energy level: 4 sublevels: s, p, d, f orbitals 1st energy level 2ndenergy level Energy increases as you increase energy levels 3rd energy level 4th energy level

Naming energy levels + sublevel S orbital D orbitals P orbitals F orbitals

Number of Orbitals per Sublevel 1 s orbital per sublevel 3 p orbitals (x, y, z axis) in each sublevel 5 d orbitals in each sublevel 7 f orbitals in each sublevel

Spin Quantum Number A single orbital can hold a maximum of 2 electrons Let’s do some math! The s sublevel has ________ orbital per main energy level 1 2 Therefore, the s sublevel contains ______ electrons per main energy level 3 The p sublevel has ________ orbital per main energy level 6 The p sublevel has ________ electrons per main energy level The d sublevel has ________ orbital per main energy level 5 10 The d sublevel has ________ electrons per main energy level

Practice Get out your periodic table Identify the main energy levels, 1, 2, 3, 4 Identify the s, p, d blocks (where those sublevels are) What elements are in the 2 s position? What sublevel is Zinc-65 in? What main energy level and sublevel is phosphorus in? What main energy level and sublevel is calcium in?

Periodic Table

4.3 Electron Configuration Rules: Aufbau Principle: an electron occupies the lowest- energy orbital it can receive Hund’s Rule: orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron

Orbital Notation How many electrons are in Boron? What is the orbital notation Boron: Electron Configuration 1s22s22p1 Number of electrons: count the exponents Electrons=5 Orbital Notation:

A new look at things…

Inner-Shell Electrons First energy level can hold a maximum of 2 electrons 2, 3, 4 energy levels etc. can hold up to 8 electrons

Valence Electrons Valence Electrons: electrons in the outermost shell that can participate in the formation of chemical bonds with other atoms To figure out valence electrons: Group 1= 1 valence electron Group 2=2 valence electrons Group 13= 3 valence electrons Group 14=4 valence electrons Group 15= 5 valence electrons Group 16= 6 valence electrons Group 17= 7 valence electrons Group 18= 8 valence electrons P block Group 13-10= valence electrons

Practice Valence Electrons How many valence electrons are in each of the following elements? Lithium Carbon Helium Chlorine Tellerium (Te) Calcium Nickel 1 4 2 7 6 2 2

Lewis Dot Structures

Practice Lewis Structures Lithium Carbon Helium Chlorine Tellerium (Te) Calcium Nickel

Electron Configuration Notation Helium: Lithium: Boron: Carbon: Neon: Sodium: 1s22s22p2 1s22s22p6 1s22s22p63s1

Noble Gas Configuration Sodium: OR 1s22s22p63s1 [Ne]3s1 Noble Gas Configuration