IONIC COMPOUNDS

Formation of Ions Many of the properties of the elements are due to their valence electrons. These same electrons are involved in the formation of chemical bonds between two atoms. Electron dot structures help keep track of the valence electrons.

Formation of Ions Remember from last unit that ionization energy refers to the energy required to remove an electron from an atom – the lower the energy, the easier it is to remove the electron. Another property, electron affinity, refers to how much attraction a neutral atom has for a free electrons. When an electron is added to an atom having high electron affinity, energy is released.

Formation of Ions The nonmetals have high electron affinity, while the metals have low electron affinity. This is because nonmetals want to gain electrons while metals want to lose electrons. Elements gain, lose, or share valence electrons so their valence shell mimics that of a noble gas. Noble gases have a full outermost energy level (valence shell) ns 2 np 6 which gives them a stable octet.

Positive Ions A positive ions forms when an atom loses one or more electrons: ATOM + Ionization Energy → ION + + e - A positive ion is called a cation. Losing electrons will give the resulting cation an electron configuration similar to that of a noble gas. But, it does not change the element into a noble gas.

Positive Ions The reactivity of metals is based on the ease with which they lose valence electrons. Group 1: ns 1 lose 1 e - Group 2: ns 2 lose 2 e - Group 3: ns 2 (n-1)d 1 lose 3 e - (from s & d) Group 13: ns 2 np 1 or ns 2 (n-1)d 10 np 1 lose 3e - (from s & p) Group 14: ns 2 np 2 or ns 2 (n-1)d 10 np 2 lose 4e - (from s & p) The transition elements lose electrons in a variety of ways from both the s and d orbitals. This gives them a wide variety of positively charged cations.

Negative Ions A negative ion forms when an atom gains one or more electrons. ATOM + e - → ION - + energy Nonmetals have a great attraction for electrons and form a stable octet by gaining electrons. A negative ion is called an anion.

Negative Ions Nonmetals form anions as follows: Group 14: ns 2 np 2 or ns 2 (n-1)d 10 np 2 (gain 4e - in p) Group 15: ns 2 np 3 or ns 2 (n-1)d 10 np 3 (gain 3e - in p) Group 16: ns 2 np 4 or ns 2 (n-1)d 10 np 4 (gain 2e - in p) Group 17: ns 2 np 5 or ns 2 (n-1)d 10 np 5 (gain 1e - in p)

Ionic Bonds Oppositely charge ions attract one another. The electrostatic forces that hold oppositely charged particles together in a compound are called an ionic bond. Any compound formed in this manner is called an ionic compound. Ionic compounds have no resultant charge – they are neutral.

Ionic Bonds The process for sodium chloride (NaCl) looks like: st=PLRIs-O4v9NBjq8gz8OiF9GrZtECtQ_tbv&index=2 st=PLRIs-O4v9NBjq8gz8OiF9GrZtECtQ_tbv&index=2

Properties of Ionic Compounds The chemical bonds that occur between the atoms in a compound determine many of the physical and chemical properties of the compound. In an ionic compound, the positive and negative ions are packed into a regular repeating pattern that balances the forces of attraction and repulsion. This particle packing forms an ionic crystal:

Properties of Ionic Compounds The three-dimensional crystal lattice gives the crystal its shape and properties. Ionic compounds are: very strong rigid have high melting points have high boiling points require a large amount of energy to be decomposed

Names & Formulas for Ionic Compounds Since the generic term “salt” can mean any one of thousands of chemical compounds, a better system is needed to describe an ionic compound. The system used is based on the chemical symbols on the periodic table and was developed by a German chemist in 1919 named Alfred Stock.

Monatomic Ions A monatomic ion is either a cation or an anion formed from a single atom. To write the chemical symbol for a monatomic ion you must write both the element’s symbol and the charge of the ion.

Example Write the symbol for the ions formed from: Cesium Cs + Beryllium Be 2+ or Be +2 Aluminum Al 3+ or Al +3 Fluorine F - Oxygen O 2- or O -2

Monatomic Ions The charge of a monatomic ion is also called its oxidation number, or oxidation state. Groups 1, 2, 3, 13 – 18 generally have one oxidation number while the transition elements typically have more than one. Some elements have both positive and negative oxidation numbers. The oxidation state used will depend on the other elements bonding with it.

Monatomic Ions The oxidation number of an element in an ionic compound equals the number of electrons transferred from one atom and accepted by another atom. The nomenclature for monatomic cations is fairly simple. A monatomic cation is named using the name of the element followed by the word ion. The word ion must be included in the name of the ion in order for it to be correct.

Monatomic Ions Na + Sodium ion Al 3+ Aluminum ion

Monatomic Ions A monatomic anion is named by dropping the ending of the element’s name and adding the suffix –ide, followed by the word ion. C l - Chloride ion O 2- Oxide ion N 3- Nitride ion

Example Name the following ions: H + hydrogen ion S 2- sulfide ion H - hydride ion Sr 2+ strontium ion P 3- phosphide ion

Nomenclature for Ions with Multiple Charges The transition elements form many different cations depending upon the number of electrons they give up. To distinguish between the various charges, Roman numerals are used to represent the number of electrons given up – in other words – the charge: 1 – I5 – V 2 – II6 – VI 3 – III7 - VII 4 - IV

Nomenclature for Ions with Multiple Charges Roman numerals are used only when naming cations that have more than one positive charge from which to choose. To do otherwise is WRONG !! Anions, even though they may have more than one negative charge, NEVER use Roman numerals.

