Naming Compounds and Writing Formulas GPS 9

Octet Rule: Forming Bonds Atoms will gain, lose, or share electrons in order to fulfill the octet rule (to obtain a full outer energy level) When electrons are shared, covalent bonds are formed When electrons are transferred, ions are formed. Ions are attracted to each other and form ionic bonds

Ionic Bonding – often occurs between metal ions and nonmetal ions – involves a transfer of valence electrons – ions are separate, but are attracted to one another because of opposite charges (one + ion, one - ion) – ions form a compound called a solid crystal lattice Example: Na and Cl react to form sodium chloride (NaCl) Solid NaCl crystal lattice

Ionic Bonding: Electronegativity Difference Ionic bonds form due to a transfer of electrons. Electrons are transferred from one atom to another because of a relatively large difference in electronegativity between a metal and nonmetal.

Oxidation number of Groups Oxidation Numbers

Naming Ions Recall: oxidation numbers tell us which ion is formed during chemical reactions Naming ions – (name of metal) ion – (name of nonmetal) –ide ion Examples – Na 1+ sodium ion – O 2- oxide ion

Naming Ions Name the following ions: Mg 2+ F 1- Cl 1- magnesium ion fluoride ion chloride ion

Writing Formulas for Ionic Compounds magnesium oxideMgO potassium chlorideKCl

Writing Formulas for Ionic Compounds sodium oxideNa 2 O beryllium bromideBeBr 2

Writing Formulas for Ionic Compounds aluminum sulfideAl 2 S 3

Writing Formulas for Ionic Compounds Atoms ionically bond in ratios that allow them to fulfill the octet rule, forming neutral compounds. Mathematically, it works to “criss-cross” so that the charge on each ion becomes the subscript for the other ion it is bonded to. Examples:

Writing Formulas for Ionic Compounds Write the chemical formula for the compound that forms when the following elements bond: 1. magnesiumchlorine 2. lithiumnitrogen MgCl 2 Li 3 N

Writing Formulas for Ionic Compounds Make sure you simplify your formula so that it has the smallest subscripts possible. Examples: Calcium reacts with Sulfur: Ca 2+ S 2- Ca 2 S 2 Simplify to CaS

Writing Formulas for Ionic Compounds Write the chemical formula for the compound that forms when the following elements bond: 1. boronnitrogen 2. magnesiumsilicon BN Mg 2 Si

Formulas for Ionic Compounds with a Transition Metal Many transition metals, lead (Pb), and tin (Sn) have multiple possible oxidation numbers Example: Copper commonly forms ions with a +1 or +2 charge. Roman numerals are used to distinguish between oxidation states: Copper (I)Copper (II)

Roman Numerals Indicate Oxidation Number Roman NumeralOxidation number I+1 II+2 III+3 IV+4 V+5 VI+6 VII+7 VIII+8 IX+9 X+10

Formulas for Ionic Compounds with a Transition Metal Write the chemical formula for the compound that forms when the following elements bond: 1. iron(III)oxygen 2. chromium(VI)sulfur Fe 2 O 3 CrS 3

Formulas for Ionic Compounds with a Transition Metal Some transition metals always have the same oxidation number, therefore no roman numeral is used when named Determine the formula for each of the following: – Silver chloride – Zinc chloride Transition metalOxidation numberIon symbol Silver1+1+ Ag + Zinc2+2+ Zn 2+ Cadmium2+2+ Cd 2+

Naming Ionic Compounds ** We use the IUPAC naming system** (International Union of Pure and Applied Chemistry) Steps 1. Write the name of the metal 2. If the metal is a transition metal or Pb or Sn, use a roman numeral to indicate the charge (oxidation number) 3. Write the name of the nonmetal, changing the ending to –ide Examples: NaClsodium chloride MgBr 2 magnesium bromide Fe 2 O 3 iron (III) oxide PbI 4 lead (IV) iodide

Naming Ionic Compounds Using the IUPAC naming system, name the following compounds: MgCl 2 NiBr Li 2 O SnS 2

Naming Molecules (Covalently-bound compounds) What about molecules? Name the following: CO 2 CO Why must there be a different way to name molecules compared to how we name ionic compounds?

Covalent Bonding – Usually occurs between two nonmetal atoms – involves a sharing of electrons – combine to form a molecule

Covalent Bonding: Electronegativity Difference Covalent bonds form due to a sharing of electrons. Electrons are shared between atoms because of a relatively small difference in electronegativity between nonmetals.

Law of Multiple Proportions Some atoms (typically nonmetals) share electrons because they have similar electronegativity. These atoms can combine in different ratios simply by sharing a different amount of electrons in order to fulfill the octet rule.

