1. Rearrange this file to work in line with modeling activity for radii and 1st IE

2. Trends in Melting Point

3. Trends in Atomic Radius

4. Trends in Density

5. 7.12 Periodic Trends We will focus on three important trends:
Ionization Energy
Electron Affinity
Atomic (and Ionic) radius
Also need to know group trends for:
Melting points (Ch. 10)
Electronegativity (addressed in Ch. 8)

6. Periodic Properties of the Elements
Properties of atoms correlate with two main properties related to electronic configuration:
Principal energy level (n, the “shelf”)
Nuclear Charge
Other considerations:
Pairing Energy
Shielding Effect: effective nuclear charge is essentially the nuclear charge less the number of inner (core) electrons

7. 7.12 Ionization Energy El(g)  El+(g) + e- 1st IE
El+(g)  El2+(g) + e- 2nd IE
Which would require the most energy? Why?
See values in Tables 7.5 & 7.6 pg. 310
Note that there is a sudden jump after some of the electrons are removed. At which electron will this occur for a specific element? Why?

8. Ionization Energy (kJ/mol)

9. Trends in Ionization Energy
Successive ionizations require more energy than the 1st ionization energy by nearly a constant proportion.
But always reach a “jump” which shows a much greater increase. When will this “jump” occur?
Which elements have an unusually high ratio of 3rd IE to 2nd IE? th IE to 3rd IE?

10. Which element could this be?
Ionization energy plotted against the number of electrons removed.

11. Successive Ionization Energies
Explain the trend in increasing successive ionization energies:
Primary factor: charge
Other factor: quantum energy levels.
Less energy required to remove electrons that are already higher in energy
More more energy must be provided to remove electrons from lower energy orbitals.

12. Periodicity of First Ionization Energy

13. Trends in First Ionization Energy

14. Trends in First Ionization Energy
Trends mirror trends in metallic character

15. Trends in First Ionization Energy
Explain trends in first ionization energy on back of handout:
Trend across the period.
Trend down a family (group).
Include atomic model diagrams or electron configurations to support your explanation.

16. Trend Explanation Summary
Trend down a family (group).
Increasing energy levels of valence electrons (greater principal quantum number, n)
Trend across the period.
Increasing atomic number (charge of nucleus)

17. Trends in First Ionization Energy
Which member of each pair has the greater first ionization energy? Why?
Na or Na+
F or Cl
N or O
O or F
Be or B
K or Na

18. Trends in First Ionization Energy
Which member of each pair has the greater first ionization energy? Why?
Na or Na+
F or Cl
N* or O
O or F
Be or B*
K or Na

19. 7.12 Atomic Sizes
The edges of atoms are fuzzy, so size is difficult to measure. Can measure interatomic distances in molecules or between molecules during collisions. These give somewhat different results.
bonding or covalent radius
metallic radius
nonbonding radius
3:33

20. Atomic and Ionic Size Figure 6.31
Measure metallic or covalent radii by diffraction of X-rays See Figure 7.33

21. 7.12 Electron Shells and the Sizes of Atoms (p. 313)
As the principal quantum number increases, the size of the orbital increases.
All s orbitals are spherical and increase in size as n increases.
The distribution of electrons in an atom can be represented with a radial electron density graph, which shows the probability of finding an electron at a particular distance from the nucleus.

22. Electron Shells in Atoms
The ns orbitals all have the same shape, but have different sizes and different numbers of nodes.
Consider: He: 1s2 Ne: 1s2 2s22p6 Ar: 1s2 2s22p6 3s23p6

23. Radial Electron-Density Graphs
The radial electron density is the probability of finding an electron at a given distance.
For He there is only one maximum (for the two 1s electrons).
For Ne there are two maxima: one largely for the 1s electrons (close to the nucleus) and one largely for the n = 2 electrons (further from the nucleus).
For Ar there are three maxima: one each largely for n = 1, 2, and 3.

24. Radial Electron-Density Graphs
2s,2p 1s
2s,2p
3s,3p
The electron density maxima correspond to the electron shells (n values), which are diffuse and overlap with each other. The nuclear charge increases from 2+ for He to 18+ for Ar, resulting in a greater nuclear attraction for the inner shell electrons, so the 1s orbital of Ar is closer to the nucleus than the 1s orbitals of He and Ne. The electrons in the second energy level of Ar are closer to the nucleus than those of Ne. 1s
Note how the 1s electrons are pulled closer to the nucleus as the nuclear charge increases.

