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.

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)

PERIOD TREND (across - left to right): Radius Practice: K or Kr has the larger atomic radius Practice: K has the larger atomic radius

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

GROUP TREND (down - top to bottom) Practice: Ba or Mg has the larger atomic radius (AR) Practice: Ba has the larger atomic radius

Ionization Energy Ionization Energy is the energy required to remove the outermost_electron from an atom (in kilojoules)

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

Ionization Energy Practice: Br has a higher IE Practice: Ca or Br has a higher IE Practice: Br has a higher IE

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

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

Challenge: Challenge: Which element (from the entire periodic table) has the highest IE?___ _He_____

Electronegativity

Electronegativity Electronegativity is a measure of an atom’s ability to _take____ another atom’s electrons (no units). Electronegativity is abbreviated “EN”.

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

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 

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

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_____)

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

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.

NONMETALS – higher EN

Atomic Radius

Electronegativity

Ionization Energy

Reactivity

A Trick to Remembering the Trends: Snowman that falls over: Atomic Radius Metal Reactivity A&M likes to stand at football games!

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

The End Test on 12/17/2015