Periodic Trends

1. Periodic Trends

2. Valence Electrons Electrons in the outermost principal quantum level of an atom Electrons in the same group (vertical column) have the same valence electron configuration

3. Trends • Transition Metals • d block • Lanthanide and Actinide Series • The sets of 14 elements following lanthanum and actinium • f block

4. Trends • Main Group • Groups of 1A-8A • Configurations are consistent • Metalloids (semi-metals) • Found along the border between metals and nonmetals • Exhibit properties of metals and nonmetals

5. Periodic Trends Atomic Properties

6. Ionization Energy • Energy required to remove an electron from an atom • Increases for successive electrons • Tends to increase across a period • Electrons in the same quantum level do not shield as effectively as electrons in inner levels • Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove

7. Ionization Energy • Decreases with increasing atomic number within a group • Compare nuclear charge • Higher the charge on the nucleus, the greater the attraction for electrons • Electrons farther from the nucleus are easier to remove • Effective nuclear charge (Zeff) is less • Zeff = Z - S • Penetration of the s and porbitals is greater than that of p or dorbitals • More electron shielding experience by electrons in a higher energy level

8. Ionization Energy • IE2 – the energy required to remove the second electron • In IIA vs IA – the second electron is easier to remove from IIA • The second electron (in IA) is in a lower “shell” and is harder to remove

9. Electronegativity • Measure of the tendency of an atom to attract a bonding pair of electrons • Measured on the Pauling scale • Most electronegative element (F) has a value of 4 • Decreases down a group • Atoms become “less good” at attracting bonding pairs • Nucleus is further away

10. Electron Affinity • The energy change associated with the addition of an electron • Tends to increase across a period • Tends to decrease as you go down in a group • Electrons farther from the nucleus experience less nuclear attraction • Some irregularities due to repulsive forces in the relatively small porbitals

11. Electron Affinity • First electron affinities have negative values • Shows a release of energy • As atoms get bigger, the incoming electron is further away from the nucleus and feels less attraction • Affinity falls as you go down the group

12. Atomic Radius • Determination of radius • Half of the distance between radii in a covalently bonded diatomic molecule • Covalent atomic radii • Periodic Trends • Radius decreases across a period • Increased effective nuclear charge due to decreased shielding • Radius increases down a group • Addition of principal quantum levels

13. Atomic Radius • Positive ion vs neutral atom • Positive ion is smaller • Number of electrons is lower (less repulsion) • Lanthanide Contraction • Electrons are filling the 4f orbitals

14. Properties of a Group Alkali Metals

15. The Alkali Metals • Easily lose valence electrons • React with halogens to form salts • React violently with water • Lithium is not the most reactive because the heat of reaction is insufficient to melt lithium and expose all of its surface area • Large hydration energy • Positive ionic charge makes ions attractive to polar water molecules • Radius and ionization energy follow expected trends