25. Radial Electron-Density Graphs
The maxima give the distance where it is most likely to find electrons with the different principal quantum number (shells).
These electron shells are diffuse and overlap a great deal.
These graphs illustrate one of the factors that affect the properties of the elements - the nuclear charge.

26. Trends in Size What factors might affect atomic or ionic size?
hydrogen
nitrogen
carbon
oxygen

27. Periodicity of Atomic Size

28. Atomic Radius
See Figure 7.34

29. Atomic Radius Decreases across a period, increases down a group
Explain trends…

30. Trends in Atomic Radius
Which member of each pair has the greater atomic radius? Why?
F or Cl
N or O
O or F
Na or Mg
K or Na

31. Trends in Ionic Radius (pm) (See Section 8.4)

32. Ionic Radius
Compare isoelectronic series of ions to see the effect of the factors

33. Which is larger? Na+ or Mg2+ Al3+ or P3- Ca2+ or Mg2+ K or Ca
O2- or F-

34. 7.12 Electron Affinities (p. 312)
El(g) + e-  El-(g)
Also can have successive values for addition of more electrons
Negative values indicate that energy is released
The largest negative values occur for the halogens
EA of Cl
08m13an1.mov

35. Electron Affinities (kJ/mol)

36. Electron Affinity
The most non-metallic elements have the most negative values

37. 7.13 & More: Metals, Nonmetals, and Metalloids
Elements can be grouped into three broad categories: metals, nonmetals, and metalloids.
These categories are primarily established by the electrical conductivity of the elements:
metals: electrical conductors
nonmetals: electrical insulators
metalloids: semiconductors

38. Elements of a type are grouped together in the periodic table

39. Metals
Metallic character refers to the properties of metals (shiny or lustrous, malleable and ductile, oxides form basic ionic solids, and tend to form cations in aqueous solution).
Metallic character increases down a group and decreases across a period.
Metals have low ionization energies.
Most neutral metals are oxidized rather than reduced.

40. Metals
When metals are oxidized they tend to form characteristic cations.
All group 1A metals form M+ ions.
All group 2A metals form M2+ ions.
Most transition metals have variable charges.
Most metal oxides are basic:
Metal oxide + water  metal hydroxide
Na2O(s) + H2O(l)  2NaOH(aq)

41. Nonmetals Nonmetals are more diverse in their behavior than metals.
When nonmetals react with metals, nonmetals tend to gain electrons:
metal + nonmetal  salt
2Al(s) + 3Br2(l)  2AlBr3(s)
Most nonmetal oxides are acidic:
nonmetal oxide + water  acid
P4O10(s) + 6H2O(l)  4H3PO4(aq)

42. Metalloids
Example: Si (shown here) has a metallic luster but it is brittle.
Metalloids are useful in the semiconductor industry.

43. Group Trends for the Active Metals
Correlates with position in periodic table, electronic configuration, ionization energy, electron affinity
Alkali Metals: Group 1A in the periodic table (Table 7.8 in your text)

44. Alkali Metals (p. 316) Alkali metals are all soft.
Their chemistry is characterized by loss of one electron: M  M+ + e-
They combine directly with most nonmetals: 2Na + Cl2  2NaCl
They react with water to form MOH and H2: 2Na + 2H2O  2NaOH + H2
Reaction with oxygen gives oxides (Li), peroxides (Na, K, Rb, Cs) and superoxides (K, Rb, Cs)

45. Trends in Reactivity of Alkali Metals
What trends would be predicted for the reaction of the alkali metals with air or water?
Video: Chemistry at Work video on Group I/water trends; Na/K + H2O video

46. Alkaline Earth Metals
Be Mg Ca Sr Ba

47. Alkaline Earth Metals Harder and denser than the alkali metals
Their chemistry is characterized by loss of two electrons: M  M2+ + 2e-
Be does not react with water. Mg will only react with steam. Ca, Sr, Ba react with water:
Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g)