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Chemistry II

Chemistry II. Ionic Compounds Naming and Writing Formulas. Review of how ions are formed. Octet rule – elements are most stable when they have 8 valence electrons Elements can gain or lose valence electrons in order to have 8. sodium ion Na +. e -. e -. e -. e -. 11 p +. e -. e -.

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Chemistry II

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  1. Chemistry II Ionic Compounds Naming and Writing Formulas

  2. Review of how ions are formed • Octet rule – elements are most stable when they have 8 valence electrons • Elements can gain or lose valence electrons in order to have 8.

  3. sodium ion Na+ e- e- e- e- 11p+ e- e- e- e- e- e- Formation of Cation sodium atom Na e- e- e- e- e- e- loss of one valence electron 11p+ e- e- e- e- e- e-

  4. chloride ion Cl1- e- e- e- e- e- e- e- e- 17p+ e- e- e- e- e- e- e- e- e- e- Formation of Anion chlorine atom Cl gain of one valence electron e- e- e- e- e- e- e- e- 17p+ e- e- e- e- e- e- e- e- e- e-

  5. Bonding • Chemical Bond • attractive force between atoms or ions that binds them together as a unit • Purpose bonds formFORM IN ORDER TO …. • To decrease potential energy (PE) • To Increase stability Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  6. Why bonds form… • Atoms of many elements are more stable as they are bonded to other atoms. • Energy is released into surroundings resulting in a system with lower energy. • An atom’s electron configuration determines how it interacts with other atoms • Particularly valence electrons

  7. What are ionic bonds? • Chemical interactions(attractions) between charged particles - Called Electrostatic attraction • Result from a transfer of electrons making a cation and anion

  8. Crystal Lattice NaCl 1:1 Ratio Ionic compounds do not exist as single molecules but rather as numerous units organized in a stable crystal .

  9. Participants • Ionic bonds form between metals and non-metals • Metals have lower ionization energies and therefore more readily “give away” electrons – Form Cations • Non-metals have high electron affinities and therefore more readily accept electrons. – Form Anions • New Term- Oxidation Number = ion charge • sodium’s oxidation number is 1+, Chlorine’s is 1-

  10. Naming Ionic Compounds • Cation – borrows name from element • Always listed first • Anion – ends in “ide” (with the exception of polyatomic ions) • Always listed second • Examples • NaCl – sodium chloride • ZnS – zinc sulfide • Mg3N2 – magnesium nitride • SPELLING COUNTS!

  11. Step 3: AlCl 3 Writing Ionic Formulas Criss-Cross Rule Example: Aluminum Chloride Step 1: Write symbols & charge of elements. Write charges ABOVE the letters 1- Al Cl 3+ Step 2: Al Cl 1 3 criss-cross charges as subscripts combine as formula unit *“1” is never shown *get rid of charges on top Step 4 : *simplify if needed

  12. Variable Charge Ions • Some elements in the transition metals can form more than one type of ion. Sometimes they may lose 2, 3, 4 or even more electrons in order to bond with another element. • So these metals can form +2, +3 ,+4 etccationsin one compound but have a different charge in another compound. In order to tell them apart we name them differently.

  13. Writing the formula • When given the name of the compound, the Roman numeral after the metal tells us the CHARGE of the metal. • Copper II Chloride – means Cu+2 Cl-1 • Follow the same steps as before >>>> 1. Write out the charges 2. Criss-cross 3. Combine as a formula unit (get rid of charges on top) 4. Simplify if needed

  14. Cu Fe A. To name, given the formula: • Figure out charge on • cation. 2. Write name of cation. 3. Write Roman numerals in ( ) to show cation’s charge. Stock System of nomenclature 4. Write name of anion. iron oxide Fe2+ Fe? iron (II)oxide FeO O2– iron oxide Fe? O2– Fe2O3 Fe? Fe3+ O2– O2– Fe3+ iron (III)oxide CuBr copper bromide Cu? Br1– copper (I)bromide Cu1+ CuBr2 copper bromide Br1– copper (II)bromide Cu2+ Cu? Br1–

  15. When writing the formula for an ionic compound with a polyatomic ion, follow the same rules but treat the polyatomic ion as a single unit.

  16. Writing Formulas w/Polyatomic Ions Polyatomic Ion: a group of atoms that stay together and have a single, overall charge. BaSO4 barium sulfate Ba2+ and SO42– Mg(NO2)2 Mg2+ and NO21– magnesium nitrite NH4ClO3 ammonium chlorate NH41+ and ClO31– Sn(SO4)2 tin (IV) sulfate Sn4+ and SO42– ? Fe2(Cr2O7)3 Fe3+ and Cr2O72– iron (III) dichromate ammonium nitride (NH4)3N NH41+ and N3–

  17. 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 of that in the formula. Examples: NaNO3 NO31-, but there is only one of it. Co(NO3)2NO31- there are two of them (NH4)2SO4NH41+there are two of them; SO42-there is only one of it. Co(OH)2 OH1-there are two of it. Al2(CO3)3 CO32-there are three of them. NaOH OH1-there is only one of it.

  18. Pattern to Memorizing Nomenclature XY “-ide” XYO4 XYO3 XYO2 XYO “per___-ate” “-ate” “-ite” “hypo___-ite” 1 more oxygen normal 1 less oxygen 2 less oxygen

  19. Physical Characteristics • Physical characteristics result from the strong attractive forces between charged particles and the crystal structure • High melting and boiling points • Lots of energy necessary to break strong bonds • Solid at room temperature • Stable crystal structure • Hard and brittle • Crystal allows compound to withstand great force • Too much force causes repulsive forces to overpower attractive forces and the crystal shatters • Conduct electricity when melted and dissolved in water • Charged particles that are able to move

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