Lets say foxes hunt rabbits. If their are too many foxes then they will compete for the rabbits. The rabbits get outnumbered by the amount of foxes so the foxes kill all the rabbits and the rabbits could eventually go extinct.
The arrangement of particles that make up an ionic compound would be an ionic lattice type of crystal arrangement. An ionic lattice type of structure will be formed due to many of the ionic bonds formed between the oppositely charged ions of the metal and nonmetal.
Group 7a would have an ion charge of -1 because it has 7 valence electrons and it wants to gain one more electron(which is negative) to have a full shell of 8