Ionic bonding: electrons transfer from metals to non-metals

1. An ionic bond forms when a metal atom reacts with a non-metal atom.
2. An ion is a charged particle formed when an atom gains or loses electrons.
3. The metal atom loses the electrons in its outer shell and becomes a positively charged ion.
4. The non-metal atom gains those transferred electrons and becomes a negatively charged ion.
5. The number of protons never changes, so the charge comes only from the electrons gained or lost.
   1. For example, sodium loses one electron to form ${Na}^{+}$ while chlorine gains one to form ${Cl}^{-}$.

Group number: it predicts the charge on each ion

1. Group 1 metals
   1. A Group 1 atom has one electron in its outer shell.
   2. It loses one electron and forms an ion with a charge of $1+$, such as ${Na}^{+}$.
2. Group 2 metals
   1. A Group 2 atom has two electrons in its outer shell.
   2. It loses two electrons and forms an ion with a charge of $2+$, such as ${Mg}^{2+}$.
3. Group 6 non-metals
   1. A Group 6 atom has six electrons in its outer shell.
   2. It gains two electrons and forms an ion with a charge of $2-$, such as $O^{2-}$.
4. Group 7 non-metals
   1. A Group 7 atom has seven electrons in its outer shell.
   2. It gains one electron and forms an ion with a charge of $1-$, such as ${Cl}^{-}$.
5. For Group 1 and Group 2 metals, the positive charge equals the group number.
6. For Group 6 and Group 7 non-metals, subtract the group number from eight to find the size of the negative charge.

Noble-gas structures: electron transfer produces full outer shells

1. The noble gases in Group 0 have full outer electron shells, which makes them very stable.
2. Ions formed by Group 1, 2, 6 and 7 elements end up with the electronic structure of a noble gas.
3. A Group 1 or Group 2 atom reaches this structure by losing its incomplete outer shell.
4. A Group 6 or Group 7 atom reaches this structure by gaining enough electrons to fill its outer shell.
5. The element does not turn into a noble gas, because its number of protons stays the same.

Dot-and-cross diagrams: they show where each outer electron came from

1. Begin by drawing the correct number of outer-shell electrons for each metal atom and non-metal atom.
2. Use dots for one element and crosses for the other so you can track where each electron started.
3. Transfer the metal atom's outer-shell electrons to the non-metal atom.
4. Check that every metal atom loses the correct number of electrons and every non-metal atom gains the correct number.
5. Draw each resulting ion inside square brackets.
6. Write the ion's charge outside the brackets at the top right.
7. Finally, check that the non-metal ion has a full outer shell and that every transferred electron appears only once.

Four group pairings: the same charge rules build every required diagram

1. Group 1 metal with Group 7 non-metal, such as $NaCl$
   1. One metal atom transfers one electron to one non-metal atom, giving one $1+$ ion and one $1-$ ion.
2. Group 1 metal with Group 6 non-metal, such as ${Na}_{2}O$
   1. Two metal atoms each transfer one electron to one non-metal atom, giving two $1+$ ions and one $2-$ ion.
3. Group 2 metal with Group 7 non-metal, such as ${MgCl}_2$
   1. One metal atom transfers one electron to each of two non-metal atoms, giving one $2+$ ion and two $1-$ ions.
4. Group 2 metal with Group 6 non-metal, such as $MgO$
   1. One metal atom transfers two electrons to one non-metal atom, giving one $2+$ ion and one $2-$ ion.
5. In every ionic compound the positive and negative charges balance to give no overall charge.
6. You only need dot-and-cross diagrams for Group 1 and 2 metals combined with Group 6 and 7 non-metals at this level.