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Ionic Bonds What is an ION?

Ionic Bonds What is an ION?. Chapter 2. How are positive ions formed?. Atom loses one or more VALENCE electrons Called a CATION Ion becomes more stable by losing electrons (octet rule) Not a change in atom, Just an ion Loses all electrons in outer shell

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Ionic Bonds What is an ION?

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  1. Ionic BondsWhat is an ION? Chapter 2

  2. How are positive ions formed? Atom loses one or more VALENCE electrons Called a CATION Ion becomes more stable by losing electrons (octet rule) Not a change in atom, Just an ion Loses all electrons in outer shell Reactivity depends on ease of losing electrons Transition metals usually form 2+ or 3+ ions shown with a (II) or (III) Ionic Compounds

  3. How are positive ions formed? Group 1A loses 1 valence electron Group 2A loses 2 valence electrons Group 3A (13) loses 3 valence electrons Group 4A (14) does not generally make ionic compounds Ionic Compounds

  4. Oxidation States • Some typical rules that are used for assigning oxidation states of simple compounds follow: • Fluorine has an oxidation state of −1 in all its compounds, since it has the highest electronegativity of all reactive elements. • Hydrogen has an oxidation state of +1 except when bonded to more electropositive elements such as sodium, aluminium, and boron, as in NaH, NaBH4, LiAlH4, where each H has an oxidation state of -1. • Oxygen has an oxidation state of −2 except where it is −1 in peroxides, −1/2 in superoxides, −1/3 in ozonides, and of +2 in oxygen difluoride, OF2,+1 in O2F2. • Alkali metals have an oxidation state of +1 in virtually all of their compounds (exception, see alkalide). • Alkaline earth metals have an oxidation state of +2 in virtually all of their compounds. • Halogens, other than fluorine have an oxidation state of −1 except when they are bonded to oxygen, nitrogen or with another halogen.

  5. How do negative ions form? Atoms gain negative electrons Nonmetals have a great attraction for electrons Adding electron fills up the shell = stable Called an ANION Naming: change name to end in –ide Gaining enough electrons to fill outer shell (octet rule) 7A gains 1 6A gains 2 5A gains 3 Ionic Bonds

  6. Ionic Compounds • Ionic compounds are Metal+ and Nonmetal- • Metals make Cations • Groups 1A (1) – 3A (13) and all Group D elements • Form + ions • Nonmetals make Anions • Group 5A (15) - 7A (17) • Nobel Gasses (Group 8A/18) do not form compounds. Why?

  7. Ionic Bonds • Ions – Atom or group of atoms that has become electrically charged • Negative ion (-) – gains extra electron • Positive ion (+) – loses an electron • Forming IONs depends upon Valence Electrons • Sodium has ONE Valence Electron (wants to give one away to have full electron shell) • Chlorine has SEVEN Valence Electrons (wants to TAKE one electron to have full electron shell)

  8. Ionic Bonds • The number of electrons lost by the Cation MUST EQUAL the number of electrons gained by the Anion. • Calcium makes a 2+ cation • Fluorine makes a 1- anion • Therefore it takes 2 fluorine atoms to combine with one calcium atom to create calcium fluoride • Chemical formula is CaF2

  9. IONIC Bonds • Polyatomic Ions – an ion made of more than one atom • CO3 (Carbonate) • SO4 (Sulfate) • Naming Ionic Compounds • Name of positive ion comes first • Name of negative ion comes second, plus –ide • Example: NaCl = sodium chloride, • Example: KI = potassium iodide

  10. Properties of Ionic Compounds • Crystal shape • Alternate positive and negative ions in patterns • Crystals are all the same shape for each compound • High melting points • Table Salt Melting point is 801oC • Conduct electricity • Dissolve in water • Ions become more loosely associated • Pass electrical charges along

  11. Review Questions • Name these compounds: NaF, BeI2, K2SO4, CaO, H2S, MgCO3 • Sodium fluoride • Berylium Iodide • Potassium Sulfate • Calcium Oxide • Hydrogen Sulfide • Magnesium Carbonate

  12. Formulas • Formula unit is the ratio of cations to anions’ • Total number of electrons lost by cations must equal total number of electrons gained by anions • Binary compounds = simplest compound = 2 atoms • One cation, one anion • Monatomic ion = ion made from one atom

  13. Typical Ions • Oxidation number = oxidation state = number of electrons transferred from an atom to make a compound • Na+ oxidation number = +1 • O2- oxidation number = 2- • Used to determine compound formulas

  14. Oxidation States • "Oxidation state :A measure of the degree of oxidation of an atom in a substance. It is defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules: • (l) the oxidation state of a free element (uncombined element) is zero; • (2) for a simple (monatomic) ion, the oxidation state is equal to the net charge on the ion; • (3) hydrogen has an oxidation state of 1 and oxygen has an oxidation state of -2 when they are present in most compounds. • There are two common ways of computing the oxidation state of an atom in a compound. • The first one is used for molecules when one has a Lewis structure, as is often the case for organic molecules • second one is used for simple compounds (molecular or not) and does not require a Lewis structure.

  15. Formula Names • Remember: total number of electrons lost by cations must equal total number of electrons gained by anions! • Metal name is stated first. • Number of cations in ratio is subcripted • Nonmetal name is stated second • Suffix –ide is used • Number of anions in ration is subscripted

  16. Formula Names • Examples • Sodium (Na+) and Chlorine (Cl-) NaCl = ratio 1:1 Sodium Chloride • Calcium (Ca2+) and Fluorine (Fl-) CaFl2 = ratio 1:2 Calcium Fluoride Aluminum (3+) and Sulfur (2-) Find lowest common dominator (6) 2(Al 3+) + 3 (S 2+) = both transfer 6 electrons Al2S3 Aluminum Sulfide

  17. Formulas with Polyatomic Ions • Poly atomic ions stay together as a single group • Example Calcium and Phosphate • Calcium (2+) • Phosphate PO4 (3-) • 3 (Ca) + 2 ( PO4) • Ca3(PO4)2 • Calcium Phosphate

  18. Naming Polyatomic Compounds • Oxyanions = polyatomic anions with one or more oxygen atom • With 2 anion forms: • Anion with most oxygen atoms is –ate • Anion with fewer oxygen atoms is –ite • With multiple anion forms: • Most oxygen atoms is per- metal -ate • Second most oxygen is –ate • Third most oxygen atoms is –ite • Fourth most oxygen atoms is hypo- metal -ite

  19. Naming Review • Name cation first, anion second • Monatomic ions use atom name • Monatomic anions take root of name and add –ide suffix • Group 1A and 2A metals have only one oxidation state. Transition metals can have more than one. Put oxidation state in as roman numerals • Polyatomic ions – just name the ion

  20. Naming Transition Element Compounds • Iron can exist as either +2 or +3 oxidation state. How do we know the difference? • Old Naming Convention • FeO (ferric oxide) – lowest oxidation state is ‘-ic’ • Fe2O3 (ferrous oxide) – larger oxidation state is ‘-ous’ • New Naming Convention • FeO – Iron (II) Oxide – (II) indicates oxidation state • Fe2O3 – Iron (III) Oxide

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