2 OBJECTIVESExplain how atomic emission spectra can be used to identify elementsDescribe Bohr’s model of the atom.Describe the Quantum Mechanical model of the atomWrite elements’ electron configurations.
4 ATOMIC EMISSION SPECTRA When an element is heated, its atoms absorb energy and become excitedTo become stable again, these excited and unstable atoms then release the energy as lightIf this light is passed through a prism the element’s atomic emission spectrum is produced
7 ATOMIC EMISSION SPECTRA An element’s atomic emission spectrum is the set of wavelengths (colors) of light given off when atoms of that element are excited (e.g. heated)Each element’s emission spectrum is unique and can be used to identify the elementIt is the element’s “fingerprint”
10 HOW DO WE KNOW WHAT THE STARS ARE MADE OF? Scientist analyze the light from a star using spectroscopes (similar to powerful prisms)Match the frequencies of light to the known spectra of the elementsStars are made of the same stuff as the rest of the Universe: 73% hydrogen, 25% helium, and the last 2% is all the other elements
11 LIGHT Visible light is a type of electromagnetic radiation All other electromagnetic radiation is invisibleElectromagnetic (EM) radiation is energy that travels through space in the form of electromagnetic wavesThe electromagnetic spectrum encompasses all forms of electromagnetic radiations
14 BOHR’S MODEL OF THE ATOM Bohr studied the emission spectrum of hydrogen and developed his model of the atomThe Bohr model describes the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around it
15 THE BOHR MODEL OF THE ATOM Each orbit or “ring” has a distinct energy levels or quantum number (n)the bigger the number the higher the energyElectrons in smaller orbits closer to the nucleus have less energy than electrons found in larger orbits farther from the nucleus
16 BOHR’S ATOM CONTINUEDThe lowest energy state of an atom is its ground stateWhen an atom gains energy (through heating for example) it is in an excited statein an excited state the electron absorbs the energy & jumps to higher energy levelwhen it falls back down to its ground state it releases excess energy in the form of light
17 BOHR MODEL CONTINUEDBecause electrons jump between orbitals that have specific energy levels only certain colors can be given offThis is how Bohr explained hydrogen’s emission spectrumTransitioncolor of light emittedn = 3 to n = 2redn = 4 to n = 2blue-greenn = 5 to n = 2bluen = 6 to n = 2violet
19 Wait!Bohr’s model explained the emission spectrum of Hydrogen, but it did not explain the emissions of any other element!
20 THE QUANTUM MECHANICAL MODEL OF THE ATOM Electrons behave like wavesIt is impossible to know the exact location or the velocity of an electron in an atom(they don’t travel in circular orbits around the nucleus)Although it’s impossible to describe the exact location or describe how they are moving, the model describe the probability that electrons will be found in certain locations around the nucleus
21 ATOMIC ORBITALSAn atomic orbital is a three-dimensional pocket of space around the nucleus that the electron is most likely to be foundAn electron has a 90% chance of being found within that spaceThat is the best we can do!
23 ORGANIZATION OF ATOMIC ORBITALS 1. Principal energy level (n)2. Energy Sublevel3. Orbitalsvalue:n = 1-7s, p. d, f1, 3, 5, 7description:-(n) indicates relative size and energy of orbital-As (n) increases so do energy and size-sublevels are labeled according to shape:s: sphericalp: dumbbell d/f: varied-each sublevel has a certain number of orbitals:s = 1p =3d =5f = 7-each orbital can hold two electrons
26 ELECTRON CONFIGURATION An atoms electron configuration is the way an atom’s electrons are distributed among the orbitals of an atomThe most state stable electron configuration is an atom’s ground stateGround state: all electrons are in the lowest possible energy stateElectron configuration represented by writing symbol for the orbital and a superscript to indicate the number of electrons in the orbital Li: 1s2 2s1
28 Each orbital can hold two electrons 4pEnergy3d4s3p3sHHydrogen11.008HeHelium24.003LiLithium36.941CCarbon612.01BBoron510.81BeBeryllium49.012OOxygen816.00NeNeon1020.18NNitrogen714.01FFluorine919.002p2s1s
29 The Pauli Exclusion Principle The two electrons in an orbital must spin in opposite directions 1s2s2p4s3d3s3p
30 HUND’S RULE Negatively charged electrons repel each other, so: Electrons won’t pair up unless they have toOnce there is one electron in every orbital…the pairing will begin!2s1s2p1.Add an electron:2s1s2p2.Add an electron:2s1s2p3.Add an electron:2s1s2p4.
31 DRAW THE ORBITAL DIAGRAM AND WRITE THE ELECTRON CONFIGURATION FOR: CarbonHeliumPotassium
32 ELECTRON CONFIGURATION The periodic table can be divided into four distinct blocks based on valence electron configurationelectron configuration explain the recurrence of physical and chemical properties
33 SHORTHAND (NOBLE GAS) NOTATION Shows electron filling starting from previous noble gas:Na: 1s22s22p63s1Noble gas configuration: [Ne]3s1