Chemical Bonds Chapter 22

Stability in Bonding Section 1

Properties of Combined Elements When combining elements, new properties emerge Copper is a shiny, copper colored metal Sulfur is pale, yellow solid Oxygen is a colorless, odorless gas Copper Sulfate (Cu2SO4) is a blue crystalline salt that is used in pesticides

Formulas Formulas are like recipes A chemical formula will tell you What elements are included The exact number of atoms of each element are found in a unit of that compound Subscripts are used to show how many of each atom are present Changing the subscript changes the compound

Some Familiar Compounds Familiar Name Chemical Name Formula Sand Silicon dioxide SiO2 Milk of Magnesia Magnesium hydroxide Mg(OH)2 Cane Sugar Sucrose C12O22O11 Lime Calcium oxide CaO Vinegar Acetic acid CH3COOH Laughing Gas Dinitrogen oxide N2O Grain Alcohol Ethanol C2H5OH Battery Acid Sulfuric acid H2SO4 Stomach Acid Hydrochloric acid HCl

Atomic Stability Electrons in the outer energy level of an atom are considered the bonding electrons Bonding electrons are called valence electrons An atom is considered stable when it has 8 electrons in its outer shell An atom with 8 electrons in its outer energy level will NOT form bonds (except Period 1 elements) The noble gases will not form bonds are considered inert

The Quest to be Noble Atoms of elements that don’t naturally have 8 electrons in the outer energy level will lose, gain, or share electrons to become stable Sodium will give an electron away Chlorine will take an electron Atoms that that gain or lose electrons become ions Ions are charged particles because they have either fewer or greater electrons than protons

Ions Positively charged ions are called cations Ca+2, Na+1 Metals will form cations Negatively charged ions are called anions O-2, N-3 Non-metal will form anions

Ionic Bonds

Chemical Bonds When atoms give, take, or share electrons chemical bonds are formed A chemical bond is a force that holds atoms together in a compound. Remember: Compounds will have different physical and chemical properties that the atoms that make them up The two types of chemical bond that form compounds are Ionic Covalent

Ionic Bonding Atoms are in constant motion When two or more atoms collide they may form a bond In ionic bonding, the collision results in one atom taking an electron(s) from the other Ionic bonding results from the transfer of electrons Ionic bonds will always involve a metal atom transferring its electrons to a non-metal atom The transfer of electrons in ionic bonds result in the release of large amounts of energy

Ionic Bonds Let’s take potassium (K) Now consider Iodine (I) 1 electron in its outer energy level (4th level) Becomes stable by giving an electron away so that its 3rd level, the new outer level, will be full Now consider Iodine (I) 7 electrons in its outer shell Will need one more electron to fill its outer energy level In a collision, Iodine will take Potassium’s electron Potassium and Iodine are now ions They have opposite charges Charges are known as oxidation numbers The attract one another and form an ionic bond (KI)

Ionic Bonds and Net Charge The end result of an ionic bond is a net charge on the compound of 0 Potassium ended up with a charge of +1 Iodine ended up with a charge of -1 KI has a net charge of 0 because the charges cancel

Ionic Bonds Ionic bonds can involve more than one electron Let’s consider Magnesium (Mg) Metal Has two electrons in its outer shell Will give up both electrons to achieve stability Will form a +2 cation Now for Chlorine (Cl) Non-metal Has seven electrons in its outer shell Only needs on electron to achieve stability Will form a -1 anion Magnesium will give one electron to two different Chlorine atoms MgCl2 2 + (– 1) + (–1) = Net charge of 0

Writing Ionic Formulas Write the symbol of the element that has the positive oxidation number or charge first Write the symbol of the element with the negative oxidation number or charge second Balance the charges

Naming Ionic Compound Write the name of the cation Write the root name of the negative ion Add –ide to the root

