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Unit 5

Unit 5. Ionic Bonding. Pure Substances & Nomenclature. Pure substances can exist in several forms: I) Atomic Elements & Molecular Elements, II) Ionic Compounds and III) Molecular Compounds (studied in next unit)

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Unit 5

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  1. Unit 5 Ionic Bonding

  2. Pure Substances & Nomenclature • Pure substances can exist in several forms: I) Atomic Elements & Molecular Elements, II) Ionic Compounds and III) Molecular Compounds (studied in next unit) I. - Atomic Elements & Molecular Elements: Some elements can exist as single atoms such as He, Ne, Cu, Hg, Au, Pb, U - Molecular Elements: Some elements exist in nature as diatomic molecules: H2 N2 O2 F2 Cl2 Br2 I2 • Know these • Their names are the same as the element names Two elements are commonly polyatomic. Sulfur S8 Phosphorous P4

  3. II. Ionic Compounds II. Ionic Compounds: These are compounds formed between ions. • The metal loses electrons to become a + ion (Cation), and the nonmetal gains electrons to become a – ion (Anion). • The + and – ions are attracted to each other in a ratio so that the resulting compound is neutral in charge; NaCl MgF2 are examples. • The formula unit is the simplest ratio of ions • These have unique names formed from naming the + ion followed by the – ion with an “ide” ending.

  4. “Perhaps one of you gentlemen would mind telling me just what is outside the window that you find so attractive..?” Image courtesy NearingZero.net

  5. Valence electrons • Are electrons in highest occupied energy level of an atom. • For representative elements, number of valence electrons is the same as its group number. • Ex. Lithium is in group 1A: has 1 valence electron • Some transition metals form more than one ion. • Ex. Fe2+ and Fe3+ • Octet rule: atoms tend to achieve the electron configuration of a noble gas (8 electrons in outer energy level)by gaining or losing electrons.

  6. elements of Group 6A have a -2 charge elements of Group 5A have a-3 charge elements of Group 2A have a+2 charge elements of Group 7A have a-1 charge Elements in Group 1A have a +1 charge The charge on an ion can be predicted from its position in the periodic table.

  7. If one or more electrons are removed from a neutral atom a positive ion is formed. A positive ion is called a cation. remove e- → neutral atom cation

  8. Naming Cations Cations are named the same as their parent atoms.

  9. If one or more electrons are added to a neutral atom a negative ion is formed. A negative ion is called an anion. add e- → neutral atom anion

  10. An anion consisting of one element has the stem of the parent element and an –ideending Naming Anions

  11. fluorine (F) F- stem fluoride ion AtomAnionName of Anion

  12. chlorine (Cl) Cl- stem Chlorideion AtomAnionName of Anion

  13. stem bromine (Br) AtomAnionName of Anion Br- bromideion

  14. stem nitrogen (N) AtomAnionName of Anion N3- nitrideion

  15. stem phosphorous (P) AtomAnionName of Anion P3- phosphide ion

  16. stem oxygen (O) AtomAnionName of Anion O2- oxideion

  17. Writing Formulas FromNames of Ionic Compounds A chemical compound must have anet charge of zero. If the compound contains ions, then the charges on all of the ions must add to zero.

  18. Step 4: AlCl 3 Criss-Cross Method Example: Aluminum Chloride Aluminum Chloride Step 1: write out name with space Al Cl 3+ 1- Step 2: write symbols & value of charge of ions Al Cl Step 3: 1 3 criss-cross charges as subsrcipts combine as formula unit (“1” is never shown)

  19. Criss-Cross Rule Example: Aluminum Oxide Step 1: Aluminum Oxide Step 2: Al3+ O2- Step 3: Al O 2 3 Step 4: Al2O3

  20. Criss-Cross Rule Example: Magnesium Oxide Step 1: Magnesium Oxide Step 2: Mg2+ O2- Step 3: Mg O 2 2 Step 4: Mg2O2 Step 5: MgO Use simplest ratios

  21. Naming ionic compounds To name an ionic compound first write the name of the cation (+ ion) followed by the name of the anion (- ion)

  22. Naming Binary Compounds Formula Name barium oxide • BaO ____________________ • ________________ sodium bromide • MgI2 ____________________ • KCl ____________________ • ________________ strontium fluoride • ________________ cesium fluoride NaBr magnesium iodide potassium chloride SrF2 CsF

  23. Classwork: handout ionic binary compounds (single charge cations.)

  24. Naming Compounds Containing Polyatomic Ions A polyatomic ion is an ion that contains two or more elements.

  25. superscripts SO42- Al3+ Al2(SO4 )3 subscripts ALUMINUM SULFATE

  26. Rules for Parentheses Parentheses are used only when the following two condition are met: • There is a polyatomic ion present and… • There are two or more polyatomic ions in the formula. Examples: NaNO3NO31- is a polyatomic ion, but there is only one of it. Co(NO3)2NO31-is a polyatomic ion and there are two of them (NH4)2SO4NH41+is a polyatomic ion and there are two of them; SO42-is a polyatomic ion but there is only one of it.

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