WRITING AND NAMING IONIC COMPOUNDS

When atoms combine, it’s always in simple whole number ratios The smallest unit of atomic combinations that retains the characteristics of the compound is a molecule

The composition of a molecule can be represented in two ways as either an empirical formula or a molecular formula CH2 C3H6 An empirical formula gives the simplest ratio of atoms in a compound A molecular formula tells how many of each atom are present in the compound

A remarkable feature of compounds formed from elements is that the properties of the reactant elements are lost. +

In order to become more stable an some atoms find it energetically fea-sible to either lose or gain valence electrons. Atoms that lose e- are positive A.K.A. cation Atoms that gain e- are negative A.K.A. anion

We tend to focus specifically on the loss or gain of the outer s, p, (A.K.A. valence e-) ,and sometimes the d e- of unfilled d sublevels). The valence e- an atom contains has a direct effect on the charge the atom develops as it forms an ionic bond. We have a list of the common ionic charges developed during ionic bonding.

MONATOMIC IONS +1 SOME COMMON CATIONS Lithium +1 SOME COMMON CATIONS (Note: the names of many of the ions include Roman numerals. These numerals are known as the Stock system of naming chemical ions and elements) +2 +3 +4 Li+1 Magnesium Mg+2 Aluminum Al+3 Lead (IV) Pb+4 Sodium Na+1 Calcium Ca+2 Chromium(III) Cr+3 Vanadium (IV) V+4 Potassium K+1 Strontium Sr+2 Iron (III) Fe+3 Tin (IV) Sn+4 Rubidium Rb+1 Barium Ba+2 Vanadium (III) V+3 Cesium Cs+1 Cadmium Cd+2 Copper (I) Cu+1 Chromium (II) Cr+2 Silver Ag+1 Cobalt Co+2 Copper (II) Cu+2 Iron (II) Fe+2

MONATOMIC IONS SOME COMMON CATIONS (Note: the names of many of the ions include Roman numerals. These numerals are known as the Stock system of naming chemical ions and elements) +1 +2 +3 +4 Lead (II) Pb+2 Manganese (II) Mn+2 MONATOMIC IONS Mercury (II) Hg+2 Nickel (II) Ni+2 Tin (II) Sn+2 Vanadium (II) V+2 Zinc Zn+2

MONATOMIC IONS SOME COMMON ANIONS (Note: the names of many of the ions include Roman numerals. These numerals are known as the Stock system of naming chemical ions and elements) -1 -2 -3 -4 MONATOMIC IONS Fluoride F-1 Oxide O-2 Nitride N-3 Chloride Cl-1 Sulfide S-2 Phosphide P-3 Bromide Br-1 Iodide I-1

There are also combinations of covalently bonded atoms that also have a charge called polyatomic ions N H 4 +1 C O 3 -2 P O 4 -3 H O -1 Poly- means many, but we treat each of these polyatomic ions as a single unit with a single charge

+1 +2 -1 -2 -3 POLYATOMIC IONS Ammonium NH4+ Dimercury Hg2+2 Acetate C2H3O2- Carbonate CO3-2 Phosphate PO4-3 Bromate BrO3- Chromate CrO4-2 Arsenate AsO4-3 Chlorate ClO3- Dichromate Cr2O7-2 Chlorite ClO2- Hydrogen Phosphate HPO4-2 Cyanide CN- Oxalate C2O4-2 Dihydrogen Phosphate H2PO4- Peroxide O2-2 Hydrogen Carbonate HCO3- Sulfate SO4-2 Hydrogen sulfate HSO4- Sulfite SO3-2 Hydroxide OH- Hypochlorite ClO- POLYATOMIC IONS

-1 -2 -3 POLYATOMIC IONS Nitrate NO3- Nitrite NO2- Perchlorate ClO4- Permanganate MnO4- POLYATOMIC IONS

Today is all about combining these electrically charged ions together to form stable compounds. Reminder: when two atoms combine transferring valence electrons it is called an ionic bond. Oppositely charged ions attract each other and form an ionic bond that is electrically neutral, to establish a molecule that is neutral.

Looking at the structure of salt shows that the attraction between ions is so great that many sodium ions and chloride ions become involved.

The results of each ion being surrounded by several other ions allows the attraction between oppositely charged ions to be much greater than the repulsion between ions with the same charge. The strong attraction between the ions, & the orderly arrangement in the crystal affect the properties of the compound.

