Video Transcript
In a sample of calcium metal, how many electrons does an atom of calcium contribute
to the sea of delocalized electrons?
In order to identify how many electrons an atom of calcium contributes to the sea of
delocalized electrons, we need to first understand metallic bonds. Metallic bonds form when the electrons of metal atoms merge and form one sea of
delocalized electrons, as shown in the diagram using the example of lithium
metal. The metal atoms effectively turn into cations as their electrons release from the
valence shell of the atom to flow freely about the lattice of metal cations.
Metallic bonding is the electrostatic attraction between the metal cations and a
negatively charged sea of delocalized electrons. The sea of delocalized electrons contains only valence electrons, not core
electrons. Valence electrons occupy the outermost energy level of an atom, while core electrons
occupy inner energy levels. Let’s consider two examples of metals to understand this point.
We can begin with sodium. Sodium is a group one metal that has a single valence electron. Each sodium atom contributes one electron to the sea of delocalized electrons in
sodium metal. The sea of delocalized electrons in sodium has only one delocalized electron per
sodium cation present. Sodium has relatively weak metallic bonds.
Magnesium is a group two metal that has two valence electrons. Each magnesium atom contributes two electrons to the sea of delocalized electrons in
magnesium metal. Magnesium has relatively strong metallic bonds because it contains a higher number of
electrons in its sea of delocalized electrons per cation.
Group number indicates the number of valence electrons. Metals with a higher group number have more delocalized electrons per cation in the
lattice. Group one elements, called the alkali metals, have atoms with a single valence
electron that they contribute to their sea of delocalized electrons.
Alkali metals generally have lower melting points because they have weaker metallic
bonding. Group two metals are different from alkali metals. Group two metals contribute two electrons per cation to their sea of delocalized
electrons. These metals, called the alkaline earth metals, tend to have higher melting points
because of their stronger metallic bonds.
This question is asking us about calcium. Calcium is a group two metal and has two valence electrons. Each calcium atom contributes two valence electrons to the sea of delocalized
electrons in calcium metal. Therefore, in a sample of calcium metal, the number of electrons an atom of calcium
contributes to the sea of delocalized electrons is two.
