Chemical Bonding: Further Explanation and Representations
Part 3
Metallic Bonds
Valence electrons in metals are not tightly bonded to each atom (due to a low ionization
energy). These electrons do not seem to belong to individual atoms but move easily from
one atom to another – the electrons are shared by all atoms in a metal. Metals can be
thought of as positive ions immersed in an atmosphere or “sea” of electrons
The mobile electrons exert a total attractive force on positive ions, “gluing” them
together. The ease of which the mobile electrons move within structure distinguishes
metallic bonds from ionic or covalent bonds.
Metallic bonds give rise to the properties of metals:
1. Good conductors of heat and electricity (due to mobile valence
electrons)
2. Hardness (binding actions of electrons [glue])
3. Luster (the way valence electrons absorb and reemit light that
strikes them)
4. Malleability – ability to be hammered without breaking
5. Ductility – ability to be stretched into wire without breaking
6. Sectility – ability to be cut into sections without breaking
Malleability, Ductility and Sectility are due to ions being able to flow in a sea of
electrons – they can shift and be rearranged.
Part 4:
Hydrogen Bonds
Hydrogen bonding is a special type of intermolecular attraction that exists between the
hydrogen atom in a polar bond (particularly an H-F, H-O or H-N bond) and an unshared
electron pair on a nearby small electronegative ion or atom (usually an F, O or N atom on
another molecule).
For example, a hydrogen bond exists between the H atom in an HF molecule and the F
atom of an adjacent HF molecule, F-H …F-H (where the dots represent the hydrogen bond
between the molecules.
Hydrogen bonds are very unique. They occur because molecules like F,N, and O
are so electronegative and hydrogen is not. Therefore a bond between hydrogen and any
of these three elements is very polar, with hydrogen at the positive end.
N-H
O-H
F-H
The hydrogen atom has no inner core of electrons, so the positive side of the bond is
nearly a bare proton! This positive charge is attracted to the negative chare of an
electronegative atom in a nearby molecule.
Hydrogen bonds are much weaker than ordinary chemical bonds, but still play an
important role in many chemical systems.
Note: Hydrogen bonding is what helps give water its properties
– it also gives snowflakes their unique shapes!
Questions:
1. Where are the electrons in a metallic bond?
2. What are 4 main properties of a metallic bond? What does each mean?
3. What is hydrogen bonding?
4. Why are hydrogen bonds unique?