Atomic Theory and the Periodic Table

Reviewing the history and learning about patterns.

History - Review• Democritus – atomos• Dalton Atomic Theory– All matter is made of atoms– Atoms are indivisible (cannot be divided)– Atoms make up elements

• All atoms of an element are identical• Each element is unique (e.g. Fe is different than Pb)

– Atoms combine to form compounds• Law of Definite Composition

– Compounds have predictable proportions by mass.• Law of Multiple proportions

– More than one compound can be made from any given element.

– J.J. Thomson – cathode ray tube experiment– Ernest Rutherford – Gold foil experiment

J. J. Thomson showed this is not true, atoms contain electronsRutherford developed the idea of the nuclear atom

The development of the periodic table

Mendeleev used all of the observationsof alchemists to arrange the elements based on their chemical and physical propertiesand based on their masses.

Moseley – X-rays used to find the number of protons in an atom

Moseley discovered a few flaws in Mendeleev’s periodic table and rearrangedelements whose atomic number (the numberof protons) were unexpectedly not in the sameorder as the atomic mass (average atomic mass)

Discovery of the Noble GasesLord Rayleigh (1842-1919) and William Ramsey (1852-1916) greatly enhanced the periodic table by† discovering the "inert gases."† In 1895 Rayleigh reported the discovery of a new gaseous element named argon. This element was chemically inert and did not fit any of the known periodic groups. Ramsey followed by discovering the remainder of the inert gases and positioning them in the periodic table. So by 1900, the periodic table was taking shape with elements were arranged by atomic weight.† For example, 16g oxygen reacts with 40g calcium, 88g strontium, or 137g barium. If oxygen used as the reference, then Ca/Sr/Ba assigned atomic weights of 40, 88, and 137 respectively.

Rayleigh (physics) and Ramsey (chemistry) were awarded Nobel prizes in 1904.† The first inert gas compound was made in 1962 (xenon tetrafluoride) and numerous compounds have followed (see xenon compounds)--today the group is more appropriately called the noble gases.

http://mail.colonial.net/~cricket/FOV1-000201C0/FOV1-0004300A/?OpenItemURL=S02D2D4F1-02D2D4F1

Glen Seaborg – in the middle of the 20th century he moved the lanthanides and actinides to the bottom of the periodic table.

Nobel Prize in 1951

Metals on the left– nonmetals on the right

Metals

Periods – Horizontal Rows Groups – Vertical Columns

period

Homework: Answer questions page 10 of packet and memorize Group 1

H, Li, Na, K, Rb, Cs, Fr