Periodic TrendsPeriodic Trends

What is a trend?What is a trend?

A trend is a predictable change in a A trend is a predictable change in a particular direction.particular direction.

Trends include ionization energy, Trends include ionization energy, reactivity, etc.reactivity, etc.

Ionization EnergyIonization Energy

The ionization energy is the energy The ionization energy is the energy required to remove an electron from required to remove an electron from an atom or ionan atom or ion

A + ionization energy = AA + ionization energy = A++ + e + e--

neutral atom = ion + electronneutral atom = ion + electron

Ionization TrendIonization Trend

Ionization energies Ionization energies decrease down a decrease down a group. (increase up group. (increase up a group) a group)

Ionization energies Ionization energies increase across a increase across a periodperiod

Electron ShieldingElectron Shielding

As you move down in a group, the number As you move down in a group, the number of electrons increase and the energy level of electrons increase and the energy level increases.increases.

The inner electrons shield the outer shell The inner electrons shield the outer shell electrons from the attractive pull of the electrons from the attractive pull of the nucleusnucleus the reduction in the attractive force of the the reduction in the attractive force of the

positively charged nucleus and the outermost positively charged nucleus and the outermost electrons due to cancellation of some + charges electrons due to cancellation of some + charges by the eby the e--..

Electron Shielding Electron Shielding ConstantsConstants

Atomic RadiusAtomic Radius

Atomic radius is not determined by Atomic radius is not determined by measuring the radius of one atom, measuring the radius of one atom, but 1/2 the distance between 2 but 1/2 the distance between 2 adjacent nuclei (internuclear adjacent nuclei (internuclear distance)distance)

•Internuclear distance

•Atomic Radius

Atomic Radii TrendsAtomic Radii Trends

Atomic radii Atomic radii increase as increase as you move you move down a group down a group and and decreases as decreases as you move you move across a across a period.period.

ElectronegativityElectronegativity

Electronegativity is the measure of Electronegativity is the measure of an atom in a chemical compound to an atom in a chemical compound to attract electronsattract electrons

Linus Pauling created a chart of Linus Pauling created a chart of electronegativity valueselectronegativity values

Electronegativity TrendsElectronegativity Trends

Electronegativity decreases as you Electronegativity decreases as you move down a group and increases move down a group and increases across a periodacross a period

Summary of Periodic Summary of Periodic Table TrendsTable Trends

Moving Left --> Right Moving Left --> Right Atomic Radius Decreases Atomic Radius Decreases Ionization Energy Increases Ionization Energy Increases Electronegativity Increases Electronegativity Increases

Moving Top --> Bottom Moving Top --> Bottom Atomic Radius Increases Atomic Radius Increases Ionization Energy Decreases Ionization Energy Decreases Electronegativity Decreases Electronegativity Decreases

IonsIons

Atoms form ions by either gaining or Atoms form ions by either gaining or losing electrons.losing electrons.

Ionic radii decrease across the period Ionic radii decrease across the period and increases down the groupand increases down the group

Ionic Radius TrendsIonic Radius Trends

MetalsMetals Ionic radius decreases from left to right.Ionic radius decreases from left to right. Ionic radius increases down the chartIonic radius increases down the chart

Non-metalsNon-metals Ionic radius decreases from left to rightIonic radius decreases from left to right Ionic radius increases down the chartIonic radius increases down the chart

HOWEVER:HOWEVER: Non-metallic ions are larger than metallic Non-metallic ions are larger than metallic

ionsions Decrease across the row, until you reach Decrease across the row, until you reach

the non-metalsthe non-metals

Electron AffinityElectron Affinity

The energy change that occurs when The energy change that occurs when a neutral atom gains an electron is a neutral atom gains an electron is electron affinityelectron affinity

Electron affinity increases across a Electron affinity increases across a period and decreases down a groupperiod and decreases down a group