By Susan Elliott | Updated Aug 30, 2022
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Compounds may look simple, but they are the result of complex interactions at the atomic level. A shell model visualizes these interactions, revealing how electrons are distributed around nuclei. In the case of calcium chloride (CaCl₂), the model demonstrates the ionic bond formed when calcium donates two electrons to two chloride ions.
Divide your paper into four equal quadrants. Place two atoms at the top of the page and three at the bottom.
In the upper‑left quadrant, draw a small circle (~0.25 in.) to represent the chlorine nucleus. Measure 0.5 in. from its edge and draw three larger concentric circles, each 0.5 in. apart.
Imagine the drawing as a clock face: 12 o’clock at the top, 6 o’clock at the bottom, 3 o’clock on the right, and 9 o’clock on the left.
Place a dot on the first through third rings at 12 o’clock and repeat at 6 o’clock.
Add a dot to the outer two rings at 9 o’clock.
Place a dot on the centre ring at 3 o’clock.
Mark a dot on the outer two rings at 1, 5, 7 and 11 o’clock. Colour all chlorine dots green.
In the upper‑right quadrant, draw a small circle for the calcium nucleus. From its edge, measure 0.5 in. and draw four concentric circles, each 0.5 in. apart.
Place a dot on the first through third rings at 6 o’clock and 12 o’clock.
Insert a dot on the second ring at 3 o’clock and on the fourth ring at 9 o’clock.
Mark a dot on the second and third rings at 1, 5, 7 and 11 o’clock. Colour all calcium dots red.
Copy the chlorine atom into the bottom‑left quadrant without colouring the dots yet.
Position a calcium atom below the first one, centred on the bottom of the page.
Place another chlorine atom in the bottom‑right quadrant.
Remove one dot from the outer ring of the bottom calcium atom at 9 o’clock. Add a new dot to the outer ring of the left chlorine atom at 3 o’clock.
Draw an arrow to indicate the electron transfer from calcium to chloride. Colour the transferred dot red and the remaining chlorine dots green.
Erase another dot from the calcium’s outer ring at 3 o’clock. Place a new dot on the outer ring of the right chlorine atom at 9 o’clock and colour it red. Keep the other chlorine dots green.
Colour the remaining calcium dots red.
