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5.2 PERIODIC TRENDS A. Atomic Radius The atomic radius of a chemical element is a measure of the size of its atoms and is the _distance from the nucleus to the boundary of the surrounding cloud of electrons.
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PERIOD TREND (across - left to right): Radius
As atomic # INCREASES, AR _decreases_ For each element across a period, one proton and one electron are added to the outermost energy level. As NUCLEAR CHARGE increases (nucleus is more ++), electrons are pulled _inward____ (opposites attract)
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PERIOD TREND (across - left to right): Radius
Practice: K or Kr has the larger atomic radius Practice: K has the larger atomic radius
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GROUP TREND (down - top to bottom)
As atomic # INCREASES down a group, AR __increases__ For each element down a group, an ENERGY LEVEL is added to the atom. Nuclear charge increases, but __shielding__also increases. SHIELDING – as energy levels are added, electrons are less affected by positively charged nucleus because electrons repel each other. Practice: Ba / Mg has the larger atomic radius
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GROUP TREND (down - top to bottom)
Practice: Ba or Mg has the larger atomic radius (AR) Practice: Ba has the larger atomic radius
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Ionization Energy Ionization Energy is the energy required to remove the outermost_electron from an atom (in kilojoules)
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Ionization Energy PERIOD TREND (across - left to right):
As atomic # INCREASES, IE __increases Nuclear charge increases; ___electrons__ are held more __closely______ to the nucleus Also, outer energy level is closer to being an _octet__ Practice: Ca / Br has a higher IE
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Ionization Energy Practice: Br has a higher IE
Practice: Ca or Br has a higher IE Practice: Br has a higher IE
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Ionization Energy GROUP TREND (down - top to bottom)
As atomic # INCREASES , IE _decreases_______ Outer electrons are in __higher_ energy levels Farther from nucleus, more ___easily_______ removed Practice: Na / Cs has a higher IE
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Ionization Energy Practice: Na / has a higher IE GROUP TREND
(down - top to bottom) Practice: Na / Cs has a higher IE Practice: Na / has a higher IE
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Challenge: Challenge: Which element (from the entire periodic table) has the highest IE?___ _He_____
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Electronegativity
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Electronegativity Electronegativity is a measure of an atom’s ability to _take____ another atom’s electrons (no units). Electronegativity is abbreviated “EN”.
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Electronegativity PERIOD TREND (across - left to right):
As atomic # INCREASES EN ___increases_____. Metals tend to___lose________ electrons Nonmetals tend to ____gain________electrons (to fulfill the ____octet__________ Rule) Practice: Be / O has a higher EN
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Electronegativity GROUP TREND (down - top to bottom)
As atomic # INCREASES, EN ___decreases_______ Elements at __top___ of group have e– closely held by nucleus because they are closest to nucleus. Elements at bottom of group have more _distance____ between nucleus and outer e– Practice: N / Sb has a higher EN
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Electronegativity Practice: N has a higher EN Fi Electronegativity
Why are noble gases not EN? They have complete octet. There is no driving force for them to take or give up electrons
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Reactivity Reactivity refers to how __likely________ an atom is to react with other substances. Reactivity depends on ... 1. How easily electrons can be removed (__ionization energy___) 2. How easily atoms grab electrons (___electronegativity_____)
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Reactivity Reactivity of Metals – low ionization energy
PERIOD TREND (across - left to right):- As atomic # INCREASES, reactivity ____decreases_________ GROUP TREND (down - top to bottom) - As atomic # INCREASES, reactivity ____increases_____________ WHY? If IE is low, an atom is more likely to lose an electron, which results in a chemical reaction with another atom
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Reactivity Reactivity of Nonmetals – high electronegativity
PERIOD TREND (across - left to right): - As atomic # INCREASES, reactivity _____increases_________ GROUP TREND (down - top to bottom): - As atomic # INCREASES, reactivity _____decreases______ WHY? IF EN is high, the atom takes electrons from other atoms more easily, which results in a chemical reaction.
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NONMETALS – higher EN
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Atomic Radius
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Electronegativity
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Ionization Energy
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Reactivity
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A Trick to Remembering the Trends:
Snowman that falls over: Atomic Radius Metal Reactivity A&M likes to stand at football games!
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A Trick to Remembering the Trends:
Snowman standing on his head and then he falls over: Electronegativity **EINstein like to do Ionization Energy headstands!! Nonmetal Reactivity
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The End Test on 12/17/2015
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