Explanation:
The atoms of elements such as hydrogen, sodium and potassium have only one electron in their outermost electron shell while atoms such as calcium, iron and chromium have several loosely held electrons. The bond would be almost entirely covalent. Ionic bonds form between atoms of very different electronegativities, e.g. sodium and chlorine, in which case the electron is largely removed from the sodium atom and transferred to the chlorine atom, resulting in sodium(+) chloride(-) ionic bonding
