Atomic Structure and the Periodic TableAtomic Structure ...

[Pages:5]Periodic Table Prof. Voss

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) chemist provided definition

ELEMENT - pure substance that can not be decomposed into simpler substances by ordinary chemical or physical means.

Symbols for Elements

J?ns Jakob Berzelius (1779-1848) 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 through 13-5

The Periodic Table

Meyer (1830-1895) German (L)

Mendeleev (1834-1907) 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

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Periodic Table Prof. Voss

Mendeleev's 1872 table left blanks where sequence didn't match

predicted new elements

Robert Moseley (1887-1913) 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 ~10?-14m held together by Strong Force Nucleons of mass 1.66?10-27 kg Protons, p with + charge 1.6?10-19 C Neutrons, n no charge Electron cloud size ~ 1-3?10-10 m electron charge -1.6?10-19 C mass 9.1?10-31 kg

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

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Periodic Table Prof. Voss

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: 10 p + 10 n Neon 21: 10 p + 11 n Neon 22: 10 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 = mc2 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 of 10.3 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 Neon-20 19.99 0.9092 Neon-21 20.99 0.0026 Neon-22 21.99 0.0822

1.0000

contribution 18.18 0.05 1.95 20.18 amu

Quantum (wave) Mechanics successfully explained Periodic Table in terms of

Electronic Structure

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Periodic Table Prof. Voss

how electrons arranged and interact outside nucleus electron wavelength

fundamental (resonant) frequencies certain allowed energies ENERGY LEVELS

Details from Schr?dinger Equation 2 = d/dt

like Maxwell's equations for electromagnetic waves = wavefunction, ||2 = probability of finding particle

Heisenberg Uncertainty Principle xp ~ h/2

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 orbitals: s, p, d, f, ...

m magnetic quantum number m = -l, ..., 0, ..., l for l =1, m = -1, 0 , 1 px py pz

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: 1s2 2s2 2p6 3s2 3p6

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Periodic Table Prof. Voss

4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6

...

example: 11Na has structure 1s2 2s2 2p6 3s1 = [Ne] 3s1 (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.

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