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Ionic Compounds

Ionic Compounds. Unit 6. Writing Formulas. Elements occur in constant whole number ratios in a compound (Law of Definite Proportions). In a chemical formula symbols and subscripts are used to describe this ratio.

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Ionic Compounds

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  1. Ionic Compounds Unit 6

  2. Writing Formulas • Elements occur in constant whole number ratios in a compound (Law of Definite Proportions). • In a chemical formula symbols and subscripts are used to describe this ratio. • For molecules the chemical (molecular) formula shows the actual number of atoms of each element in the compound • In an ionic compound, the formula shows the lowest whole number ratio of elements in the ionic crystal. • This ratio is called a formula unit.

  3. Identifying Ionic Compounds • Any substance made of metal cation and nonmetal anion OR contains any polyatomic ions • Ionic bond = transfer of electrons • 1 atom loses, 1 atom gains (cation/anion formed) • the + and – particles are attracted to one anther and form a very stable bond (electrostatic attract.) • Properties of ionic compounds: • high melting point • low malleability – break and shatter easily • can conduct electricity under certain conditions • Coordination number – the number of ions of opposite charge that surround the ion in a crystal

  4. Accessed 11-30-09 http://images.google.com/imgres?imgurl=http://www.everyscience.com/Chemistry/Inorganic/Ionic_Solids/.images/ni6as.gif&imgrefurl =http://www.everyscience.com/Chemistry/Inorganic/Ionic_Solids/b.1297.php&usg=__agLG82xXC9Yj5oqyhykNAtqKDKc=&h=480&w=640&sz=8&hl=en&start =14&um=1&itbs=1&tbnid=R3WSQd3Jddh8JM:&tbnh=103&tbnw=137&prev=/images%3Fq%3Dcoordination%2Bnumber%2Bof%2Bionic%2B compounds%26hl%3Den%26safe%3Dactive%26rlz%3D1T4EGLC_enUS321US342%26um%3D1

  5. Naming Ionic Compounds • Simply name the two ions, positive ion first (the positive ion is always first). • Positive monatomic (one type of element) ions have the same name as the element. • Na+ sodium ion • Al3+ aluminum ion

  6. Naming Ionic Compounds • Negative monatomic ions end in –ide. • Cl- chloride ion • O2- oxide ion • Negative polyatomic ions end in –ate or –ite. • There is not a hard and fast rule which will allow you to determine if a polyatomic ion is –ate or –ite (which is why you have to memorize them), but there is one helpful shortcut.

  7. Patterns for Polyatomic Ions • The most common form of a polyatomic ion formed from a nonmetal combined with oxygen ends in –ate. • -ate ion • chlorate = ClO3- • -ate ion plus 1 O Þ same charge, per- prefix • perchlorate = ClO4- • -ate ion minus 1 O Þ same charge, -ite suffix • chlorite = ClO2- • -ate ion minus 2 O Þ same charge, hypo- prefix, -ite suffix • hypochlorite = ClO-

  8. Patterns for Polyatomic Ions • If the polyatomic ion starts with H, add hydrogen- before the ions name and add 1 to the charge CO32- = carbonate \ HCO3- = hydrogen carbonate

  9. Writing Ionic Formulas • IMPORTANT – When writing formulas, use appropriate subscripts so the total number of positive and negative charges cancel out and the compound is neutral. • Now, lets see how good we are at writing some formulas and naming some ionic compounds.

  10. Practice • KBr • Since this has a metal (K) and a nonmetal (Br), we say it is an ionic compound. • So we name the positive ion – potassium and the negative ion with the ending changed to –ide, bromide. • Potassium bromide

  11. Practice • Calcium Chloride • Again a metal and a nonmetal so it is ionic. • Calcium would form an ion with a 2+ charge • and chloride would be 1-. • Ca2+Cl- in order for the compound to be neutral, how many Cl- would there need to be for every Ca2+?? • 2 Cl- for every 1 Ca2+ • So the formula would be CaCl2

  12. Practice • Na2CO3 • In this compound there are two ways to identify is as ionic. • First, it has a metal and a nonmetal. • Second, it has a polyatomic ion. • So we name the ions, positive ion first. • Sodium carbonate

  13. Practice • Magnesium Phosphate • magnesium – Mg2+ ; phosphate – PO43- • In order for the compound to be neutral we have to find the least common multiple between our two charges, 2 and 3. The LCM is 6. • 2 goes into 6 – 3 times so Mg3; 3 goes into 6 – 2 times so (PO4)2. • 3 x +2 = +6 AND 2 x -3 = -6 • Our compound is neutral. • Mg3(PO4)2

  14. Important Precautions • If we need more than one polyatomic ion (like in the previous example), it must be surrounded by parentheses before you add the subscript. • Also, notice that if the subscript is 1 we do not write it. • If the positive ion has more than one possible oxidation number, then when we write the name we must indicate which oxidation state it is. • This is done by writing a roman numeral in parentheses which is equal to the positive charge.

  15. Practice • Copper (I) Oxide • (I) indicates that the copper has a charge of 1+. • Copper - Cu1+ ; oxide – O2- • Cu2O • Iron (III) Oxide • (III) indicates iron has a 3+ charge. • Iron - Fe3+ ; Oxide – O2- • Fe2O3 Practice and More Practice!!!

  16. Naming Hydrates • Hydrates are crystalline compounds which attract and hold water molecules. • The water is called the water of hydration and can be removed (evaporated) by heating. • After water is removed the crystal is said to be anhydrous.

  17. Naming Hydrates • To name hydrates simply name the compound (usually ionic) and then indicate the number of water molecules by using the same prefixes as in molecular compounds. • CuSO4• 5 H2O • Copper (II) sulfate pentahydrate • Sodium carbonate heptahydrate • Na2CO3 • 7 H2O

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