CHEM 1A03: Unit 4 - Periodic Trends

Dalton

first list of elements from 1803 consisted of 5 elements. His
second list in 1808 featured 20 elements with their atomic weights.

Berzelius

accurately measures the elements atomic weight, and publishes his list in 1828. Introduced chemical symbols.

tried to find order in the chemical properties of the elements, grouping chemically similar elements in triads

Newlands

ordered 56 elements by atmoic weights and found recurring properties every eight elements known as the law of octaves.

Dmitri Mendeleev

Dmitri Mendeleev (1834 – 1907) formulated the

Periodic Law and the Periodic Table of Elements

which predicted elements yet to be discovered

How did he organize the table?

Dmitri Mendeleev’s periodic table from 1871. Mendeleev organized the known elements into eight groups, in order of increasing mass. He left gaps for undiscovered elements and predicted their properties

n, radius

Shielding, and zeff

Nuclear charge and shielding

• For one electron species, the greater the nuclear charge (z), the lower the energy of the electrons

• For multielectron species, electrons repulsions destabilize the electrons (shielding-s) & increases their potential energy.

Core electrons and orbital penetration

• Inner electrons shield outer electrons from the full attractive charge from the nucleus (effective nuclear charge) Zeff = Z – S

• Orbitals that penetrate closer to the nucleus experience a higher effective nuclear charge

and reduced shielding (s > p > d > f)

Everybody wants to be a noble gas

• elements will lose or gain electrons in order to be isoelectronic with noble gases

• 8 valence electrons make them stable