Electrons are transferred between atoms to form positively or negatively charged atoms called ions. Due to the attraction of opposite charges, the ions are strongly attracted to one another.
All the atoms toward the left side of the periodic table have just one or two electrons in their outer shells, making them quite reactive- they want to get rid of them for a full outer shell.
Elements in Group 6 and 7 have nearly full outer shells, so they react to gain electrons for a full outer shell. They will then become a negative ion that is attracted to the now positive ion that it got the electrons from.
- The elements that most readily form ions are thoses in Groups 1, 2…