Ch 8 - Compounds & Molecules

Ch 8 - Compounds & Molecules
8.1 Ionic Compounds – Fr 2-28 8.2 Molecular Compounds - Fr 29-52 8.3 Intermolecular Forces – Fr 8.4 Formula Masses – Fr

In early chapters we discussed physical and chemical properties
In later chapters we discussed atom structures and chemical bonding

How are they related? Atom structures and chemical bonding
Physical and chemical properties How are they related?

Structure of NaCl We have seen that in an ionic salt
each atom interacts with all its neighbors. Each chloride ion is attracted to all nearby sodium ions Each sodium ion is attracted to all nearby chloride ions

In any ionic crystal, the ratio of positive ions to negative ions must allow for all of the positive charge to cancel out all of the negative charge. Lead(II) sulfide (PbS) Aluminum oxide (Al2O3) Copper(II) sulfate (CuSO4) Pb2+ and S2– (+2) and (–2) 2Al3+ and 3O2– (+6) and (–6) Cu2+ and SO42– (+2) and (–2)

Properties The ionic structure leads to the following physical properties: Ionic substances are solid at room temperature Ionic substances have very high melting points To be in a liquid state, there must be enough energy for each atom to break free from the attractive forces from its neighbors.

The interconnected network of bonds holds the entire crystal together
Properties The ionic structure leads to the following physical properties: Ionic substances are solid at room temperature Ionic substances have very high melting points Ionic substances are hard The interconnected network of bonds holds the entire crystal together

Properties The ionic structure leads to the following physical properties: Ionic substances are solid at room temperature Ionic substances have very high melting points Ionic substances are hard but brittle Ionic substances are brittle, which means they break

Properties When melted or dissolved, ions are free to move around, making it possible for an ionic solution to conduct electricity Ions dissolved in water move in random directions by colliding with water molecules Overall ion movement toward the electrodes creates an electrical current

Polyatomic ions An ion does not have to be a single atom. An ion can be a small molecule with a charge. a monatomic ion a polyatomic ion

The CO3 molecule needs two extra electrons.
Polyatomic ions Calcium carbonate, CaCO3 The calcium ion contributes a +2 charge (Ca2+) The CO3 molecule needs two extra electrons.

Polyatomic ions The two oxygens now have a –1 charge,
giving the whole molecule a –2 charge The carbonate ion switches among these three versions.

Ammonium sulfate (NH4)2SO4 is made from two polyatomic ions

Now we will learn how to:
Write formulas for ionic compounds Write names for ionic compounds Name ions with transition metals

Writing formulas Balancing positive and negative charge in ionic formula writing

Writing formulas Write the correct formulas for the compounds that will form using the following ion pairs: Mg2+ and Cl–, Na+ and S2–, Al3+ and O2–.

Writing names With monatomic ions:

Writing names Names for polyatomic ions

Writing names With monatomic ions: With polyatomic ions:

Most transition metals can have different charges
Naming transition metal ions Most transition metals can have different charges A Roman numeral indicates the charge on a positive ion Check whether a Roman numeral is necessary for elements in the highlighted parts of the periodic table

Naming transition metal ions
Consider PbCl2 Check the common ions table Use the negative ion to determine the charge on lead With only one Pb ion, and a total charge of +2 needed, the Pb ion must be lead(II)

Naming transition metal ions
Consider ZnSO4 Check the common ions table Zn only forms a +2 ion No Roman numeral is needed

Write the names for each of the following formulas: CaCl2, Zn(NO3)2, Fe3(PO4)2.
Asked: Names for the formulas above Given: Three formulas and a common ion table Relationships: The name of each formula is constructed form the name of the ions. If the negative ion is a single atom, modify the name of the element to end in “-ide.” If the positive ion might form multiple charges, make sure to use a Roman numeral in the name.

Asked: Names for the formulas above
Write the names for each of the following formulas: CaCl2, Zn(NO3)2, Fe3(PO4)2. Asked: Names for the formulas above Given: Three formulas and a common ion table Relationships: The name of each formula is constructed form the name of the ions. If the negative ion is a single atom, modify the name of the element to end in “-ide.” If the positive ion might form multiple charges, make sure to use a Roman numeral in the name. Solve: CaCl2 is calcium chloride. Zn(NO3)2 is zinc nitrate. Fe3(PO4)2 is iron(II) phosphate.

with three sulfur atoms
Naming simple molecular compounds Consider the following molecular compound: P2S3 two phosphorous atoms with three sulfur atoms diphosphorous trisulfide

(another name for water)
Naming simple molecular compounds Consider the following molecular compound: H2O two hydrogen atoms with one oxygen atom dihydrogen monoxide (another name for water)

CO Naming simple molecular compounds
Consider the following molecular compound: CO one carbon atom with one oxygen atom Drop “mono” for the first element carbon monoxide

Write the name for each of the following formulas:
Naming simple molecular compounds Write the name for each of the following formulas: N2O4, S2F10, SO3.

