ch. 5 - periodic law Flashcards
how did Mendeleev group the elements?
organized in order of increasing atomic mass
predicted existence and properties of three remaining elements
how did Moseley group the elements?
organized in order of atomic number
Periodic Law
the physical and chemical properties of the elements are periodic functions of their atomic numbers
modern periodic table
elements w/ similar properties fall in the same group
elements ordered by atomic number
how are elements arranged?
vertically in groups, sharing chemical properties
horizontally in periods
group 1
alkali metals – soft, reactive, silvery
group 2
alkaline-earth metals – less reactive than g1, but still too reactive to be found in pure form in nature
hydrogen
unique element; light, reactive, gas
helium
special chemical stability
group 17
halogens – most reactive nonmetals, react w/ most metals forming salt
group 18
noble gasses – stable, usually unreactive, colorless, covalent shells
transition elements
d block elements; metallic properties
main-group elements
p and s blocks; varying properties
p block elements
nonmetals on right
metalloids forming staircase in middle
metals on lower left side – harder and denser than g2 but softer and less dense than d block metals
metalloids
semiconductors p block (staircase) located between nonmetals and metals
f block
between g3 & g4 in 6th and 7th periods
uranium = last naturally occurring element
n-2
lanthanides (first row) = shiny metals similar in reactivity to g2
actinides (second row) = radioactive
atomic radii
atomic radius = half the distance between the nuclei of identical atoms bonded together
decreases left to right – increasing positive charge of nucleus, attracting electrons towards it
decreases down to up – decreasing size of electron cloud as sublevels decrease
ionization energy
ionization energy = energy required to remove one electron from a neutral atom of an element
ionization - formation of an ion
increases left to right – increasing nuclear charge
increases down to up – more easily removable electrons
loses electron and takes energy
electron affinity
electron affinity = energy it takes for an atom to add an electron
increases left to right – increasing nuclear charge
increases down to up – large electron cloud = far electrons from nucleus
gains electron & gives off energy
ionic radii
decrease from left to right – electron cloud shrinks
decrease from down to up
cation
cation = positive ion
loss of electrons leading to decrease in atomic radius
anion
negative ion
addition of electrons increases atomic radius
valence electrons
electrons available to be lost, gained, or shared in order to form chemical compounds
often located in incompletely filled main-energy levels
electronegativity
ability of an atom to attract electrons
increases from left to right
increases from down to up
higher up = more electromagnetic