Special Metal Ions Many of the transition metals can form more than one ion Ions for transition metals that have more than one ion are designated using Roman numerals The Roman numeral is equal to the charge on the ion Name Oxidation Number Copper (I) 1+ Copper (II) 2+ Iron (II) Iron (III) 3+ Chromium (II) Chromium (III) Lead (II) Lead (IV) 4+

Writing Formulas and Naming Compounds with Special Ions Copper (II) Oxide Cu 2+ O 2- CuO Chromium (III) chloride Cr 3+ Cl -1 CrCl3 CuCl2 What is the charge on the anion? -1 What is the total negative charge? -2 So what must the charge on the cation be? +2 So it must be Copper (II) Include the Roman numeral in the name Copper (II) chloride

Compounds with Polyatomic Ions Not all compounds are binary Some are polyatomic “poly” means many A polyatomic ion is a positively or negative charged, covalently bonded group of atoms They act as a single ion

Naming & Writing Compounds with Polyatomic Ions To name a compound that contains a polyatomic, just use the name of the polyatomic ion whenever it appears Do not add –ide if using a polyatomic anion If more than one polyatomic atom is used, put parenthesis around the atom before using the subscript Charge Name Formula 1+ ammonium NH4+ 1- Acetate Chlorate Hydroxide Nitrate C2H3O2- ClO3- OH- NO3- 2- Carbonate sulfate CO32- SO42- 3- Phosphate PO43-

Naming & Writing Compounds with Polyatomic Ions Ammonium phosphate Ammonium NH4+ Phosphate PO4 3- You need three ammonium ions for every one phosphate ion (NH4)3PO4 Calcium Chlorate Calcium Ca+2 Chlorate ClO3- You need two chlorate ions for every calcium ion Ca(ClO3)2

Compounds with Added Water Some ionic compounds have water molecules as part of their structure They are called hydrates The water can be removed if heated The resulting crystals are anhydrous Anhydrous means “without water” Hydrates have water chemically attached to its ions and written into its chemical formula

Naming Hydrates CoCl2 • 6H20 CaSO4 • 2H20 Cobalt chloride hexahydrate Calcium sulfate dihydrate Name Number of Atoms Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8 Name Number of Atoms Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8

Covalent Bonding

Covalent Bonding Form between two non-metals When two non-metals bond, neither is very willing to give up its electrons They end up sharing electrons A compound that results form a covalent bond is called a molecule

Single Covalent Bonds Involves sharing two electrons Water has two single bonds Each hydrogen atom contributes one electron Oxygen provides one for sharing to each hydrogen atom

Multiple Bonds A covalent bond can also contain more than one pair of shared electrons Double Bonds Involve 4 electrons O2 Each oxygen needs two electrons Triple Bonds Involve 6 electrons N2 Each nitrogen needs three electrons

Polar Bond Electrons are not always shared equally The strength of the attraction of each atom to its outer electrons is related to its size The further the electron is away from the nucleus, the weaker the attraction The larger the nucleus the greater the attraction The electrons will spend more time near the stronger atom A partial negative sign is assigned to the stronger atom A partial negative sign is assigned to the weaker atoms

Polar vs Nonpolar Molecules that don’t share their electrons equally are called polar molecules Water Molecules that share their electrons equally are non-polar Non-polar molecules are more symmetrical or involve bonding of two identical molecules CCl4 O2

Naming Binary Covalent Compounds The prefixed used in naming hydrates are used when naming binary covalent compounds Mono- is often omitted from the formula name The last vowel of the prefix is dropped if the second element begins with a vowel The second element still ends in -ide N2O Dinitrogen dioxide N2O5 Dinitrogen pentoxide

Properties of Compounds Covalent Compounds Bonds are strong but attraction between molecules is weak Melting points and boiling points are lower Will be solid, liquid, or gas Solid form will be soft Poor electrical and thermal conductors Ionic Compounds Bonds are strong Higher melting points Higher boiling points Hard and brittle solids Dissolved in a liquid, they will conduct electricity