Naming Molecules: Multiple Proportions Law of multiple proportions - the proportion (ratio) in which elements combine canbe expressed in small whole numbers - nonmetals can combine in different ratios, therefore we must use prefixes when naming covalent molecules NO nitrogen monoxide NO 2 nitrogen dioxide

Naming Molecules: Prefixes The prefix indicates how many atoms of an element are present in a molecule. The prefix indicates the subscript in the formula for that element in the molecule. mono-1 di-2 tri-3 tetra-4 penta-5 hexa-6 hepta-7 octa-8 nona-9 deca-10

Naming Molecules ** We use the IUPAC naming system** (International Union of Pure and Applied Chemistry) Steps: 1.Use prefixes to indicate the subscript for each element. 2.Do not start the name of the molecules with “mono-” 3.Change the ending of the last element listed to “-ide” 4.Note: some metals and metalloids (like Be, B, and Ga) share electrons to create molecules due to their relatively low electronegativity Examples: N 2 O 5 PCl 5 BF 3 phosphorus pentachloride boron trifluoride dinitrogen pentoxide

Naming Molecules Using the IUPAC naming system, name the following compounds: N 3 O 7 NO P 2 O BeCl 2 trinitrogen heptoxide nitrogen monoxide diphosphorus monoxide beryllium dichloride

Common Substances’ Names: When naming these molecules use their common names, not the IUPAC naming system. H 2 Owater CH 4 methane NH 3 ammonia

Naming Summary Ionic CompoundMolecule What’s bonding? Metal and nonmetalUsually two nonmetals Naming Name of metal, then the nonmetal (changing ending to –ide) Use a roman numeral for the charge on transition metals, lead, or tin Name of the first nonmetal, then the second nonmetal (changing ending to – ide) Use prefixes to indicate subscripts Valence electrons Transferred between atoms to form cation(s) and anion(s) Shared between atoms Particle-view crystal lattice molecules

Mixed Practice: Formulas from Names Provide the formula for each of the following: Copper(II)oxide Sodium chloride phosphorus trichloride Magnesium phosphide Silver bromide dinitrogen pentoxide titanium(IV) sulfide

Mixed Practice: Names from Formulas Provide the name for each of the following: K 2 O P 2 O 4 MnO 2 CaBr 2 CCl 4 FeCl 3

Polyatomic Ions Polyatomic ions - many atoms bonded together with a single charge on the entire molecule ammonium ion, NH 4 + hydroxide ion, OH - acetate ion, C 2 H 3 O 2 -

Common Polyatomic Ions (Pre AP) IonName NH 4 + ammonium NO 2 - nitrite NO 3 - nitrate SO 3 2- sulfite SO 4 2- sulfate HSO 4 - hydrogen sulfate (bisulfate) OH - hydroxide PO 4 3- phosphate IonName NCS - thiocyanate CO 3 2- carbonate HCO 3 - Hydrogen carbonate (bicarbonate) ClO 3 - chlorate C2H3O2-C2H3O2- acetate MnO 4 - permanganate CrO 4 2- chromate O 2 2- peroxide

Polyatomic Ions Within a polyatomic ion, covalent bonds exist between nonmetals When bonding with another ion, polyatomic ions form ionic bonds ammonium chloride ammonium ion

Resonance structures - represent a pair of electrons being equally shared around the central atom - all bonds around the central atom are the same length due to the equal sharing of the pair of electrons resonance structures for carbonate ion, CO 3 2- resonance structures for nitrate ion, NO 3 -

Compounds Containing Polyatomic Ions: Writing Formulas Before using the “criss-cross” method, place parentheses around the polyatomic ion Example calcium nitrate Ca 2+ NO 3 - Ca(NO 3 ) 2

Compounds Containing Polyatomic Ions: Writing Formulas Write formulas for the following compounds: beryllium hydroxide sodium acetate iron(II) phosphate barium sulfate ammonium oxygen zinc nitrate

Naming Compounds Containing Polyatomic Ions Write the name for the following compounds: Cu(OH) 2 (NH 4 ) 2 O Li 3 PO 4 copper(II) hydroxide ammonium oxide lithium phosphate

Intro to Naming Acids Hydrogen bonded with an element: hydro__________ic acid Examples HBr H 2 S hydrobromic acid hydrosulfuric acid

Intro to Naming Acids Hydrogen bonded with a polyatomic ion: ______________ic acid Examples HNO 3 H 2 SO 4 nitric acid sulfuric acid

Types of Formulas Molecular formula – shows the true number of atoms of each element in a compound Empirical formula – shows the lowest (smallest) ratio of atoms in a compound Structural formula – shows the physical arrangement of atoms within a compound

Types of Formulas Example:Benzene Molecular formula – C 6 H 6 Empirical formula – CH Structural Formula

Types of Formulas Example: What type of formula is this? Give the molecular formula and the empirical formula for this molecule.

Types of Formulas If the molecular formula cannot be reduced, then the empirical formula is the same as the molecular formula. Example: If the molecular formula is C 3 H 7, what is the empirical formula?

Diatomic Molecules Naturally occurring diatomic molecules: Br 2, I 2, N 2, Cl 2, H 2, O 2, F 2 - These occur as gases at room temperature * except Br 2 (liquid at room temp) * except I 2 (solid at room temp) - Naming: Ex: O 2 oxygen gas N 2 nitrogen gas Br 2 liquid bromine I 2 solid iodine