1. Periodic Properties of Elements

2. Periodic Trends In this chapter, we will explain observed trends in:
Sizes of atoms and ions
Ionization energy (losing electrons)
Electronegativity (affinity or attraction for electrons)

3. Atomic Radius or Atomic Size
The atomic radius is the distance between the nucleus and the outer edge of the electron cloud.
Defined as one-half of the distance between two atoms when they collide.

4. Trends in Atomic Size In general, atomic size:
increases from top to bottom within a group and
increases from right to left across a period.
This diagram lists the atomic radii of seven nonmetals. An atomic radius is half the distance between the nuclei of two atoms of the same element when the atoms are joined.

5. Trends in Atomic Size

6. Trends in Atomic Size
This diagram lists the atomic radii of seven nonmetals. An atomic radius is half the distance between the nuclei of two atoms of the same element when the atoms are joined.

7. Atomic radius vs. atomic number
04/10/99

8. Ion Size Metals lose electrons: cation (positive charge)
Cations are always smaller than the original atoms.
When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes?
Na+ has valence electrons in energy level 2 more pull on valence electrons – smaller ion.

9. Ions Non-metals gain electrons: anion (negative charge)
Anions are always larger than the original atoms.
When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes?
More electrons, more repulsion, so electrons “spread out”: larger atom.

10. Trends in Ionic Size The size of ions:
Cations (LOSE ELECTRONS) are always smaller than the original atoms.
Anions (GAIN ELECTRONS) are always larger than the original atoms.

11. Trends in Ionic Size
The trend generally follows the atomic size trend. Cannot compare a trend across an entire period – must use separate trends for metals and non-metals.

12. Ionization Energy
Amount of energy required to remove an electron from an atom.
First ionization energy: energy required to remove first electron.
Second ionization energy: energy required to remove second electron, etc.

13. Trends in Ionization Energy
First ionization energy:
increases from bottom to top within a group, and
increases from left to right across a period.

14. Trends in First Ionization Energies
As one goes down a column, less energy is required to remove the first electron.

15. Trends in First Ionization Energies

16. Trends in Electronegativity
Electronegativity is the ability of an atom to attract electrons when the atom is in a compound *
* Fluorine has the highest electronegativity

17. Trends in Electronegativity
Fluorine has the highest electronegativity.
Noble gases have zero electronegativity (they already have a full valence shell)

18. Effective Nuclear Charge, Zeff
the charge felt by the valence electrons after taking into account the affect of shielding electrons between them and the nucleus.

19. Effective Nuclear Charge, Zeff
Zeff = (# of protons) – (# of inner shell electrons)
= (atomic #) – (# non-valence electrons)
Zeff = Z - S

20. Coulomb’s Law Relates energy of attraction of the nucleus to a valence electron with the charge and distance.

21. Coulomb’s Law Relates energy of attraction of the nucleus to a valence electron with the charge and distance.
Li has larger relative E, so STRONGER pull on the electrons.

22. Periodic Trends COMPARE TRENDS IN PERIODS –Al & Na Atomic Radius:
Atomic Radius:
smaller larger
Ionization Energy:
higher lower
Electronegativity:

23. Periodic Trends

24. ISOELECTRIC SERIES
What is the trend of atomic size for these isoelectric atoms/ions?
N3- O2- F- Na+ Mg2+ Al3+
“Isoelectronic” means ions/atoms with the same number of electrons.
Each has 10 electrons.
Decreasing radius with increasing # of protons. (Due to stronger pull from MORE protons.)

25. ISOELECTRIC SERIES

26. Which is larger: Na+ or Na?

27. Correct Answer:
Na+ Na
Both have the same number of protons, but Na with one more electron will be larger.

28. Which is larger: Cl or Cl?

29. Correct Answer:
Cl Cl
Both have the same number of protons, but Cl− with one more electron will be larger.

30. Trends in First Ionization Energies
Discontinuities:
The first occurs between Groups 2 and 3.
Electron removed from p-orbital rather than s-orbital
e- is farther from nucleus
repulsion by s electrons.

31. Trends in First Ionization Energies
Discontinuities:
The second occurs between Groups 5 and 6.
e- removed from doubly occupied orbital.
Repulsion from other electron in orbital helps its removal.

32. Ionization Energy
It requires more energy to remove each successive electron.
When all valence electrons have been removed, the ionization energy shows a HUGE increase.

33. Ionization Energy
Using the data below, determine the number of valence electrons for each atom.
# Valence electrons: I1
740
790
580 I2
1,200
1,500
1,800 I3
8,000
3,200
2,700 I4
10,000
4,400
11,600 I5
14,000
16,090
16,000

34. Atom e- Photoelectron Spectroscopy Ephoton = hv
X-rays bombard the atom and electrons are released. The energy required to remove each electron is measured and reported on the Spectrum graph.
Photoelectron Spectroscopy
Atom
Ephoton = hv
Monochromatic
Beam of X-Rays e-

35. Photoelectron Spectrum (PES)
The x-axis of the PES graph shows the relative “binding energy” (very similar to ionization energy) of electrons in an atom. (Note: many (but not all) PES graphs DECREASE in value from left to right.)
The y-axis shows the relative number of electrons for each sub-level.

36. Photoelectron Spectrum
A method to identify the placement of electrons for a SINGLE atom. 3p 2p 3s 1s 2s 4s

37. Photoelectron Spectrum
Identify the sublevel and number of electrons for each peak
1s2
2s2
Boron
2p1

38. Photoelectron Spectrum
Identify the sublevel and number of electrons for each peak.
2p6
3p6
Calcium
1s2
3s2
2s2
4s2

39. Photoelectron Spectrum
Why are Ca peaks higher in energy than K?
Ca has more protons and higher Zeff, so stronger pull on e-

40. Photoelectron Spectrum
TRUE OR FALSE: The PES for Ca2+ and Ar are the same.
Hint: They are Isoelectric (both have 18 electrons)
NO! Ca2+ has more protons, so will have a stronger pull on the electrons. So Ca2+ peaks should have HIGHER binding energy.

41. Photoelectron Spectrum
TRUE OR FALSE: The PES for 16O and 18O are the same.
Hint: How many protons and electrons do each have?
YES! The only difference between the two isotopes is the number of neutrons, which have neutral charges. It won’t affect the energy of attraction, so no difference.

42. Photoelectron Spectrum
Why is the last peak (on the right) for Scandium assigned to 3d instead of 4p?