Naming simple molecular compounds
Write the name for each of the following formulas: N2O4, S2F10, and SO3. Solve: N2O4 is dinitrogen tetraoxide. S2F10 is disulfur decafluoride. SO3 is sulfur trioxide.

Some are hard and brittle; some are flexible, soft or mushy
Properties of molecular compounds vary widely Hardness Some are hard and brittle; some are flexible, soft or mushy State of matter They can be solid, liquid or gas at room temperature Boiling points Their boiling points can vary from –253oC to over 1,000oC Ability to conduct electricity Most do not conduct electricity well

Water Water is a covalent compound
About eight million billion billion (1024) water molecules make up this cup of water Water is a covalent compound Properties of molecular substances depend on: - the structure of the individual molecule - the attractions between molecules

Molecules can be classified into different categories
Small Medium Wax, one of the main hydrocarbons in beeswax Caffeine, found in tea, coffee, and soda

Molecules can be classified into different categories
Large: polymer Large: network Protein, molecule on the right shows a thick line tracing the linear chain with red and blue marking either end Graphene, layers of which make graphite

is a liquid at room temperature
Small molecules Most small molecules (no more than a dozen atoms) are liquids or gases at room temperature Some of the most important molecules related to our ecosystem are small molecules Acetaminophen (Tylenol) is a liquid at room temperature

(no more than a dozen atoms) are liquids or gases at room temperature
Most small molecules (no more than a dozen atoms) are liquids or gases at room temperature If ice did not float, ponds would freeze from the bottom up, killing everything inside. Some of the most important molecules related to our ecosystem are small molecules Water

Small molecules Ethene (or ethylene) Ethanol
Nonpolar (gas at room temperature) Boiling point = –103.7oC Ethylene is a gas that causes fruits to ripen. Polar (liquid at room temperature) Boiling point = 78.4oC

Candle wax is a mixture of medium-sized hydrocarbons
Medium-sized molecules Medium-sized molecules (no more than 100 atoms) tend to be liquids or soft solids at room temperature. They are often long-chain hydrocarbons or lipids Candle wax is a mixture of medium-sized hydrocarbons hydrocarbon: a molecule made entirely from carbon and hydrogen atoms.

Linoleic acid, a major component of vegetable oil
Medium-sized molecules Lipids are typically fats or steroids Fats are nonpolar and insoluble in water Linoleic acid, a major component of vegetable oil

Medium-sized molecules
Most steroids have four rings of carbon atoms. They can act as hormones, drugs, vitamins, or poisons 3 1 4 2 Testosterone (a steroid)

A single monomer of vinyl chloride
Polymers Polyvinyl chloride (PVC) is made by bonding many vinyl chloride monomers together A single monomer of vinyl chloride A single polymer chain typically contains hundreds to thousands of atoms

Polymers Recycling symbols and polymer codes
Polyvinyl chloride polymer: a long chain molecule formed by connecting small repeating units with covalent bonds. monomer: a small molecule that is a building block of larger molecules called polymers.

Polymers Homopolymers are made from only one type of monomer
Starch fragment Homopolymers are made from only one type of monomer Glucose a natural monomer Cellulose fragment

Networks Silicon dioxide (or quartz) is a mineral in sand Since every atom in quartz is covalently bonded together, the entire grain can be considered a single network. network covalent: a type of large structure, usually made from hundreds to billions of atoms, in which each atom is covalently bonded to multiple neighboring atoms, forming a web of connections.

Carbon forms many types of network covalent substances
Networks Carbon forms many types of network covalent substances Diamond Buckyballs Carbon nanotubes Graphite

Chemical formulas Use the empirical formula to describe the simplest ratio of elements of that substance a molecule of water Use the molecular formula to indicate the exact type and number of each atom in a single molecule of that substance A sample of ionic or network covalent substance is a single bonded unit of material

Chemical formulas Empirical formula: Molecular formula: CH C6H6
a molecule of water Benzene Use the molecular formula to indicate the exact type and number of each atom in a single molecule of that substance Empirical formula: Molecular formula: CH C6H6

Chemical formulas Write the molecular formula for each of the following molecules:

Chemical formulas Write the molecular formula for each of the following molecules: Asked: The molecular formula Relationships: The formula should reflect the exact number and type of atoms in an individual molecule of the substance. Solve: A. C2H B. NH C. C2H5O

We have seen in Chapter 3 that molecules in solids and liquids are held together by intermolecular forces In this section, we are going to discuss the different types of intermolecular forces that exist, why they are present and how strong they are. Not all liquid molecules, for instance, will experience the same intermolecular forces. What are these forces? Where do they come from? Do all molecules feel them?

