Organizing the Elements Chapter 4 Section 2 Organizing the Elements

I. Patterns in the Elements Mendeleev’s work 1. In 1871, Russian scientist Dmitri Mendeleev noticed that some elements had similar physical and chemical properties. a. Silver and copper are both shiny metals that tarnish. b. Chlorine and fluorine are both gases that irritate the lungs and form similar compounds. 2. These properties might hold a clue to a hidden pattern.

3. Mendeleev made 63 cards, one for each element, listing their properties and atomic masses. Do Not Copy

4. He noticed that when placed in order of increasing atomic mass, a pattern appeared . If an element had similar properties to the next group , he assumed that there must be an undiscovered element and successfully predicted the missing element. a. Predicted 3 new elements which were discovered within the next 16 years. 5. Called his chart the Periodic Table.

Scandium - discovered in 1879 Gallium -discovered in 1875 Do Not Copy Scandium - discovered in 1879 Gallium -discovered in 1875 Germanium - discovered in 1886

6. In 1913, British scientist Henry Mosely discovered a way to measure the number of protons in an atom (atomic #). 7. By changing from atomic mass to atomic number, the patterns became more regular and formed the current version of the table.

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B. Organization of the Periodic Table Properties of an element can be predicted from its location on the periodic table. Periods are horizontal rows on the table. a. The properties of the elements change in a pattern.

3. Groups are vertical columns on the table which contain elements with similar properties. a. also called families. 4. Symbols for elements are always an uppercase letter first then a lower case letter if it has 2. Unnamed elements have 3 letters that tell the atomic number. 5. Symbols can be from latin names, common names, famous scientists or places. 4 Be 12 Mg 20 Ca 38 Sr 56 Ba 88 Ra

6. Reading an Elements Square Atomic Number (# of protons) Chemical Symbol Element Name Atomic Mass (Protons + Neutrons) 26 Fe Iron 55.847

Atomic Radius in periods and in groups. Do Not Copy

C. How Elements Form in Stars The sun is made up of mostly 1 element, hydrogen. The hydrogen is so hot it is in a phase of matter called a plasma (gaslike mixture of free electrons and nuclei of atoms). The pressure in a star is so high, the protons are squeezed together and collide.

4. Nuclear Fusion is when two atomic nuclei combine and “fuse” together. This releases huge amounts of energy and forms a new element.

5. Stars create heavier elements until they reach a maximum size nucleus. a. Our star will probably max out at Oxygen. b. The largest stars will max out at Iron (Fe). 6. The only way heavier elements are created is during massive explosions called supernovas.

Crab Nebula – first observed in 1045 A.D.

Cosmic Scale Models