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Ionic Compounds

Ionic Compounds. Unit 4 PreAP Chemistry McKinney HS. What is an ionic compound?. Composed of a metal and a nonmetal Solid formed from a lattice-style repetition of anions(-) and cations(+)

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Ionic Compounds

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  1. Ionic Compounds Unit 4 PreAP Chemistry McKinney HS

  2. What is an ionic compound? • Composed of a metal and a nonmetal • Solid formed from a lattice-style repetition of anions(-) and cations(+) • Formula represents the ratio of cations to anions in the crystal lattice, and is called a “formula unit” • Usually have high melting points • Electrically non-conductive as a solid • Conductive as molten liquids or in solution

  3. Formation of an ionic compound • Combines a metal and a nonmetal through the transfer of electrons • Example: A compound made from potassium and chlorine

  4. Potassium has one valence electron and tends to lose it to become a cation with a charge of +1 K Cl Chlorine has seven valence electrons and tends to gain one to become an anion with a charge of -1

  5. K Cl

  6. Potassium, being an alkali metal, has an oxidation number of +1 - + K Cl Chlorine, being a halogen, has an oxidation number of -1

  7. When these two ions combine to form an ionic compound, they will combine in such a way that the overall charge of the compound is zero. In this case, the smallest ratio that adds up to zero is one potassium ion and one chloride ion. - + K Cl

  8. When these two ions combine to form an ionic compound, they will combine in such a way that the overall charge of the compound is zero. In this case, the smallest ratio that adds up to zero is one potassium ion and one chloride ion. KCl Note that the metal ion is ALWAYS written first, and that when there is only one ion of an element, it is not necessary to place a subscript “1” next to that element.

  9. Calcium has two valence electron and tends to lose both of them to become a cation with a charge of +2 Ca Cl Chlorine has seven valence electrons and tends to gain one to become an anion with a charge of -1

  10. Since calcium has two electrons to give, but chlorine can only accept one, those electrons must go to two separate chlorine atoms. Cl Ca Cl

  11. - Calcium, being an alkaline earth metal, has an oxidation number of +2 Cl 2+ Ca - Cl Chlorine, being a halogen, has an oxidation number of -1

  12. When these two ions combine to form an ionic compound, they will combine in such a way that the overall charge of the compound is zero. In this case, the smallest ratio that adds up to zero is one calcium ion and two chloride ions. - 2+ Ca Cl

  13. When these two ions combine to form an ionic compound, they will combine in such a way that the overall charge of the compound is zero. In this case, the smallest ratio that adds up to zero is one calcium ion and two chloride ions. CaCl2 Note that the metal ion is ALWAYS written first, and that when there is only one ion of an element, it is not necessary to place a subscript “1” next to that element.

  14. Hopefully by this point you can see that it is not necessary to draw out the dot structures before writing the formula for an ionic compound. The dot structures provide us with the oxidation number, and the oxidation numbers determine the ratio of ions in the compound. But since we can find the oxidation numbers of the representative elements from the periodic table, we can skip the step of drawing out the dot structures.

  15. Beryllium and oxygen • Beryllium is an alkaline earth metal and has an oxidation number of +2 (it loses two electrons) • Oxygen has an oxidation number of -2 (it gains two electrons)

  16. Be2+ O2- The smallest ratio that adds up to zero is one beryllium ion to one oxide ion: BeO

  17. Lithium and nitrogen • Lithium is an alkali metal and has an oxidation number of +1 (it loses one electron) • Nitrogen has an oxidation number of -3 (it gains three electrons)

  18. Li+ N3- The smallest ratio that adds up to zero is three lithium ions to one nitride ion: Li3O

  19. Aluminum and sulfur • Aluminum has an oxidation number of +3 (it loses three electrons) • Sulfur has an oxidation number of -2 (it gains two electrons)

  20. Al3+ S2- The smallest ratio that adds up to zero is two aluminum ions to two sulfide ions: Al3S2

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