What is the periodic table? A compact way of organizing the elements that contains a lot of information and allows us to make predictions about the behavior and properties of the elements. Elements

History of the Periodic Table End of the 1700’s – less than 30 elements known. Many elements were discovered during the 1800’s. Many experiments were done to determine atomic masses.

John Newlands - Octaves 1864: Newlands noticed that when the known elements were arranged by atomic masses, their properties repeated every 8 th element. Law of Octaves did not work for all known elements. Key idea was correct: Properties of elements do repeat in a periodic way.

Mendeleev & Meyer 1869: Mendeleev produced 1 st accepted periodic table. Elements ordered by increasing atomic mass into columns with similar properties. PredictedPredicted the existence & properties of undiscovered elements. Not totally correct. As more accurate determinations of atomic mass were made, several elements weren’t in the right place.

Remember 1860’s: No subatomic particles had been discovered yet. People were going by Dalton’s billiard ball model of the atom.

1913 – Henry Moseley By 1913, protons & electrons discovered. Neutrons predicted. When cathode rays hit stuff, they produce X-rays. Mosely used 30 different elements as “stoppers” Found that the greater the atomic weight of the “stopper,” the shorter the wavelength of the x-rays.

What does any good scientist do? PLOTS THE DATA! Tried correlating the wavelength of the x-ray with the atomic mass of the stopper. Not so nice. Change in much more regular than change in atomic weight.Tried correlating the wavelength of the x-ray with the atomic mass of the stopper. Not so nice. Change in much more regular than change in atomic weight. Then tried correlating the wavelenth of the x-ray with an integer, n. Got a very pretty graph.Then tried correlating the wavelenth of the x-ray with an integer, n. Got a very pretty graph.

Atomic Number Mosley interpreted the integer, n, to be the positive charge on the nucleus. Mosley suggested that the size of the nuclear charge increased by 1 with each step up the periodic table. (Before, it was organized by atomic weight.)

Moseley determined that atoms of each element contain a unique number of protons – atomic number. Moseley rearranged Mendeleev’s periodic table by atomic number instead of mass. Problems disappeared.

Periodic Law increasing atomic numberThere is a periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number.

Vocabulary of the P.T. groupsfamiliesColumns are called groups or families. 2 different notations. –1 thru 18, Arabic numerals. –Split into A & B groups. Use Roman numerals. A-Group = Columns 1,2,13-18 = representative elements B-Group = Transition metals seriesperiodsRows are called series or periods. Numbered 1 thru 7.

Classifying the Elements metals2/3 of the elements are metals. non-metals metalloidsRemaining elements are non-metals and metalloids (semi-metals). Metalloids have some properties of metals and some properties of nonmetals. staircaseKnow the “staircase” dividing line on the P.T. between metals & nonmetals. Everything to left, except H, is a metal.

Metalloids Boron, B Silicon, Si Arsenic, As Tellurium, Te Astatine, At Germanium, Ge Antimony, Sb

Names of Families Group 1 = Alkali Metals (IA) Group 2 = Alkaline Earth Metals (IIA) Group 17 = Halogens (XVIIA) Group 18 = Noble Gases (XVIIIA or O) –The noble gases are extremely unreactive. Weren’t discovered until 1890’s.

Transition Metals Elements in Columns 3 through 12 Also called the group B elements –Transition elements form brightly colored salts and brightly colored solutions. –Have multiple, positive oxidation states Actinide and Lanthanide series = inner transition elements

Calcium Metal