Why is the Periodic Table important to me? • The periodic table is the most useful tool to a chemist. • It organizes lots of information about all the known elements. • You get to use it on every test.
Pre-Periodic Table Chemistry … • …was a mess!!! • No organization of elements. • Imagine going to a grocery store with no organization!! • Difficult to find what you need. • Chemistry didn’t make sense.
During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table.
How did chemists begin to organize the known elements? As the number of elements increased, chemists inevitably began to find patterns in their properties. Chemists used the properties of elements to sort them into groups Ex. Chlorine, bromine, and iodine have very similar chemical properties.
Model of Triads In 1817, Johann Dobereinerclassified some elements into groups of three, which he called triads.The elements in a triad had similar chemical and physical properties. 1780 - 1849
In 1865, John Newlands suggested that elements be arranged in “octaves” because he noticed when he arranged the elements in order of increasing atomic mass certain properties repeated every 8th element. Law of Octaves 1838 - 1898
Lightest to heaviest. ABCDEFGABCDEFGABCDEFG Li BeBCNOF NaMgAlSiPSCl K Ca??AsSeBr Li BeBCNOF NaMgAlSiPSCl K Ca??AsSeBr He called this the “Law of Octaves” because of its similarity to musical octaves
Law of Octaves John Newlands Newlands' claim to see a repeating pattern was met with savage ridicule on its announcement. His classification of the elements, he was told, was as arbitrary as putting them in alphabetical order and his paper was rejected for publication by the Chemical Society.
In 1869 Dmitri Mendeleev published a table of the elements organized by increasing atomic mass.He was trying to organize elements so his students could learn them more easily! The Modern Periodic Table 1834 - 1907
A.MendeleevandChemical Periodicity • Mendeleev placed known information of elements on cards (atomic mass, density, etc…). He arranged them in order of increasing atomic masses, certain similarities in their chemical properties appeared at regular intervals. Such a repeating pattern is referred to as periodic.
At the same time, Lothar Meyer published his own table of the elements organized by increasing atomic mass. 1830 - 1895
Both Mendeleev and Meyer arranged the elements in order of increasing atomic mass. • Both left vacant spaces where unknown elements should fit. So why is Mendeleev called the “Father of the Periodic Table” and not Meyer, or both? Could it be his dashing good looks?! Mendeleev published first!
Mendeleev left blank spaces in his table when the properties of the elements above and below did not seem to match. The existence of unknown elements was predicted by Mendeleev on the basis of the blank spaces. When the unknown elements were discovered, it was found that Mendeleev had closely predicted the properties of the elements as well as their discovery.
Predicted Properties Observed Properties Atomic weight 72 72.61 Density 5.5 g/cm3 5.32 g/cm3 Melting point 825 C 938 C Oxide formula RO2 GeO2 Density of oxide 4.7 g/cm3 4.70 g/cm3 Dates (predicted and found) 1871 1886 Color Dark gray Gray-white and the elusive element 32…
The Father of the Periodic Table After the discovery of these unknown elements between 1874 and 1885, and the fact that Mendeleev’s predictions 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 were 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
Remember This…?! In 1913, through his work with X-rays, Henry Moseley 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.” 1887 - 1915
Henry Moseley His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting in Gallipoli by a sniper’s bullet, at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.
When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. Periodic Law
The Current Periodic Table • Mendeleev wasn’t too far off. • Now the elements are put in rows by increasing ATOMIC NUMBER!! • The vertical columns are called groups or families and are labeled from 1 to 18 (modern) • or in A & B Groups (with Roman numerals)
Groups…Here’s Where the Periodic Table Gets Useful!! • Elements in the same group have similar chemical and physical properties!! • (Mendeleev did that on purpose.) • Why?? • They have the same number of valence electrons. • They will form the same kinds of ions.
Groups in the Periodic Table Elements in groups react in similar ways!
The horizontal rows are called periods and are labeled from 1 to 7. All elements in a period have the same number of energy levels (= to period #) Periods in the Periodic Table 11 1 2 3 4 5 6 7
n = 1 n = 2 n = 3 n = 4 Energy Levels
In addition to Group Labels, many of the groups have Family Names
Group 1A: Alkali Metals lithium Cutting sodium metal potassium
Alkali Metals • They are the most reactive metals. • They react violently with water. • Alkali metals are never found as free elements in nature - they are always in compounds with other elements. • Only 1 valence electron • Soft metals • Must be stored under mineral oil, etc.
Group 2A: Alkaline Earth Metals Magnesium
Group 2A: Alkaline Earth Metals Only 2 valence electrons Too reactive to be uncombined in nature. calcium strontium barium
Group 7A: The Halogens 7 valence electrons All non-metals Very reactive All physical states represented Colored gases (always poisonous!) Occur as diatomic molecules when pure fluorine Iodine I2 F2 Br2 Cl2 chlorine bromine
Noble Gases • Noble Gasesare colorless gases that are extremely un-reactive.(inert) • They are inactive because their outermost energy level is full. (8 valence electrons – except He which has 2) • Having 8 valence electrons is low in energy and, therefore, very stable.
Hydrogen • The hydrogen square sits atop Family IA, but it is not a member of that family. Hydrogen is in a class of its own. (An orphan?) • Like the Alkali metals, it only needs to lose one electron to be stable. (but it is not a metal!) • Sometimes it’s shown above 7A. • Like the Halogens, it only needs to gain one electron to have the stable Noble Gas electron configuration. (but it is not a Halogen!)
Hey Cameron, why are those elements by themselves on the bottom of the Periodic Table?!
I’ll handle this one, Cam! If they weren’t put on the bottom, the Periodic Table wouldn’t fit very nicely on a page! In fact, the table would look like this.
In fact, we have Glen Seaborg to thank for the fact that my Periodic Table doesn’t stick out of my notebook in a truly tasteless manner!
After co-discovering 10 new elements, in 1944 he moved 14 elements out of the main body of the periodic table to their current location below the Lanthanide series. These became knownas the Actinide series. Glenn T. Seaborg 1912 - 1999
He is the only person to have an element named after him while still alive. Glenn T. Seaborg "This is the greatest honor ever bestowed upon me - even better, I think, thanwinning the Nobel Prize." 1912 - 1999
There are many ways that we can break the Periodic Table up into sections!
Metals are good conductors of heat. That's why a branding iron is made from metal. The heat transfers quickly to the animal's hide.
Metals also conduct electricity. Notice that the Tesla coil sparks seek out metallic objects because they conduct electricity better than the nonmetallic materials such as wood or soil. Metals are also malleable and can be bent or hammered into various shapes.