• Ionic bonds form between two atoms when one or more electrons are completely transferred from one atom to the other. The atom that gains electrons has an overall negative charge, and the atom that donates electrons has an overall positive charge. Because of their positive or negative charge, these atoms are ions. The attraction of the positive ion to the negative ion constitutes the ionic bond. Sodium (Na) and chlorine (Cl) form ions (Na + and Cl – ), which attract one another to form the ionic bond in a sodium chloride (NaCl) molecule. A plus or minus sign following a chemical symbol indicates an ion with a positive or negative charge, which results from the loss or gain of one or more electrons, respectively. Numbers preceding the charges indicate ions whose charges are greater than one (Ca 2+ , PO 4 3– ). • Covalent bonds form when electrons are shared between atoms. That is, neither atom
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