Periodic Table Trends Atomic Radius Ionic Radius Ionization Energy Electronegativity
1. Atomic Radius Atomic Radius - distance from nucleus to outermost atom Measured by dividing the distance between 2 bonded identical gaseous atoms in half distance between nuclei 2
AR increases Atomic Radius increases to Francium! **A.R. is often measured in picometers (10-12 m)**
Explanation for A.R. Trend Are you adding energy levels (n) to give e - room to spread out as you add more electrons and protons? NO YES A.R. decreases (moving across period) A.R. increases (moving down a family)
Li n=2 Na n=3 K n=4 AR increases down a family A.R. Increases moving down a family because each period introduces a new energy level (new layer for e - to spread out)
A.R. decreases moving across a period because you aren t adding energy levels but increasing nuclear charge P Na 11 p + 15 p + Ar 18 p + AR decreases along period stronger nucleus can pull electrons in tighter and no new layers are added to spread out in
Atomic Radius Practice Who is bigger? F or O Na or Mg S or Cs He or Cl Who is smaller? Al or Fr I or Xe Be or Mg O or N
Atomic Radius Practice Who is bigger? F or O Na or Mg S or Cs He or Cl Who is smaller? Al or Fr I or Xe Be or Mg O or N
Ions Vocab Review What is an atom called if it gains an electron? What is an atom called if it loses an electron?
Ion Vocab Review What is an atom called if it gains electrons? What is an atom called if it loses electrons? anion - negative charge O O 2-8e- 10e - cation - positive charge Mg Mg 2+ 12e - 10e-
2. Ionic Radius Trend What happens to the radius when you add an electron to an atom? F Fluorine 9 p + 9 e -
Anion Radius When an electron is added (without increasing the nuclear charge) the repulsion of the electrons increase the radius Electrons are experiencing a smaller ratio of p + /e - so they are not being pulled in as tightly by the nucleus F Fluorine 9 p + 9 e - F - Fluorine ion 9 p + 10 e - adding e- increases radius
Cation Radius When electrons are removed the remaining electrons are pulled in tighter due to them experiencing a greater ratio of p + /e - Less electrons are repelling each other and sharing the positive nucleus The ionic radius decreases Na Na + Sodium 11 p + 11 e - Sodium ion 11 p + 10 e - removing e - decreases radius
Ion Trend Summary electrons radius anion neutral atom cation electrons radius
Ion Radius Practice Who is bigger? Who is smaller? Cl or Cl - Al or Al 3+ Na or Na + P or P 3-
Ion Radius Practice Who is bigger? Who is smaller? Cl or Cl - Al or Al 3+ Na or Na + P or P 3-
Ion Radius Practice Who is bigger? Cl Cl - Ar Na Na + Ne O O 2- Na +
Ion Radius Practice Who is bigger? Cl Cl - Ar Na Na + Ne O O 2- Na + Cl Cl - Ar 17p 18p 18e 18e same e - but Cl - has the weaker nuclear charge so it is bigger
Ion Radius Practice Who is bigger? Cl Cl - Ar Na Na + Ne O O 2- Na + Na Na + Ne 11p 10p 10e 10e n=3 n=2 Na has more energy levels for the electrons to spread out (closer to Fr)
Ion Radius Practice Who is bigger? Cl Cl - Ar Na Na + Ne O O 2- Na +
Ion Radius Practice Who is smaller? Al Al 3+ Ne Ne Na + O 2- S 2- Cl - Ar
Ion Radius Practice Who is smaller? Al Al 3+ Ne Ne Na + O 2- S 2- Cl - Ar Al Al 3+ Ne 13p 13e 13p 10e 10p 10e same e - but Al 3+ has a stronger nuclear charge so it is pulled in more tightly
Ion Radius Practice Who is smaller? Al Al 3+ Ne Ne Na + O 2- Stronger nuclear charge for same number of e - S 2- Cl - Ar
Ion Radius Practice Who is smaller? Al Al 3+ Ne Ne Na + O 2- S 2- Cl - Ar
3. Ionization Energy ionization energy - energy required to remove the outermost electron from an isolated atom in the gaseous state
IE increases across a period
IE increases up a family
I.E. Explanation smaller radius = higher I.E. smaller radius = electrons being pulled tighter to the nucleus so the outer electron is more difficult to remove (takes more energy to turn the atom into a cation) larger radius = electrons not being held as tightly so the outer electron is further from the nucleus and is easier to remove (takes less energy to turn the atom into a cation)
IE increases
Compare I.E. Who has a greater I.E., Na or Na +? Na Na + Sodium 11 p + 11 e - Sodium ion 11 p + 10 e - Removing e - decreases radius so the 10 e- left are pulled more tightly. Taking an e- off Na + would require a lot more energy!
Why is taking an e - off Ca 2+ so much harder than taking off an e - from Ca +? Anytime you take an e- off the radius decreases, electrons are pulled more tightly, and it is more difficult to remove another electron. Every successive electron removal requires more energy! Once an ion reaches noble gas status, removing another e- is crazy difficult!!!
Successive Ionization Energies I.E. jumps when you take off 1 e - past noble gas status noble gas status: looks like He
Key Idea for IE Removing valence e- is relatively easy. There is a huge jump in I.E. when removing core e-!
4. Electronegativity electronegativity - the ability to attract electrons in a chemical bond must be able to bond (so noble gases have NO electronegativity) smaller radius = higher electronegativity
Shared (bonded) electrons have a greater probability of being near F F is more electronegative H - 2.1 F - 4.0 Shared electrons have equal probability of being near either chlorine Cl - 3.0 Cl - 3.0
electronegativity increases to F
Electronegativity Explanation same as I.E. smaller radius = electrons attracted more tightly so nucleus can also attract other electrons that are shared with another atom (winning tug-of-war) larger radius = electrons are more weakly attracted and further from the nucleus, so electrons shared with another atom aren t pulled as tightly either (losing tug-of-war)
Trend Summary AR decreases IE increases Electronegativity increases
Trend Practice Who is bigger? Who is bigger? Co Mn Co Mn N Ga N Ga Sr Sr 2+ P 3- S 2- Ar K + Sr Sr 2+ P 3- S 2- Ar K +
Trend Practice Who has the higher IE? Co Mn Who has the higher IE? Co Mn N Ga N Ga Sr Sr 2+ P 3- S 2- Ar K + Sr Sr 2+ P 3- S 2- Ar K +
Trend Practice Who has more electronegativity? Who has more electronegativity? Co Mn Co Mn N Ga N Ga Rb Xe Rb Xe period 3? Cl
Shielding Effect Shielding Effect - the repulsive force exerted on valence electrons from core electrons more core electrons = more shielding increases AR lowers IE lowers electronegativity