Periodicity

PeriodicityChapter 5

Element song (Tom Lehrer),http://www.privatehand.com/flash/elements.html with Daniel Radcliffe: http://www.youtube.com/watch?v=rSAaiYKF0csNew element song: http://www.nclark.net/Meet_the_Elements.html

Other good websites for the periodic table:http://periodic.lanl.govhttp://www.periodicspiral.com/www.wou.edu/las/physci/ch412/perhist.htmwww.chemsoc.org/viselements/pages/history.htmlhttp://www.chemeddl.org/resources/ptl/http://www.ptable.com/

The History of the Development of the Periodic TableIn the 1790s Antoine Lavoisier (French Chemist) compiled a list of 23 elements. Some of these were gold, silver, carbon, oxygen.

In 1860 Stanislao Cannizzaro (Italian chemist) presented a method for accurately measuring the relative masses of atoms.

In 1864 John Newlands(English Chemist) noticed that when elements were arranged by increasing atomic mass, their properties repeated every eighth element. He called this the Law of Octaves

Lothar Meyer and Dimitri MendeleleevIn 1869 Lothar Meyer (German chemist) and Dmitri Mendeleev (Russian chemist) each demonstrated a connection between atomic mass and elemental properties.

However, Mendeleev produced the first useful and widely accepted periodic table arranged in order of increasing atomic mass.

An important facet of his table was that he left blank spaces in the table where he thought undiscovered elements should go.

Mendeleev is considered the father of the periodic table.

Properties of some elements predicted by MendeleevPredicted elementsElement & year discoveredPropertiesPredicted propertiesObserved propertiesEkaaluminumGallium1875Density of metal6.0 g/ml5.96 g/mlMelting pointLow30 COxide formulaEa2O3Ga2O3EkaboronScandium1877Density of metal3.5 g/ml3.86 g/mlOxide formulaEb2O3Sb2O3Solubility of oxideDissolves in acidDissolves in acidEkasiliconGermanium1886Melting pointHigh900CDensity of metal5.5 g/ml5.47 g/mlColor metalDark grayGrayish whiteOxide formulaEsO2GeO2Density of oxide4.7 g/ml4.70 g/mlChloride formulaEsCl4GeCl4

5Henry MoseleyIn 1913 Henry Moseley(English chemist) discovered that atoms of each element contain a unique number of protons in their nucleithe number of protons being equal to the atoms atomic number.

He proposed the Periodic Law, which states that there is a periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number.

His arrangement of elements by atomic number resulted in a clear periodic pattern of properties. This is the basis of the Modern Periodic Table which we are using now. Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers. This periodicity in properties of the elements is a function of the arrangement of electrons around the nucleus of an atom (remember that the # of electrons = the # of protons in a neutral atom)Valence electrons: The electrons available to be lost, gained, or shared in the formation of chemical compounds; i.e. the outer shell electrons.

7Periodic trendsAtomic radii: onehalf the distance between thenuclei of identical atoms that arebonded together.

8Atomic radii vs. atomic number

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Atomic Radii vs. atomic number10Cations

11Anions

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13Ionization energyThe energy required to remove one electron from a neutral atom or an element. (kJ/mol) A + energy A+ + e-

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16Electron AffinityThe energy change that occurs when an electron is acquired by a neutral atom.Most atoms RELEASE energy when they acquire an electron.A + e- A- + energySome atoms must be forced to gain an electron by the addition of energy.A + e- + energy A-

Electron affinity vs. atomic number

Electronegativitya measure of the ability ofan atom in a chemical compound to attractelectrons. Highest value isarbitrarily given toFluorine of 4.0.

20Electronegativity

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22General reactivity trends