Page 1 Atomic Structure and the Periodic Table long suspected Electricity and Chemistry related Quantum (wave) Mechanics - provides basis electron (a particle) has a wavelength (De Broglie) allowed stated fundamental (resonance) frequencies determines Elements and their Periodic Properties Robert Boyle (1627-1691) 1691) chemist provided definition ELEMENT - pure substance that can not be decomposed into simpler substances by ordinary chemical or physical means. Symbols for Elements Jöns Jakob Berzelius (1779-1848) 1848) Stockholm capitalize 1st letter of name H Hydrogen or add lowercase 2nd letter He Helium or use Latin name Pb Lead (Plumbum) discoverer gets to name new elements see tables 13-1 1 through 13-5 The Periodic Table Meyer (1830-1895) 1895) German (L) Mendeleev (1834-1907) 1907) Russian (R) chemists arrange elements by mass from light to heavy Properties density, solubility, melting & boiling points, ionization energies, hardness recur at definite intervals Periods
Page 2 Mendeleev's 1872 table left blanks where sequence didn't match predicted new elements Robert Moseley (1887-1913) 1913) English physicist worked with Rutherford studied X-ray emission Atomic Number more fundamental than mass Moseley's Law properties of the elements are a periodic function of their atomic number. Periodic Table modern relates chemical and physical properties of Groups of elements Element ATOM - smallest unit of an element Nucleus - positively charged "core" size ~ -14 m held together by Strong Force Nucleons of mass 1.66-27 -19 C Protons, p with + charge 1.6 Neutrons, n no charge - m -19 C Electron cloud size ~ 1-3 1 electron charge -1.6 1.6 mass 9.1-31 Each element has a unique ATOMIC NUMBER, Z = number of protons in nucleus = number of electrons in neutral atom ISOTOPE of an element iso=same topos=place has different number of neutrons
Page 3 has no effect on chemical or electrical properties! MASS NUMBER, A = n + p = no. of protons + no. of neutrons used to specify isotopes Neon 20: p + n Neon 21: p + 11 n Neon 22: p + 12 n amu - Atomic Mass Unit mass of one atom relative to the standard CARBON-12 = 12.00000 amu measured with Mass Spectrometer Particle Charge Mass (amu) Relative Mass electron -1 0.00055 1/1837 proton +1 1.00728 1 neutron 0 1.00866 1 Carbon-12 has 6 protons and 6 neutrons, but 6 1.00728 + 6 1.00866 = 12.09564 amu > 12.00000 amu A Carbon-12 nucleus has less mass than its parts. What happened to the missing mass? E = mc 2 energy mass STABLE NUCLEUS - lower mass (energy) than sum of parts must add energy to break apart UNSTABLE NUCLEUS - can gain energy by breaking apart radioactive decay a neutron has less mass than proton + electron a free neutron decays to proton + electron with a half-life life of.3 min a bound neutron in a nucleus is stable ATOMIC MASS - weighted average of natural abundance given as amu in Periodic Table isotope amu fraction contribution Neon-20 19.99 0.9092 18.18 Neon-21 20.99 0.0026 0.05 Neon-22 21.99 0.0822 1.95 1.0000 20.18 amu Quantum (wave) Mechanics successfully explained Periodic Table in terms of Electronic Structure
Page 4 how electrons arranged and interact outside nucleus electron wavelength fundamental (resonant) frequencies certain allowed energies ENERGY LEVELS Details from Schrödinger Equation 2 Ψ = dψ/dt Details from like Maxwell's equations for electromagnetic waves Ψ = wavefunction, Ψ 2 = probability of finding particle Heisenberg Uncertainty Principle x p p ~ h/2π if we know momentum p (energy) exactly we can not know the exact position x "electron cloud" Pauli Exclusion Principle no 2 electrons can have identical quantum numbers Solutions labeled by 4 Quantum Numbers n principal quantum number main energy level l angular momentum sublevel l = 0 up to n-1 n orbitals: s, p, d, f,... m magnetic quantum number m = -l,,..., 0,..., l for l =1, m = -1, 0, 1 p x p y p z l and m give shape and orientation of electron cloud s spin quantum number 2 possible values up or down to find electronic structure fill quantum states starting with lowest possible energy: 1s 2 2s 2 2p 6 3s 2 3p 6
Page 5 4s 2 3d 5s 2 4d 6s 2 4f... 3d 4p 6 4d 5p 6 4f 14 5d 6p 5d 6p 6 example: 11 Na has structure 1s2 2s 2 2p 6 3s 1 = [Ne] 3s 1 (2+2+6+1 = 11) OUTER ELECTRONS determine all chemical and most physical properties via orbital shapes filled outer shell Inert or Noble gasses chemical bonding tries to complete outer shell Elements in same column (Group) have same outer shell and similar chemical properties.