Trends & the Periodic Table

Trends More than 20 properties change in predictable way based on location of element in PTMore than 20 properties change in predictable way based on location of element in PT Ex: density, melting point, atomic radius, ionization energy, electronegativityEx: density, melting point, atomic radius, ionization energy, electronegativity

Atomic radiusAtomic radius Ionization energyIonization energy ElectronegativityElectronegativity

Atomic Radius Atomic radius: defined as half the distance between neighboring nuclei in a molecule or crystalAtomic radius: defined as half the distance between neighboring nuclei in a molecule or crystal “size” varies a bit from substance to substance“size” varies a bit from substance to substance

Cannot measure the electron cloud: X-ray diffraction pinpoints nuclei to measure distance

Trends: Atoms get larger as go down a column – more principal energy levels

Fr Cs Rb K Na3 2-1Li2 1H1 ConfigurationElementPeriod Going down column 1: More principal energy levels as you go down, so it makes sense that the atoms get larger

previousprevious | index | nextindexnext Li: Group 1 Period 2 Cs: Group 1 Period 6

2-8NeVIIIA or FVIIA or OVIA or NVA or CIVA or BIIIA or BeIIA or 2 2-1LiIA or 1 ConfigurationElementFamily Going across row 2: You are still adding electrons – shouldn’t they get larger?!Atoms actually get a bit smaller as you go across a row What’s going on? You are still adding electrons – shouldn’t they get larger?! Atoms actually get a bit smaller as you go across a row What’s going on?

What do you remember about charge? opposites attract/like charges repelopposites attract/like charges repel valence electrons are pulled into atom by positive charge of nucleusvalence electrons are pulled into atom by positive charge of nucleus the greater the positive charge, the more pulling powerthe greater the positive charge, the more pulling power

So as you go across a row the size tends to decrease a bit because of greater “proton pulling power (PPP)” previousprevious | index | nextindexnext

Size  as you go  and size  as you go  previousprevious | index | nextindexnext

Ionization Energy Amount energy required to remove electron from an atomAmount energy required to remove electron from an atom Ionization energy = energy required to remove most loosely held valence electronIonization energy = energy required to remove most loosely held valence electron

Trends in ionization energy What do you think happens to the ionization energy as you go down a column of the periodic table?What do you think happens to the ionization energy as you go down a column of the periodic table? As you go across a row?As you go across a row?

Cs’ valence electron farther away from nucleus so electrostatic attraction is much weaker (easier to steal electron away from Cs) Cs’ valence electron farther away from nucleus so electrostatic attraction is much weaker (easier to steal electron away from Cs) previousprevious | index | nextindexnext

easier to steal electron from Li than Ne easier to steal electron from Li than Ne Li: less “proton pulling power” than Ne Li: less “proton pulling power” than Ne previousprevious | index | nextindexnext

Trends in ionization energy Ionization energy decreases as go down columnIonization energy decreases as go down column – easier to remove valence electron as gets farther away – easier to remove valence electron as gets farther away Ionization energy increases as go across a rowIonization energy increases as go across a row – it’s more difficult to remove valence electron due to PPP – it’s more difficult to remove valence electron due to PPP

Electronegativity Ability of atom to attract electrons in a bondAbility of atom to attract electrons in a bond Noble gases do not to form bondsNoble gases do not to form bonds –are inactive –don’t have electronegativity values Unit = PaulingUnit = Pauling Fluorine: most electronegative elementFluorine: most electronegative element –value: 4.0 Paulings

Trends in electronegativity Related to “proton pulling power (PPP)”Related to “proton pulling power (PPP)” Increases left to right across a rowIncreases left to right across a row Decreases top to bottom of a columnDecreases top to bottom of a column

Remember: F is the most electronegative element!

Reactivity of Metals metals are losers!metals are losers! judge reactivity of metals by how easily theyelectronsjudge reactivity of metals by how easily they give up electrons most active metals: Fr (#1) and Cs (#2)most active metals: Fr (#1) and Cs (#2) reactivity of metals goes up as ionization energy goes downreactivity of metals goes up as ionization energy goes down

Trends for Reactivity of Metals (AKA: Metallic Character) Increases as go down columnIncreases as go down column –Easier to lose electrons! Decreases as go across rowDecreases as go across row –Harder to lose electrons! Can you identify the K, Na, and Li in this clip? Can you identify the K, Na, and Li in this clip?

Reactivity of Non-metals non-metals are winners!non-metals are winners! judge reactivity of non-metals by how easily theyelectronsjudge reactivity of non-metals by how easily they gain electrons most active non-metal: fluorinemost active non-metal: fluorine reactivity of non-metals increases as electronegativity increasesreactivity of non-metals increases as electronegativity increases

Trend for Reactivity of Non-metals: depends on “proton pulling power” Increases as you go across a row (left to right)Increases as you go across a row (left to right) Decreases as you go down column (top to bottom)Decreases as you go down column (top to bottom) –shielded by more inner-shell electrons

Ionic Size Relative to Parent Atom Depends on if is positive ion or negative ionDepends on if is positive ion or negative ion How do you make a positive ion?How do you make a positive ion? How do you make a negative ion?How do you make a negative ion? Remove electrons Add electrons

How do you know if an atom gains or loses electrons? Think back to the Lewis structures of ionsThink back to the Lewis structures of ions Octet rule: valence # of 8Octet rule: valence # of 8 Metals have 1, 2, or 3 valence electronsMetals have 1, 2, or 3 valence electrons –easier to lose them Nonmetals have 5, 6, or 7 valence electronsNonmetals have 5, 6, or 7 valence electrons –easier to gain more Noble gases: have 8 so don’t form ionsNoble gases: have 8 so don’t form ions

Positive ions or cations Formed by loss of electronsFormed by loss of electrons Cations always smaller than parent atomCations always smaller than parent atom –lost electrons therefore smaller in size

Negative ions or anions Formed by gain of electronsFormed by gain of electrons Anions always larger than parent atomAnions always larger than parent atom –gained electrons therefore larger in size