DALTON AND ATOMIC THEORY Roots are in ancient philosophy; data is required to develop basic chemical laws John Dalton Elements are composed of tiny particles called atoms Atoms are indestructible; they re-arrange but never break apart Atoms of the same element are all the same Atoms of different elements are different When atoms combine to form compounds , they do so in simple, whole-numbered ratios (1:1, 1:2, 2:3 …)

ATOMIC BOOKKEEPING Atoms consist of protons, neutrons & electrons All atoms are neutral: have equal #’s of protons & electrons Mass Number = protons + neutrons Notation: AZX X = Element; A = Mass #, Z = Atomic # Number of protons in nucleus is what distinguishes one element from another

ATOMIC STRUCTURE What Do You Notice About the Structure of the Atom?

ATOMIC MASSES From Dalton All elements have constant atomic masses in compounds Ratio of elements & ratio of mass of one element to another are always the same Don’t know actual masses, but ratios are always the same So why do different forms of some elements have different masses (H, deuterium & tritium?) Isotopes Atoms of same element w/slightly different masses All elements have 2 or more isotopes What does this do to Dalton’s Theory??

ELECTROMAGNETIC SPECTRUM Protons ID atom; e’s define chemical properties Electromagnetic energy travels through matter like waves

ELECTROMAGNETIC SPECTRUM C =  x ; 3 x 108 m/sec

THE WAVE NATURE OF LIGHT Maxwell (1873) proposed that visible light was composed of electromagnetic waves These waves had 2 components that travel perpendicularly Electrical Magnetic Maxwell’s theory shows how light energy can travel through space

PLANCK & THE ELECTROMAGNETIC SPECTRUM Electromagnetic radiation is emitted in discrete packets called quanta E = h x  Each quanta or photon has the same frequency,  Energy is always emitted in fixed, whole-numbered intervals of h. Why should this be so??

EINSTEIN AND THE PHOTOELECTRIC EFFECT When metal surfaces are exposed to light of a minimum frequency (threshold frequency), electrons are emitted The energy of those electrons is not proportional to the intensity of light Photoelectric Effect: A beam of light is really a stream of particles.

SO, WHERE ARE WE? Einstein explained the photoelectric effect w/light as a particle But the particle theory of light is inconsistent with the notion of light as a wave For some experiments, light seems to behave as a particle; others as a wave. What to do??

ATOMIC LINE SPECTRA The electromagnetic spectrum is a continuous spectrum However, separate lines can be observed

ATOMIC LINE SPECTRA If you look at the gas discharge for any element, what you see is a series of sharp, distinct lines The ’s of the lines are always the same for the same element, but different for different elements

ATOMIC SPECTRA When elements are heated, they emit discrete bands of color Each element has its own distinct pattern When H is heated, it always emits the same color bands Explanation: e’s are limited only to certain energy levels

BOHR ATOM H is the simplest element and has the simplest spectrum It has lines in both the visible & UV Balmer: formula able to calculate all observed H ’s Rydberg: formula to calculate all H ’s

BOHR ATOM e’s are like planets circling the sun e’s move in fixed paths (orbits) each w/a defined energy level E = -b/n2 Ground State: Lowest energy level H absorbs energy, e’s jump from one energy level to a higher one H loses energy, e’s go from higher to lower energy level, and release energy as emitted light

BOHR ATOM

THE ANSWER: WAVE MECHANICS Wave Mechanics = Quantum Mechanics Schrodinger 1st scientist to use quantum mechanics to explain atomic structure All materials have particles & wave characteristics de Broglie  = h / m x  Energy of any object is related to its mass Mass , ; small atomic particles have short, measurable ’s

WAVE MECHANICS If you create nodes, you change the energy Waves are divided into equal segments Orbitals come in different sizes & shapes Only specific energy transitions can occur

WAVE (QUANTUM) MECHANICS Schrodinger used math to describe the motion of subatomic particles, much like Newton did for much larger objects This math specified where electrons are most likely to be found in an atom Since electron waves are 3 dimensional, one needs 3 quantum numbers to fully describe them

ORBITALS & QUANTUM NUMBERS Principal Quantum Number (n) Determines size, shape and position of shell (e wave) All e’s with same n are said to be in the same shell Angular Momentum (Secondary) Quantum Number (l) Divides shells into subshells n=1 1 subshell s n=2 2 subshells s,p n=3 3 subshells s,p,d n=4 4 subshells s,p,d,f

ORBITALS & QUANTUM NUMBERS Magnetic Quantum Number (ml) Divides subshells further into orbitals s: 1 orbital p: 3 orbitals d: 5 orbitals f: 7 orbitals Heirarchy Shells (n; 1, 2, 3, …) Subshells (l; 0 → n - 1) Orbitals (ml; 2 l + 1)

ORBITALS & QUANTUM NUMBERS

ELECTRON SPIN Any moving charged particle, such as an e, creates a magnetic field Electrons can spin clockwise & counterclockwise, creating opposing spins that allow e’s to be paired Pauli Exclusion Principle: No 2 e’s can have the same quantum numbers Spin Quantum Number: ms allows 2 e’s/orbital Paramagnetic: atom have unpaired e’s; ,magnetic Diamagnetic: no unpaired e’s; non-magnetic

ORBITAL SHAPES Now think of e’s as particles Heisenberg Uncertainty Principle: Can’t simultaneously predict position & speed of a particle Since exact e position can’t be predicted, think in terms of e clouds Also think of probability density as spots on a dart board Orbitals s p d

ORBITAL SHAPES: s ORBITALS

ORBITAL SHAPES: p ORBITALS

ORBITAL SHAPES: d ORBITALS

ORBITAL ENERGIES: ORDER OF FILLING

ELECTRONIC STRUCTURE OF ATOMS Nomenclature Orbital Diagrams Aufbau Principle: Build e structure from lowest to highest energy levels Hund’s Rule: When energy levels are equal, e’s prefer to spread out evenly Order of e Filling: 1s2, 2s2 2p6, 3s2 3p6, 4s2 3d10 4p6, 5s2 4d10 5p6

ELECTRONIC STRUCTURE OF ATOMS Groups & electronic structure Electronic structure & recurring properties Noble Gas Abbreviations: 10:[Ne], 18[Ar], 36[Kr] Valence Shell Exceptions to the Rules Cr Cu e’s prefer symmetrical distribution

ELECTRONIC STRUCTURE OF ATOMS & THE PERIODIC TABLE

ELECTRONIC STRUCTURE OF ATOMS & THE PERIODIC TABLE

ELECTRONIC STRUCTURE OF ATOMS & THE PERIODIC TABLE