Section 6.3 Periodic Trends

Objectives Compare period and group trends of several properties Relate period and group trends in atomic radii to electron configuration

Atomic Radius Electron cloud no defined edges 90% probability of finding an electron Size varies from substance to substance

Radius: Metals ½ distance between adjacent nuclei in a crystal of the element

Radius: Nonmetals ½ distance between nuclei of identical atoms that are chemically bonded

Trends within Periods The decrease from left to right All in same principal energy level Increased nuclear charge as you move to the right, which draws electrons closer to the nucleus.

Trends within Groups Increase from top to bottom Nuclear charge increases Electrons are added to higher principal energy levels Increase number of shells

Periodic Trends: Atomic Radius DECREASES I N C R E A S

Ions Atoms that gain or lose electrons negative or positive charge

Ionic Radius + charge = smaller radius - charge= larger radius

Lose Electrons/ +

Gain Electrons/ -

Trends within Periods L to R: positive ions’ radii decreases 5A: Size of larger negative ions decreases

Trends within Groups Ionic radii of both positive and negative ions increase as you move down a group

Ionization Energy Energy required to remove an electron from a gaseous atom Energy required to remove first electron is the first ionization energy Nuclei’s strength of hold on valence electrons

Ions and Ionization Energy 1A has low IE form positive ions 8A has high IE do not form ions

Beyond the 1st IE 2nd ionization energy = amount of energy needed to remove an electron from a 1+ ion 3rd IE = to remove e- from a 2+ ion

Trends within Periods First ionization energies increase L to R Inc. nuclear charge= inc hold on e-

Trends within groups First ionization energies decrease from top to bottom Valence electrons are farther from nucleus

Periodic Trends: Ionization Energy INCREASES D E C R A S

Octet rule Atoms tend to gain lose or share electrons to acquire a full set of 8 valence electrons Used to determine type of ion an element is likely to form

Electronegativity Relative ability of an atom to attract electrons in a chemical bond. Arbitrary units called Paulings

Electronegativity Trends Increases from L to R Except Noble Gases REASON: nuclear charge increases, more attraction to electrons in its outermost energy level Increases from top to bottom REASON: electrons are further away from the nucleus and better shielded from the nuclear charge

Periodic Trends: Electronegativity INCREASES D E C R A S