roshanirfan: Structure of Molecules 4.2.1 Notes on Drawing Dot and Cross Diagrams

CHEMISTRY NOTES FOR CLASS IX:

Dot-and-cross diagrams of ionic compounds

You need to be able to draw dot-and-cross diagrams to show the ions in some common ionic compounds. For example:

Examples of dot-and-cross diagrams

Compound	Diagram and properties
Sodium chloride, NaCl	Diagram of bonding in sodium chloride. A sodium atom gives an electron to a chlorine atom. The result is a sodium ion (2,8)+ and a chloride ion (2,8,8)-. Both ions have full outer shells. Sodium ions have the formula Na⁺, and chloride ions have the formula Cl⁻. You need to show one sodium ion and one chloride ion.
Magnesium oxide, MgO	Diagram of bonding in magnesium oxide. A magnesium atom gives two electrons to an oxygen atom. The result is a magnesium ion (2, 8) 2+ and an oxide ion (2,8) 2-. Both ions have full outer shells. Magnesium ions have the formula Mg²⁺, and oxide ions have the formula O²⁻. You need to show one magnesium ion and one oxide ion.
Calcium chloride, CaCl₂	Diagram of bonding in calcium chloride. A calcium atom gives one electron to one chlorine atom and another electron to a second chlorine atom. The result is a calcium ion (2,8,8) 2+ and two chloride ions (2,8,8)- , (2,8,8) -. All three ions have full outer shells. Calcium ions have the formula Ca²⁺, and chloride ions have the formula Cl⁻. You need to show two chloride ions because two chloride ions are needed to balance the charge on a calcium ion.

In the exam, make sure the dots and crosses are clear but don't worry about colouring them.

roshanirfan