Ionic Bonds What is an ION? Chapter 2

Ionic Compounds 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 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

Oxidation States Some typical rules that are used for assigning oxidation states of simple compounds follow: FluorineFluorine has an oxidation state of −1 in all its compounds, since it has the highest electronegativity of all reactive elements.electronegativity HydrogenHydrogen has an oxidation state of +1 except when bonded to more electropositive elements such as sodium, aluminium, and boron, as in NaH, NaBH 4, LiAlH 4, where each H has an oxidation state of -1.oxidationsodiumaluminiumboron NaHNaBH 4LiAlH 4 OxygenOxygen 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, OF 2,+1 in O 2 F 2.peroxidessuperoxidesozonidesoxygen difluoride Alkali metalsAlkali metals have an oxidation state of +1 in virtually all of their compounds (exception, see alkalide).alkalide Alkaline earth metalsAlkaline earth metals have an oxidation state of +2 in virtually all of their compounds. HalogensHalogens, other than fluorine have an oxidation state of −1 except when they are bonded to oxygen, nitrogen or with another halogen.

Ionic Bonds 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 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?

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)

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 CaF 2

IONIC Bonds Polyatomic Ions – an ion made of more than one atom CO 3 (Carbonate) SO 4 (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

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 801 o C Conduct electricity Dissolve in water Ions become more loosely associated Pass electrical charges along

Review Questions 4. Name these compounds: NaF, BeI 2, K 2 SO 4, CaO, H 2 S, MgCO 3 Sodium fluoride Berylium Iodide Potassium Sulfate Calcium Oxide Hydrogen Sulfide Magnesium Carbonate

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

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

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 moleculesLewis structure second one is used for simple compounds (molecular or not) and does not require a Lewis structure.

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

Formula Names Examples Sodium (Na + ) and Chlorine (Cl - ) NaCl = ratio 1:1 Sodium Chloride Calcium (Ca2+) and Fluorine (Fl-) CaFl 2 = 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 Al 2 S 3 Aluminum Sulfide

Formulas with Polyatomic Ions Poly atomic ions stay together as a single group Example Calcium and Phosphate Calcium (2+) Phosphate PO 4 (3-) 3 (Ca) + 2 ( PO 4 ) Ca 3 (PO 4 ) 2 Calcium Phosphate

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

Naming Review 1. Name cation first, anion second 2. Monatomic ions use atom name 3. Monatomic anions take root of name and add –ide suffix 4. Group 1A and 2A metals have only one oxidation state. Transition metals can have more than one. Put oxidation state in as roman numerals 5. Polyatomic ions – just name the ion

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’ Fe 2 O 3 (ferrous oxide) – larger oxidation state is ‘-ous’ New Naming Convention FeO – Iron (II) Oxide – (II) indicates oxidation state Fe 2 O 3 – Iron (III) Oxide