chapters 6 & 7 chemistry 1l cypress creek high school
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Part 4: Periodic Trends 2TRANSCRIPT
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