A dot-and-cross diagram shows the outer electrons of atoms as dots and crosses, so you can see which electrons are transferred or shared and where each one came from.
A dot-and-cross diagram is a drawing that shows the outer electrons of atoms as dots and crosses, so you can see which electrons are transferred or shared and where each one came from. Malay: gambar rajah titik-dan-silang · Chinese: 点叉图.
The dots and crosses are just two symbols for electrons; using a different symbol for each atom lets you follow where every electron started. Only the valence (outer) electrons are drawn, because only these take part in bonding. For an ionic compound, the diagram shows electrons moving across from the metal to the non-metal and the resulting ions are drawn in square brackets with their charges. For a covalent molecule, the diagram shows the shared pairs sitting in the overlap between the atoms, along with any lone pairs.
Example. For sodium chloride you draw sodium losing its one outer electron (a cross) to chlorine, giving [Na]+ and a chloride ion [Cl]- with eight electrons, seven dots and the one cross. For water you draw the oxygen atom with two shared pairs, each made of one dot and one cross, plus two lone pairs, and each hydrogen with a duplet.
Confusion to avoid. Draw only the outer electrons, not the inner shells, and make sure hydrogen ends with a duplet, not an octet. In an ionic diagram remember the square brackets and charges; in a covalent diagram remember to include the lone pairs, because leaving them out is a frequent cause of lost marks.
The dot-and-cross diagram is the standard way this chapter asks you to show a bond, so drawing it neatly and correctly is a directly examined skill in SPM Chemistry.
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