7 Periodic Properties of the Elements
periodic table
development
Dmitri Mendeleev & Lothar Meyer
elements in the same group generally have similar chemical properties
periodic trends
sizes of atoms and ions
ionization energy
electron affinity
effective nuclear charge
Z(eff) = Z - S
bonding atomic radius
one-half of the distance between covalently bonded nuclei
decrease from left to right across a row
increase from top to bottom of a column
sizes of ions
the nuclear charge
the number of electrons
the orbitals in which electrons reside
ionic size decreases with an increasing nuclear charge
anions are larger than their parent atoms
electrons are added and repulsions between electrons are increased
ions increase in size as you go down a column
this is due to increasing value of n
cations are smaller than their parent atoms
the outermost electron is removed and repulsions between electrons are reduced
the amount of energy required to remove an electron from the ground state of a gaseous atom or ion
the first ionization energy: energy required to remove first electron
when al valence electrons have been removed, the ionization energy takes a quantum leap
trends in frist ionization energies
the size of the nuclear charge
in general, ionization energy increases as the proton number increases
distance of outer electrons from the nucleus
the further the outer electrons shell is from the nucleus, the lower the ionization energy
shielding effect of inner electrons
the ionization energy is lower as the number of full electron shells between the outer electrons and the nucleus increases
as the atomic number increases, the positive nuclear charge increases
the force of attraction between positive and negative charges decrease rapidly as the distance between them increase
full inner shells prevent the full nuclear charge being felt by the outer electrons
spin-pair repulsion
extra repulsion between the pair of electron
ex.
Be ----> B
Mg ---> Mg+ + e-
further away from the nucleus, less energy is required for it to be expelled from the atom
[Ne]3s2 3p1 ---> [Ne]3s1
3p energy is higher than 3s
[Ne]3s2 3p3 ---> [Ne]3s23p2
spin repulsion: easier to loss
the energy change accompanying the addition of an electron to a gaseous atom
trends
in general, electron affinity becomes more exothermic as you go from left to right across a row
discontinuities
IA & IIA
the added electron must go in a p-orbital, not an s-orbital
the electron is farther from nucleus and feels repulsion from s-electrons
IVA & VA
group VA has no empty orbitals
the extra electron must go into an already occupied orbital, creating repulsion
metal, nonmetals, and metalloids
metals
tend to form cations
nonmetals
tend to form anions
tend to be lustrous, malleable, ductile, and good conductors of heat and electricity
compounds formed between metals and nonmetals tend to be ionic
metal oxides tend to be basic
dull, brittle substances that are poor conductors of heat and electricity
tend to gain electrons in reactions with metals to acquire a noble gas coonfiguration
substances containing only nonmetals are molecular compounds
most nonmetal oxides are acidic
metalloids
have some characteristics of metals and some of nonmetals
group trends
alkali metals
soft, metallic solids
are found in compounds in nature, not in their elemental forms
have low densities and melting points
have low ionization energies
their reactions with water are famously exothermic
alkali earth metals
have higher densities and melting points than alkali metals
their ionization energies are low, but bot as low as those of alkali metals
group 6A
oxygen, sulfur, and selenium are nonmetals
tellurium is a metalloid
the radioactive polonium is a metal
oxygen
sulfur
tends to take electrons from other elements
a weaker oxidizer than oxygen
group VIIA
Halogens
prototypical nonmetals
have large, negative electron affinities
react directly with metals to form metal halides
group VIIIA
noble gases
have astronomical ionization energies
electron affinities are positive
are found as monatomic gases
relatively unreactive
tend to oxidize other elements easily