Nomenclature for Ions with Multiple Charges The naming process is: Write the name of the element Next write the appropriate Roman numeral enclosed inside a set of parentheses Write the word “ion”

Example Name the following ions: Fe 2+ Iron (II) ion Cr 3+ Chromium (III) ion V 5+ Vanadium (V) ion Mo 7+ Molybdenum (VII) ion Zn 2+ Zinc ion

Writing Formulas for Ionic Compounds An ionic compound is neutral even though it is composed of charged ions. Steps for writing a chemical formula: barium sulfide List the cation and its charge Ba 2+ List the symbol for the anion and its charge S 2-

Writing Formulas for Ionic Compounds Write the symbols for the ions side-by-side, with the cation first Ba 2+ S 2- If the charges don’t balance criss-cross them BaS The charge number – no sign – becomes the subscript for the cation or anion.

Writing Formulas for Ionic Compounds molybdenum (V) oxide Mo 5+ O 2- Mo 5+ O 2- Mo 2 O 5 The chemical formula represents the compound’s composition.

Examples: Determine the formula for each of the following ionic compounds: aluminum nitride A l N strontium phosphide Sr 3 P 2 calcium chloride CaC l 2 tin (IV) fluoride SnF 4

Examples: rubidium iodide RbI iron (II) oxide FeO aluminum oxide A l 2 O 3 copper (II) arsenide Cu 3 As 2

Naming Ionic Compounds Ionic compounds consisting of two ions, cation and anion, are known as binary compounds. To name an ionic compound: Name the cation first If the cation has multiple positive charges, include the Roman numeral inside a set of parentheses Name the anion second

Naming Ionic Compounds Cations with variable oxidation states: Cu: +1, +2Ti: +2, +3, +4 Au: +1, +3Cr: +2, +3, +6 Co: +2, +3Mn: +2, +3, +4, +7 Fe: +2, +3 Ni: +2, +3 Pb: +2, +4 Pt: +2, +4 Sn: +2, +4

Naming Ionic Compounds Example: Rb 2 Se rubidium selenide rubidium selenide

Naming Ionic Compounds Example: Pb 3 N 4 lead (IV) nitride lead (IV) nitride

Examples Name the following ionic compounds: MgBr 2 magnesium bromide A l 2 S 3 aluminum sulfide MnCl 4 manganese (IV) chloride VI 3 vanadium (III) iodide

Examples Ni 2 O 3 nickel (III) oxide BeO beryllium oxide YN yttrium nitride CrO 3 chromium (VI) oxide

Polyatomic Ions A polyatomic ion is an ion made up of two or more atoms bonded together that functions as a single ion. Polyatomic ions have special names that must be memorized. Polyatomic ions can be either cations or anions. Ionic compounds containing polyatomic ions must be neutral.

Polyatomic Ions Polyatomic ions have charges just like monatomic ions. The charge sign is written to the right of the ion’s formula and it applies to the entire ion. Parentheses are used to group polyatomic ions when more than one is used in the compound. A subscript outside the parentheses indicates the number of polyatomic ions used. Ca(OH) 2

Polyatomic Ions Memorize the following polyatomic ion names and symbols, including the charges. NH 4 + ammonium ionOH - hydroxide ion NO 2 - nitrite ionPO 4 3- phosphate ion NO 3 - nitrate ionC l O - hypochlorite ion SO 3 2- sulfite ionC l O 2 - chlorite ion SO 4 2- sulfate ionC l O 3 - chlorate ion CO 3 2- carbonate ionC l O 4 - perchlorate ion HCO 3 - bicarbonate ionCrO 4 2- chromate ion C 2 H 3 O 2 - acetate ionMnO 4 - permanganate ion CN - cyanide ionO 2 2- peroxide ion

Compounds with Polyatomic Ions Ionic compounds containing polyatomic ions are named in the same manner as binary ionic compounds. The cation is first and the anion is second. Formulas for ionic compounds containing polyatomic ions are written in the same manner as binary ionic compounds. The cation formula is written first and the anion formula is written second.

Compounds with Polyatomic Ions Special notes for formula writing: When more than one polyatomic ion is used in a formula, enclose it inside a set of parentheses and then add the subscript outside the parentheses. Ca(OH) 2 Parentheses are NOT to be used if only one polyatomic ion is used in the formula.

Example Write the formula for: strontium perchlorate Sr 2+ ClO 4 - Sr(C l O 4 ) 2

Examples: Write the formula for each of the following compounds: aluminum sulfate A l 2 (SO 4 ) 3 magnesium hydroxide Mg(OH) 2 copper (II) acetate Cu(C 2 H 3 O 2 ) 2 copper (I) phosphate Cu 3 PO 4

Examples: Write the formula for each of the following compounds: sodium bicarbonate NaHCO 3 hydrogen peroxide H 2 O 2 ammonium hydroxide NH 4 OH

Naming Name the following compounds: NaNO 3 sodium nitrate Fe(OH) 3 iron (III) hydroxide (NH 4 ) 2 SO 4 ammonium sulfate Cu 3 (PO 4 ) 2 copper (II) phosphate