A quick look at water Intermolecular attraction A tiny drop of water As a liquid, water molecules can move around but intermolecular forces keep them from separating completely to become a gas.

Types of intermolecular attractions
Between polar molecules Between nonpolar molecules London dispersion Dipole-dipole Hydrogen bonding Intermolecular attractions weak strong Intermolecular attractions are also called van der Waals attractions

Dipole-dipole attractions
Like water, formaldehyde is a polar molecule The polar covalent C=O bond makes the entire molecule polar We say the molecule has a dipole dipole-dipole attraction: the attractions between the positive part of one polar molecule and the negative part of another polar molecule.

Like water, formaldehyde is a polar molecule Dipole-dipole attractions Dipole-dipole attractions cause formaldehyde to condense into a liquid at room temperature

more Molecules that are more polar will attract strongly. less Dipole-dipole attractions

more Molecules that are more polar will attract strongly. less Boiling point Molecules that attract more strongly will have a boiling point. higher lower

Higher polarity molecules attract more strongly and have a higher boiling point propane 1-propanol 1,3-propanediol Boiling points –42oC 97oC 214oC least polar most polar

Hydrogen bonding Electronegativity There is a moderate difference in electronegativity between H and F, O and N (0.94 to 1.88)

Hydrogen bonding Water molecules are held together by a network of hydrogen bonding

Hydrogen bonding One special property of water:
Ice is less dense than water in the liquid form There is more space in between water molecules in ice Water in the liquid form Iceberg photo courtesy of NOAA

Hydrogen bonding Why a drop of water doesn’t “lie flat” on a hard surface: H-bonds keep the water molecules together In reality water molecules are much, much smaller than on the drawing! surface tension: a force acting to pull a liquid surface into the smallest possible area.

Hydrogen bonding Surface tension from hydrogen bonds allows a water strider to “walk” on water

Hydrogen bonding Hydrogen bonding plays a crucial role in DNA and protein structures Hydrogen bonds DNA uses hydrogen bonds to hold the two strands together

Hydrogen bonding Hydrogen bonding plays a crucial role in DNA and protein structures The protein structure is stabilized with H bonds

Hydrogen bonding Paper glue is a mixture of polyvinyl acetate (PVA) and water In “wet” glue, polymer molecules are lubricated by water

Hydrogen bonding Paper glue is a mixture of polyvinyl acetate (PVA) and water In “wet” glue, polymer molecules are lubricated by water As glue dries, many more H-bonds form between the polymer molecules, so the glue hardens

London dispersion Isolated hydrogen molecules are nonpolar
A temporary, very small polarity can be induced when nonpolar molecules are close enough

London dispersion Molecules with a larger surface area
will attract ____strongly. more less propane A temporary, very small polarity can be induced when nonpolar molecules are close enough Polarizability is greater in a molecule with an elongated shape than in a molecule that is globular. pentane

will attract ____strongly. more less propane A temporary, very small polarity can be induced when nonpolar molecules are close enough pentane

will attract ____strongly. more less Boiling point Molecules that attract more strongly will have a boiling point. higher If molecules attract strongly, they are less likely to be in the gas phase. More energy will be required to overcome these attractive intermolecular forces. Therefore, the boiling point will be higher. lower

will attract ____strongly. more less Boiling point Molecules that attract more strongly will have a boiling point. higher lower (It takes more energy to overcome the intermolecular forces.)

London dispersion Molecules with larger surface area attract more strongly and have a higher boiling point propane butane pentane Boiling points –42oC 0oC 36oC least surface area most surface area

London dispersion The shape of the molecule also matters!
About the same surface area Stronger attraction Weaker attraction Higher boiling point Lower boiling point

Atomic mass is the molar mass for that element

Molar mass H2SO4 Calculating molar mass
Subscripts apply only to the element or group they follow H2SO4 For H: 2 x g/mole = g/mole For S: 1 x g/mole = g/mole For O: 4 x g/mole = g/mole For H2SO4: g/mole

Molar mass (NH4)3PO4 Calculating molar mass
If the subscript follows a parenthesis, then multiply everything inside the parentheses by the subscript (NH4)3PO4 For N: x g/mole = g/mole For H: 12 x g/mole = g/mole For P: 1 x g/mole = g/mole For O: x g/mole = g/mole For (NH4)3PO4: g/mole

Molar mass What is the molar mass of aluminum carbonate, Al2(CO3)3?

