Chem 14A Scerri Midterm - Set 2
Terms in this set (8)
Explain what a triad is, its characteristics, and give an example.
* Triad groups were observed before the periodic table
* Way or organizing elements into sets of threes
* In the same vertical column in periodic table
* Middle element has characteristics approximately average of the top and bottom
* Atomic weight, reactivity, density, atomic number
* Reactivity increases down the triad
* EX: Lithium, Sodium, Potassium (Li, Na, K)
* EX2: Potassium, Rubidium, Cesium (K, Rb, Cs)
* These triads never start at the top of the block
* What ideas lead to the periodic table?
* Prout discovered that many elements had whole number multiples of the weight of Hydrogen
* Prout's Hypothesis: other elements made up of H-atoms
* True in the sense of protons
* Astrophysically, all elements literally formed from H and He
* What was Mendeleev's Periodic Table like?
* Originally ordered by atomic weight, because atomic numbers were not discovered yet
* Mendeleev actually made several predictions on the properties of undiscovered elements (Gallium, Germanium, Cesium)
* Had gaps in the table
* No noble gases
* Now known as the "short-form" table, with eight columns
* What is a pair reversal? Give an example.
* Certain elements get sorted into the wrong periodic group (column)
* Happens because atomic weights are averages of the isotopes
* This is solved when rearranging elements by Z, or atomic number
* Example is Argon and Potassium, or Tellurium and Iodine
* What numbers are associated with periodicity?
* Define periodic law.
* Chemical properties of elements are a periodic function of their atomic numbers
* What are the main types of periodic tables?
* Left-step uses orbital filling, not valence filling
* f-block, d, p, s
* Long form has the Lanthanides and Actinides included in the main body of the table, organized by valence shell filling
* Medium-long form is long form with the Lanthanides and Actinides separated and placed below
* Short form has 8 columns
* What are transuranium elements?
* Uranium is the last naturally occurring element, so anything after that
* Currently from 93 to 118, inclusive
* Few have practical applications
* Plutonium: nukes, Americium: smoke detectors
* Higher atomic numbers are more unstable
* Help test theories of nuclear stability
* Relativistic velocities of inner electrons make it difficult to study super-heavy elements
* Do not behave as expected based on periodicity
* First was neptunium in 1940
* Possible up to 137, or 172, or 173
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