This is covalent network type of solid.
For example, silicon dioxide (SiO₂) is covalent network solid with covalent bonding.
Covalent network solid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material.
Silicon(IV) oxide has continuous three-dimensional network of SiO₂ units and diamond has sp3 hybridization.
This solids do not have free electrons so they are good insulators.
They have strong covalent bonds, so they melt at extremely high temperature.
Other examples are quartz, diamond, and silicon carbide.
More about network solid: brainly.com/question/15548648
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The atomic mass on the periodic table represents the sum of number of protons and number of neutrons.
Atomic mass = Number of protons + number of neutrons
Hope this helps!
The total mass would be 142.05 g/mol. Since sodium is 22.99 g/mol and there are 2 sodium atoms, it would be 45.98 g/mol. Divide 45.98 by 142.05 and you get 32.37%