a measure of the net positive charge experienced by the outermost electrons

elements in the same period: Z_eff increases left to right

note: because protons are added 1 at a time increasing the positivitey of the nucleus thus increasing the attraction of the electrons

Z_eff is constant among elements within a given group because the increase of inner shell electrons negates the increase in the positivity of the nucleus

decreases from left to right across a period: because the increasing positive chage of the nucleus holds the outer electrons more closely and tightly

increases down a group: because the number of inner shells is increasing, separating the valence shell from the nucleus

the energy required to remove an electron completely from a gaseous atom of ion

process is always endothermic

increases from left to right across a period

decreases down a group

elements in Group I and II: low ionization energies

halogens: the smaller the atom, the higher the ionization energy

gain of electrons that results in a release of energy

always exothermic

increases across a period: strong electrostatic pull between nucleus and valence shell electrons = greater the energy release will be when the atom gains an electron

decreases in a group: because valence shell is farther away from the nucleus as principal quantum number increases

measure of the attractive force that an atom will exert on an electron in a chemical bond

greater electronegativity = greater attraction for bonding electrons

lower ionization energy = lower electronegativity

increases across a period

decreases down a group

high melting points and densities (exception: Li)

malleable

ductile

low Z_eff, low electronegativity, large atomic radius, low ionization energy

valence electrons are free to move = metals are good conductors of heat and electricity

brittle in the solid state and show little or no metallic luster

have high ionization energies, electron affinities, and electronegativities

have small atomic radii

poor conductors of heat and electricity

Group 1

posses most of the classic physical properties of metals except they have low densities

Group 2

possess many properties characteristic of metals

highly reactive nonmetals

group 7

found naturally as ions (halides)

Group 8

low boiling points

exist as gases at room temperature

Groups 3 to 12

very hard and have high melting and boiling points

malleable

good conductors

many different oxidation states