The Periodic Table SC1. Obtain, evaluate, and communicate information about the use of the modern atomic theory and periodic law to explain the characteristics of atoms and elements. f. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms (i.e. including atomic radii, ionization energy, and electronegativity). g. Develop and use models, including electron configuration of atoms and ions, to predict an element’s chemical properties.

Ancient Times 330 BC – Aristotle proposed that everything was made of a mixture of one or more roots, later called elements by Plato: earth, fire, water, and air 1649 – Brand discovered phosphorus while trying to discover the Philosopher’s Stone 1789 – de Lavoisier wrote the first textbook on chemistry in which he listed several “simple substances” which he claimed could not be broken down any further. He also classified substances into metals and nonmetals.

Dobereiner 1829 – Developed the Law of Triads, observing that if groups of chemically similar elements were arranged in increasing order of their atomic weights, they formed well marked groups of three called triads

De Chancourtois 1862 – The first person to recognize the repeating patterns of the elements when arranged by their atomic weights

Newlands 1864 – Noted that many pairs of similar elements existed, which differed by some multiple of eight in mass number – termed the Law of Octaves. He was the first to assign atomic numbers to elements and contributed the word “periodic” in chemistry.

Mendeleev 1869 – Published the first table of the elements organized by increasing atomic mass.

Elements known in Mendeleev’s time

Mendeleev stated that... If the elements are arranged according to their atomic mass, they exhibit apparent periodicity of properties Elements which are chemically similar have atomic weights that are similar or increase regularly The arrangement of the elements corresponds to their valencies and to their distinctive chemical properties

Mendeleev stated that... If the atomic weight of an element may sometimes be amended by a knowledge of those contiguous to it (he corrected the atomic masses of Be, In, and U) One should expect the discovery of many yet unknown elements Certain characteristic properties of elements can be foretold from their atomic masses

After the discovery of these unknown elements between 1874 and 1885, and the fact that Mendeleev’s predictions for Sc, Ga, and Ge were amazingly close to the actual values, his table was generally accepted.

However, in spite of Mendeleev’s great achievement, problems arose when new elements were discovered and more accurate atomic weights determined. By looking at our modern periodic table, can you identify what problems might have caused chemists a headache? Ar and K Co and Ni Te and I Th and Pa

Moseley 1914 – Through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number. *“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.”

Seaborg 1944 – After co-discovering 10 new elements, he moved 14 elements out of the main body of the periodic table to their current location below the lanthanide series. These became known as the actinide series.

Seaborg He is the only person to have an element named after him while still alive. "This is the greatest honor ever bestowed upon me - even better, I think, than winning the Nobel Prize."

Periodic Table Geography

The horizontal rows of the periodic table are called PERIODS

The elements in any group of the periodic table have similar physical and chemical properties! The vertical columns of the periodic table are called GROUPS, or FAMILIES

Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.

Alkali Metals Soft, silvery, highly reactive metals Second most reactive group Only found in combined state in nature Form alkaline/basic compounds with water Alkali Metals

Alkaline Earth Metals Harder, silvery, less reactive metals Readily form oxides, which produce alkaline compounds in water Alkaline Earth Metals

Transition Metals Most “metal-like” High hardness and density Very conductive Transition Metals

Inner Transition Metals Generally, lanthanides are naturally occurring. All actinides are radioactive and most are synthetic. Inner Transition Metals

Halogens Nonmetals; all 3 states represented Most reactive group Only found in combined state in nature Toxic to living organisms Halogens

Noble (Inert) Gases Virtually unreactive gases Most stable elements on the PT Noble (Inert) Gases

Properties of Metals Metals... are solid (except Hg, a liquid) are good conductors of heat and electricity are lustrous (shiny) are ductile (can be stretched into thin wires) are malleable (can be pounded into thin sheets) have higher density have higher MP/BP are electropositive

Properties of Nonmetals are poor conductors of heat and electricity are brittle, if solid are not lustrous, ductile, or malleable, if solid are solid, liquid or gas (most) are electropositive have lower density have lower MP/BP Sulfur

Properties of Metalloids have physical properties of metals and chemical properties of nonmetals are solids that can be shiny or dull conduct heat and electricity better than non- metals but not as well as metals (semi-conductors) can be ductile and malleable or brittle Silicon

The periodic table is the most important tool in the chemist’s toolbox!