4.1 Representing Ionic Compounds

Agenda Hand in diagnostic test Lesson 4.1 Representing Ionic Compounds Read pages Vocabulary Learning Check p 142 #1-3 Handout

Learning Goals Students will define the following terms: ionic compound, ion, cation, anion, valence electron, binary ionic compound, polyatomic ion, ternary compound Students will identify cations and anions Students will name ionic compounds Students will write the formula for ionic compounds Students will name compound with multivalent metals. Student will write formulas for compounds with multivalent metals.

Ionic Compounds Elements in the same chemical families form ions with similar ionic charges. Elements in the same group have the same number of valence electrons Valence electrons- the electrons in the outer energy level. Metals and non metals combine to form ionic compounds by transferring electrons from the metal to the non metal. The metal atom loses electrons and becomes positively charged and the non metal gains the electrons and becomes negatively charged.

Ionic compounds are formed when METAL and NON‐METAL elements combine to form a neutral compound. Since electrons are transferred from metals to non‐metals, the opposite charges produce an attraction between the ions. e.g. 1 What is the formula of sodium chloride? Na loses 1 electron to form the Na + ion Na Na + + 1e ‐ Cl gains 1 electron to form the Cl ‐ ion Cl + 1 e ‐ Cl ‐ __________________________________________________________ Na + + Cl ‐ NaCl These are known as ionization equations.

What is the formula of magnesium chloride? Mg loses 2 electrons to form the Mg 2+ ion Mg Mg e ‐ Cl gains 1 electron to form the Cl ‐ ion Cl + 1 e ‐ Cl ‐ __________________________________________________ Mg Cl ‐ MgCl 2 In this case, 2 chloride ions are required to create a neutral compound. The result is a compound that is neutrally charged or the sum of the charges on the positively charged ions equals the sum of the charges on the negatively charged ions

Example: Aluminum chloride Al loses 3 electrons = Al +3 Chorine gains 1 electron = Cl –1 To make the compound electrically neutral we would need 1 aluminum and 3 chloride ions 1 aluminum(+3) + 3 chlorines(-1) = 0

Naming Binary Ionic Compounds A binary ionic compound is a compound made up of a metal cation and a non-metal anion. There are 2 ways to identify a compound 1.By its name 2.By it formula The International Union of Pure and Applied Chemistry (IUPAC) develop rules for naming compounds so that scientists throughout the world can use the same names.

Naming 1. The METAL ion is written first. 2. The NON‐METAL ion is written second with the suffix “‐ide”. Elements in Ionic CompoundName of Ionic Compound Magnesium and phosphorusMagnesium phosphide Sodium and chlorineSodium chloride Calcium and bromineCalcium bromide Aluminum and oxygenAluminum oxide

Writing Formulas For Ionic Compounds The number of electrons that are given up by the metal must equal the number of electrons that are gained by the non-metal. Therefore ionic compounds are neutral and he sum of the positive and negative charges from the ions must equal zero. SymbolGroupElectrons Gained

Steps 1.Identify each ion and its charge. 2. Determine the total positive charge and the total negative charge needed to equal zero. 3.Note the ratio of cations to anions. 4. Use subscripts to show the ratio of ions.

What is the formula for aluminum chloride? 1) Write the symbols, with the metal first AlCl

2) Write the ionic charge above each symbol to indicate the stable ion that each element forms. This information can be found on the periodic table Al Cl

3. Criss cross the charge numbers and use them as subscripts after each element. This balances the charges and makes the compound electrically neutral Al 1 Cl 3 1 Al (+3) and 3 Cl (-1) = 0 1(+3) + 3 (-1) = 0

The Criss-Cross/Cross-Over Rule This rule can be used to easily determine the number of atoms of each element in an ionic compound. By crisscrossing the ionic charge, the number of each atom in the compound is found. * Note that the ionic charges DO NOT appear in the formula! *

Example 1: What is the formula of the ionic compound beryllium nitride?

Multivalent Metals Some transition metals have more than one ionic charge (see Table 1 below). For these, a Roman numeral (I. II, II or IV) is used to indicate the charge. e.g. CuCl 2 is called copper (II) chloride PbF 4 is called lead (IV) fluoride Other transition metals have only one common charge. Silver (Ag) ions are always +1 and zinc (Zn) ions are always +2.

Table 1: Multiple Ionic Charges of Some Metals ElementSymbolIonic ChargesRoman Numeral CopperCu1+ 2+I, II IronFE2+ 3+II, III LeadPb2+ 4+II, IV TinSn2+ 4+II, IV

Naming Ionic Compounds With A Multivalent Metal To name a compound include a Roman numeral to show which charge the ion has. NumberRoman Numeral 1I 2II 3III 4IV 5V 6VI 7VII 8VIII 9IX 10X

Steps 1. Identify the metalCopper (Cu) 2. Verify that the metal is multivalent by looking at the Periodic table. 3. Determine the ratio of the ions in the chemical formula 3 copper : 1 nitride 4. Note the charge of the anion-3 5. The positive and negative charges must balance so that the net or overall charge is zero. Total negative charge -3 Total positive charge Determine what charge the metal ion must have to balance the anion 7. Write the name of the metal ion (include the Roman numeral) The name of the metal ion is copper (I) 8. Write the name of the compoundCopper(1) nitride

Writing the Formula For An Ionic Compound with a Multivalent Metal Use the same steps as for a binary ionic compound. 1.Identify each ion and its charge. 2. Determine the total positive charge and the total negative charge needed to equal zero. 3.Note the ratio of cations to anions. 4. Use subscripts to show the ratio of ions.

What is the formula of tin (II) oxide? +2 ‐2 Using the crisscross rule: Sn O ∴ Chemical Formula: Sn 2 O 2 However. when writing the formula for an ionic compound, always simplify the formula to the lowest common denominator. Therefore the formula is simply SnO since this creates a neutral compound.

Ionic Compounds with Polyatomic Ions Some compounds like calcium carbonate and copper (II) sulphate do not end in “ide” like other ionic compounds. Such compounds are pure substances that involve a metal ion and a polyatomic or complex ion. Polyatomic ions are groups of atoms that tend to stay together and carry an overall charge. E.g. sulphate ion is SO 4 -2 Calcium carbonate contains the carbonate ion. The carbonate ion is a polyatomic ion. Calcium carbonate is composed of calcium, carbon, and oxygen. It is referred to as a ternary compound because it is composed of three different elements.

Common Polyatomic Ions

Writing a Chemical Formula for Polyatomic Ion StepsAluminum Carbonate 1. Using the Periodic table and a table of common polyatomic ions, identify each ion and its charge. 2. Determine the total positive charge and the total negative charge needed to equal zero. 3. Note the ratio of cations to anions2:3 4. Use subscripts to show the ratio of ions. Place the polyatomic ion in brackets if it needs a subscript.

Naming Compounds with Polyatomic Ions The name is simply the name of the metal (use a roman numeral if the metal has more than 1 positive charge) and the name of the polyatomic ion. Both can be found on the periodic table.

Success Criteria I am able to define the following terms: ionic compound, ion, cation, anion, valence electron, binary ionic compound, polyatomic ion, ternary compound I am able to identify cations and anions I am able to name ionic compounds I am able to write the formula for ionic compounds I am able to name compounds with multivalent metals. I am able to write formulas for compounds with multivalent metals.