How is the sea of electrons model is used to explain the physical properties of metals? electrons give off a charge, the greater or lesser the metal will depend on how packed the universe is in the metal, atoms and such.
Mutations can also be caused by exposure to specific chemicals or radiation. These agents cause the DNA to break down. This is not necessarily unnatural  even in the most isolated and pristine environments, DNA breaks down. Nevertheless, when the cell repairs the DNA, it might not do a perfect job of the repair.
If you change a nucleotide in DNA, every strand of RNA transcribed from it would be flawed throughout the cell's life. And if that cell divides, then you have two cells with the mutation and so on. This could possibly produce thousands of cells that have an incorrect gene sequence, which may kill the organism. So mutation of RNA is possible, but its effects are not noticeable, where as DNA mutations can have a rather drastic effect.