First International Congress of Chemists
September 1860; group of chemists assembled in Karlsruhe, Germany, to settle the issue of atomic mass as well as some other matters that were making communication difficult
Canizzaro
presented a convincing method for accurately measuring the relative masses of atoms; enabled chemists to agree on standard causes for atomic mass and initiated a search for relationships between atomic mass and other properties of the elements
Mendeleev
includes new atomic mass values in a chemistry book; hoped to organize the elements according to their properties; arranged elements according to various properties and looked for trends and patterns; notices in order of increasing mass, certain similarit
periodic
trends appearing in repeating patterns/regular intervals
questions for mendeleev
why could most of the elements be arranged in order of increasing atomic mass but some could not?
what was the reason for chemical periodicity?
Moseley
examined the spectra for 38 different metals; discovered previously unrecognized pattern -- arranged elements by order of increasing (modern) atomic number/number of protons in the nucleus; ordered elements by nuclear charge
periodic law
the physical and chemical properties of the elements are periodic functions of their atomic numbers; when the elements are arranged in order of increasing atomic number, elements with similar properties appear at regular intervals
periodic table
an arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column (or group)
noble gases
argon discovered 1894 by Strutt and Ramsay (originally unnoticed b/c of its total lack of chem. reactivity); Helium discovered 1868 (as a component of the sun, based on the emission spectrum of sunlight; ramsay shows in 1895 that He exists on earth too);
Lanthanides
14 elements w/ atomic #s from 58(cerium, CE) to 71(lutetium, Lu); elements are so similar in chem and phys props, the process of separating & identifying was tedious and required much effort
Actinides
14 elements from 90(thorium, Th) to 103(lawrencium, Lr)
periods
horizontal rows on the periodic table
alkali metals
the elements of group 1; in their pure state, they all have silvery appearances and are soft enough to cut with a knife; are not found in nature as free elements, because they are so damn reactive; usually stored in kerosene b/c of their extreme reactivit
Alkaline-earth metals
Group 2; contain a pair of electrons in their outermost s sublevel; group config. for group 2 is ns^2; they are harder, denser, and stronger than alkali metals &have higher melting points; less reactive than alkali metals, but are also too reactive to be
Hydrogen
unique element w/ properties that do not closely resemble those of any group, although it has a ns^1 e config.
Helium
unique element w/ properties that do not match group 2 and is part of group 18 although it has a ns^2 config.; possesses chem. stability, exhibiting the unreactive nature of a group 18 element, whereas group 2 elements have no special stability; their hig
transition elements
the d-block elements/metals w/ typical metallic properties; good conductors of heat & electricity and have high luster; typically less reactive than alkali metals and alkaline earth metals; some are so unreactive they do not easily form compounds and exis
main-group elements
p-block elements w/ s-block elements; atoms of all pblock elements contain 2 e's in the ns sublevel; electrons add to a p sublevel only after the s sublevel in the same energy level is filled; pblock: the total # of electrons in the highest occupied level
Halogens
the elements of group 17; most reactive nonmetals; react vigorously w/ most metals to form examples of the type of compound known as salts; reactivity of halogens is based on the presence of 7 electrons in their outer energy levels (one short of the stabl
metalloids/semiconducting elements
mostly brittle solids w/ some props of metals, which are conductors, and some of nonmetals, which are nonconductors