Gen. Chem. Chapter 2

Effective Nuclear Change (Zeff)

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


elements in the same period: Zeff 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


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



Atomic Radius

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

Ionization energy

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

Electron Affinity

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)



low Zeff, 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

include boron, silicon, germanium, arsenic, antimony, tellurium, and polonium
Alkali Metals

Group 1

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

Alkaline Earth Metals

Group 2

possess many properties characteristic of metals


highly reactive nonmetals

group 7

found naturally as ions (halides)

Noble Gases

Group 8

low boiling points

exist as gases at room temperature

Transition Metals

Groups 3 to 12

very hard and have high melting and boiling points


good conductors

many different oxidation states


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