Unit 7: Periodic Unit 7: Periodic TableTable

Chapters 6 & 7Chemistry 1L

Cypress Creek High School

Part 4:Part 4:Periodic Periodic TrendsTrends

Periodic Table TrendsPeriodic Table TrendsPatterns on the periodic table

Atomic RadiusIonic RadiusElectronegativityIonization Energy

Periodic TrendsPeriodic TrendsDepend upon 4 important factors…

Energy levels – the horizontal rows; ranked from 1-7 based on energy and distance from the nucleus

Valence electrons – number of electrons in outermost energy level

Shielding effect – the decrease in the attraction between the outer electrons and the nucleus due to the presence of other electrons between them

Nuclear charge – depends on the number of protons – the more protons in the nucleus, the greater pull they have on their surrounding electrons

Atomic RadiusAtomic RadiusAtomic radius is half the

distance between the centers of two atoms that are just touching each other

Influenced by 2 factorsThe number of energy levelsThe nuclear charge (pull of the

positively charged nucleus on its electrons)

The more energy levels, the ________ the atomic radius.(larger/smaller)

The more protons in the nucleus, the ________ the atomic radius. (larger/smaller)

larger

smaller

Atomic Radius TrendAtomic Radius TrendAtomic radius increases as you move down a groupAtomic radius decreases as you move from left to right

in a period

Ionic RadiusIonic RadiusMetals lose electrons to form cations

Li Li+

F F-

Nonmetals gain electrons to form anions

Atomic radius decreases - energy level is lost or “shed” (think of peeling an onion)

Atomic radius increases - energy level expands because it is more “crowded” and electrons exert greater repulsive forces on each other (think of 7 people vs. 8 people holding hands in a circle)

Ionic Radius TrendIonic Radius Trend Ionic radius increases as you move down a group Ionic radius decreases as you from left to right in a

period BUT… Energy levels change between cations and anions Note: metals make smaller ions, nonmetals make larger ions

decreasing ionic radius

Atomic & Ionic Radius TrendsAtomic & Ionic Radius Trends

ElectronegativityElectronegativity Electronegativity is a measure of how easily an atom attracts the

valence electrons of another atom Numbers are assigned to each element to rate the electronegativity

(from 0.7 to 4.0) Low electronegativity = does not want to attract valence electrons (metals) High electronegativity = really wants to attract valence electrons (nonmetals)

Influenced by 2 factors: Valence electrons Shielding

Electronegativity TrendElectronegativity TrendElectronegativity decreases as you move down a groupElectronegativity increases as you from left to right in

a period

Ionization EnergyIonization Energy Ionization Energy – the energy needed to remove the outermost

electron in an atom Influenced by 2 factors:

Nuclear charge – more protons pulling on the electrons, making it harder to remove them

Shielding – Radius is larger; outer electrons are farther from the nucleus; more difficult to gain electrons

Ionization EnergyIonization Energy First ionization energy is that energy

required to remove the first electron Ex: Easiest to remove Na’s first

electron, hardest to remove Ar’s first electron

Second ionization energy is that energy required to remove the second electron Ex: Easiest to remove Mg’s

second electron, hardest to remove Na’s second electron

Third ionization energy is that energy required to remove the third electron Ex: Easiest to remove Al’s third

electron, hardest to remove Mg’s third electron

Fourth, fifth, sixth etc… the ionization energy patterns continues

This graph shows first ionization energy only!

Ionization Energy TrendsIonization Energy Trends Ionization energy decreases as you move down a group Ionization energy increases as you from left to right in a period

Summary of Periodic TrendsSummary of Periodic Trends