Periodicity Flashcards
definition of periodic
repeating pattern; in properties of the elements
similarties of elements in the same group
have a similar outer electron configuration
similarities of elemens in a period
have outer electrons in the same principal energy level ( a new row atrts when an electron enters a new shell)
similartities of elements in the same block
within a given block , the final electron is added to an orbital of that type
atomic radius variation across period
-decreases across a period–> across a period electrons enter the same shell, but there is an increase in nuclear charge (shielding remains approx constant). thus the elctrostatic force of attraction of the nucleus on outer electrons increases, resulting in a decrease in radius
atomic radius down a group
down a group, e- enter a new shell. shielding increases, there is a smaller attraction of the nucleus on the outer e-. the increase in proton number down a group does not compensae for hte increase in shielding effect.
IE across a period
increases along a period (few exceptions)
-e- enter the same shell across a period therefore shielding remains apprx constant. the proton number increases, the radius deceases–> increase of attraction between nucleus and outer e-. more energy is required
IE down a group
decreases down a group
e- enter a new shell, shielding and atomic radii increase. decrease in electrostatic froce of the nucleus on the outer e-. less energy needed.
melting point of period2
Li and Be have metallic bonding
B and C are macromolecular (C has a smaller radius than B and C-C bonds are shorter and therefore stronger than B-B bonds)
N O F Ne are almost all the same
remember to put gases below 0 on graph
melting point of period 3
Na and Mg and Al just have metalli cbonding
Si is macromolecular
P4, S8 and Cl2 are all simple molecular. S8 hsa the highest and Cl2 has the lowest.
Ar is atomic and so the lowest
polarising power
the ability of a positive ion to distort the electron cloud of a neighbouring ion. a high positive charge density leads to high polarising power
bonding in AlCl3 and BeCl2
both metallic covalent chlorides
both have high polarising power leading to an electron pair sharing, giving rise to covalent character.
AlCl3 forms dimers and BeCl3 is polymeric
PCl3
liquid at room temp
trigonal pyramidal
covalent cimple molecular
PCl5
solid at room temp —>ionic lattice
when in the gas state–> trigonal bipyramidal
ionic made of [PCl4]+ [PCl6]-
PCl5 is an empirical formula
why is PCl3 a liquid but PCl5 a solid?
ionic interactions are stronger than the pd-pd in PCl3, more energy needed
ionic chlorides with water
they do not undergo hydrolysis, just dissolve and form ions
MgCl2
Mg2+ has a high enough charge density that gives MgCl2 some covalent character. this allows for partial hydrolyss of MgCl2 ONLY WITH HEATING.
MgCl2 + H2O —> Mg(OH)Cl(s) + HCl
why cant solid MgCl2 be prepared by heating a solution of MgCl2?
it will undergo partial hydrolysis, therefore cannot be heated until crystallisation
reactions of chlorides of Li, Be,B ,C and N with water
LiCl Li+ and Cl-
BeCl2 + H2O —. Be(OH)2 + HCl
BCl3 + H2O —> H3BO3(s) + HCl boric acid
CCl4 no hydrolysis
NCl3 + H2O —-> NH3 + HClO chloric I acid
reactions of chlorides of Na,Mg,Al,Si,PCl3 and PCl5 with wtaer
NaCl–> Na+ and Cl-
MgCl2+ H2O —> Mg(OH)2 + HCl or just ions
AlCl3 + H2O —-> Al(OH)3 + HCl
SiCl4 + H2O —-> SiO2 + HCl
PCl3 + H2O —> HCl + H3PO3
PCl5 + H2O –> HCl + POCl3 phosphorus trichloride oxide
which is the chloride that does not produce HCl upon the reaction with water?
NCl3
examples of basic oxides
Na2O, MgO
acidic oxides examples
SiO2, CO2, P4O10, SO3, Cl2O
SiO2 in water
insoluble white solid (in water)
macromeluclar structure would require oo much energy to break covalent bonds.
