Objectives
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Understand the differences between ionic and covalent bonds.
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Connect ionic and covalent bonds with physical properties of matter.
Introduction
Sugar and salt look so similar that most people cannot tell them apart without tasting them. Chemically, white refined table sugar, sucrose, and salt are very different. An ionic bond between a positive sodium ion and a negative chloride ion creates a molecule of sodiumchloride (NaCl). Covalent bonds between hydrogen, oxygen, and carbon atoms form to form a sucrose molecule (C12H22O11).
Ionic bonds form when oppositely Figure 1: The pile of white grains on the left are ordinary crystals of table salt and the grains on the right are charged atoms, referred to as ions, grains of white, refined sugar. Notice that the salt grains combine. Under the right conditions, are more cubic in shape. when individual sodium and chlorine atoms associate, an electron transfer will occur. The sodium atom contains a single electron in the valence energy level (the outermost electron orbit) and the chlorine atom contains seven electrons in its valence energy level, leaving an empty space for an eighth electron. Electrostatic forces cause the sodium atom to lose the extra electron. The chlorine atom attracts the free electron, creating a positively charged sodium ion (Na+), normally referred to as a cation. Now the chlorine atom, with an extra electron, has an overall negative charge (Cl-), and is referred to as an anion. © KC Distance Learning
The cation and anion with opposite electric charges are electrostatically attracted and form a neutrally charged, ionically bonded ion pair – in this case sodium chloride
(NaCl).
Na - e- → Na+ and
Figure 2: This valence electron model illustrates a sodium (Na) atom losing an electron to form a sodium cation (Na+). The free electron is transferred to the chlorine (Cl) atom forming a chloride (Cl-) anion.
Sodium-chloride (NaCl)
Cl + e- → Cl-
2Na + Cl2