Cations & anions are pulled together in a tightly packed structure, giving each crystal a characteristic shape The simplest repeating unit of anions and cations is called a unit cell.

Properties of ionic compounds Can conduct electricity When melted it frees up the ions to move past each other Pack in highly ordered arrangements Ions in a salt form repeating patterns called a crystal lattice

Properties of ionic compounds Hard Packed into layers, takes a lot of energy to break all of the bonds Brittle If a force is strong enough to reposition a layer then the repulsive forces drive ions apart

Properties of ionic compounds High melting points and boiling points Because of strong attraction between ions, it takes a lot of energy to break them apart

Predicting the formation of ionic compounds. We can predict the combinations of ions and the formation of their ionic formulas, knowing how ions interact We can have 2 different kinds of ionic compounds formed: binary or ternary

WRITING IONIC FORMULAS There are a couple of rules to follow to make sure that the proper ionic formula is written.

The sum of the ions’ charges must be zero RULE #1 Ions will combine only in the simplest whole number ratio which cancels out the charge to form a neutral compound The sum of the ions’ charges must be zero 3(+1) + (-3) = 0 +2 + (-2) = 0

It’s better to be positive than negative  RULE #2 The compound formula is ALWAYS written with the cation first then the anion. It’s better to be positive than negative  NaCl ClNa

Some ionic compounds’ charges automatically cancel each other out. K +1 + I -1 KI Mg +2 + O -2 MgO

How do we decide the proper ratio of cations and anions? What if we were forming ionic compounds with ions whose charges don’t add up to a charge of 0? How do we decide the proper ratio of cations and anions?

What if we had three chlorine ions for every one Aluminum ion? +3 + Cl -1 =2 What if we had three chlorine ions for every one Aluminum ion? Al +3 + 3 Cl -1 AlCl 3

We need to find the ratio Al +3 & O -2 We need to find the ratio of ions that will make the charges cancel out to a neutral compound. 2 Al +3 & 3 O -2 Al O 3 2

IT’S NOT A TRICK SO MUCH AS A SHORTCUT! We have a trick that will help us know the number of the ions to make a neutral compound. IT’S NOT A TRICK SO MUCH AS A SHORTCUT!

CRISS-CROSS RULE: Al +3 + Cl -1 AlCl 3 Ca +2 + P -3 Ca 3 2 P

Using polyatomic ions To write the formulas for compounds containing polyatomic ions, follow the rules for writing formulas for binary compounds, with one additional consideration. We add parentheses around the polyatomic ion when more than one of the ion is needed to develop the proper ratio.

Al +3 + OH -1 Al(OH) 3 Na +1 4 + SO -2 Na SO 4 2

Practice Writing Formulas Ca+2 & O-2  Sn+4 & CO3-2  NH4+1 & SO4-2  Mg+2 & C2H3O2-1  CaO Sn(CO3)2 (NH4)2SO4 Mg(C2H3O2)2

NAMING THEM Most of the time you can name an ionic compound by 1) Writing the name of the first element 2) Writing the root of the name of the second element 3) Adding -ide to the root

Names of negative ions Parent element Negative ion Chlorine Chloride Oxygen Oxide Nitrogen Nitride Phosphorus Phosphide Fluorine Fluoride Iodine Iodide Sulfur Sulfide Bromine Bromide

CaCl2  K3P  Al2S3  NAMING THEM Calcium chloride Potassium phosphide Aluminum sulfide

NAMING THEM Some of our metals have more than one ionic charge We have to determine the charge on the metal We then indicate the charge as a roman numeral

FeCl2  FeCl3  PbBr2  Iron(II) chloride Iron (III) chloride NAMING THEM FeCl2  FeCl3  PbBr2  Iron(II) chloride Iron (III) chloride Lead (II) bromide

NAMING THEM If the compound has a polyatomic ion in it 1) name the first element, including the roman numeral if appropriate 2) then name the polyatomic ion

Fe(OH)2  Ca3 (PO4)2  Na2SO4  NAMING THEM Iron(II) hydroxide Calcium phosphate Sodium sulfate

Strontium Nitrite  Sr(NO2)2 CuOH  Copper (I) hydroxide Lead (IV) phosphide  Pb3P4 NH4OH  Ammonium hydroxide Sodium carbonate  Na2CO3