Trend 1.1 of the Lithium Group (Group IA) Trends is that all metals are malleable and become softer down the column.
|Most Malleable||Least Malleable|
Why are metals malleable?
- Delocalized electrons/bonding
Electron Sea Model
- Delocalized electrons combine to form an electron sea
- This sea makes it possible for atoms to slide past each other
- The ability to slide past one another allows the metal to bend without breaking - The electron sea accommodates deformations/atom sliding by flowing into the new shape
- When many atoms are present in an atomic solid their molecular orbitals fuse to form bands
- Two bands are formed: one by the bonding orbitals (with electrons) and one by the anti-bonding orbitals (empty)
- When a metal is bent the ions are being displaced, the bands allow the delocalized electrons to adjust
- Malleability is possible because the adjustment of the delocalized electrons allows the structure to move without become significantly weaker
What allows for this delocalized bonding?
Metallic bonding: electron wave shared throughout a crystal lattice
Low electronegativities- tendency to lose electrons
-When metals bind together to form a solid, they donate electrons to the “sea”
Small number of valence electrons -There are too few electrons for regular 2-electron bonding
-To compensate, electrons are shared throughout the lattice forming the electron sea that holds the crystal lattice structures together.
Crystal Lattice Structures:
Why does malleability increase down the column?
As apart of the periodic trends, atomic radii increases down columns. The bigger the radius, the farther away the valence electrons are from the nucleus. The farther away the valence electrons are from the nucleus, the more polarizable the electron sea is. The more polarizable the electron sea, the more able atoms are to slide past one another. Therefore, malleability increases down the column.
- Tro, Nivaldo J. "Bonding in Metals: The Electron Sea Model." Chemistry: A Molecular Approach. 2nd ed. Upper Saddle River, NJ: Pearson Prentice Hall, 2011. 390+. Print.
- Chapter 6: Intramolecular and Intermolecular Forces and Molecular Energy; Chemical and Physical Bonding." Chapter 6: Intramolecular and Intermolecular Forces and Molecular Energy; Chemical and Physical Bonding. Web. 24 Apr. 2012. <http://www.wpi.edu/Academics/Depts/Chemistry/Courses/General/concept6.html>.
- Mosher, Michael, and Andrew Scott. "Metals." Chemistry: The Practical Science. By Paul Kelter. Vol. 10. Boston, MA: Houghton Mifflin, 2009. 551-52. Chemistry: The Practical Science. Charles Hartford. Web. 24 Apr. 2012.<http://books.google.com/books?id=VfcKIManfkUC&pg=PA552&lpg=PA552&dq=band+theory+and+malleability&source=bl&ots=CXWUVlKue7&sig=89KHc96ZxR7dfQuE9jvnNsYfTAo&hl=en&sa=X&ei=N-GWT6KKLcOugweFi-WODg&ved=0CEsQ6AEwBg#v=onepage&q=band%20theory%20and%20malleability&f=false>.