Molar mass What is the molar mass of aluminum carbonate, Al2(CO3)3?
Asked: The molar mass Given: The name of the formula Relationships: The name of the formula can be used to determine the ratios of elements in the formula. Then the periodic table can be used to get the molar mass of each of the elements used. Solve: Aluminum carbonate is ionic, so the formula is Al2(CO3)3.

NaCl Percent composition
You can identify a compound using the percent mass of each element. % by atom number Na: 50% Cl: 50% NaCl 1 mole of Cl is heavier than 1 mole of Na % by mass Na: 39% Cl: 61%

Two types of problems Calculate % composition using a chemical formula
Find the % composition of Ca3(PO4)2. Calculate % composition with a measured sample We know the % composition of a white powder. Determine if this powder is common table sugar.

Percent composition Find the % composition of Ca3(PO4)2.
1. Calculate the molar mass 2. Calculate the percent of each element in a mole of the substance For Ca: x = g/mole For P: 2 x = g/mole For O: x = g/mole For Ca3PO4: g/mole

Percent composition Find the % composition of Ca3(PO4)2.
1. Calculate the molar mass 2. Calculate the percent of each element in a mole of the substance Ca: g/mole P: g/mole O: g/mole Ca3PO4: g/mole

Two types of problems Calculate % composition using a chemical formula
Find the % composition of Ca3PO4. Calculate % composition with a measured sample We know the % composition of a white powder. Determine if this powder is common table sugar.

Percent composition A white powder can be broken down into 1.05 g of C, 0.16 g of H2, and 1.29 g of O2. Is this powder common table sugar, also known as sucrose (C12H22O11)? 1. Add up the individual mass measurements to get the total mass 2. Calculate the percent composition of the unknown 3. Compare with the percent composition of sucrose 1.05 g 0.16 g 1.29 g 2.50 g C: H2: O2: Total of unknown:

Percent composition A white powder can be broken down into 1.05 g of C, 0.16 g of H2, and 1.29 g of O2. Is this powder common table sugar, also known as sucrose (C12H22O11)? 1. Add up the individual mass measurements to get the total mass 2. Calculate the percent composition of the unknown 3. Compare with the percent composition of sucrose Total of unknown: 2.50 g

Percent composition A white powder can be broken down into 1.05 g of C, 0.16 g of H2, and 1.29 g of O2. Is this powder common table sugar, also known as sucrose (C12H22O11)? 1. Add up the individual mass measurements to get the total mass 2. Calculate the percent composition of the unknown 3. Compare with the percent composition of sucrose For sucrose:

Percent composition A white powder can be broken down into 1.05 g of C, 0.16 g of H2, and 1.29 g of O2. Is this powder common table sugar, also known as sucrose (C12H22O11)? YES! The percent composition is very close, so the unknown is probably sugar % composition of sucrose: % composition of unknown: % C: % % H: % % O: %

Empirical formulas Na6Cl6 NaCl
The empirical formula is the one with the simplest ratio Na Na Cl Cl Cl Na Na6Cl6 NaCl Na Cl Na Na Cl 6:6 ratio 1:1 ratio Cl Cl Na

smallest number of moles
Empirical formulas Calculating an empirical formula 1. Convert grams to moles 2. Simplify the mole ratio 3. Write the formula Assume you have a sample that is g hydrogen and 4.00 g oxygen. H2O smallest number of moles

Empirical formulas Cu2O
A jar of powder is labeled copper oxide, but you do not know whether the copper is Cu+ or Cu2+. After taking a small sample you find that it is made from 2.96 g of copper and 0.37 g of oxygen. What is the correct name and formula for the ionic compound in that jar? 1. Convert grams to moles 2. Simplify the mole ratio 3. Write the formula Cu2O

Empirical formulas Cu2O Copper(I) oxide Cu2+ O2– Cu+ O2–
A jar of powder is labeled copper oxide, but you do not know whether the copper is Cu+ or Cu2+. After taking a small sample you find that it is made from 2.96 g of copper and 0.37 g of oxygen. What is the correct name and formula for the ionic compound in that jar? Copper(I) oxide Cu2+ O2– Cu+ O2– Cu2O +4 –2 +2 –2

smallest number of moles
Empirical formulas Calculating an empirical formula 1. Convert grams to moles 2. Simplify the mole ratio 3. Write the formula Assume you have a sample that is g hydrogen and 4.00 g oxygen. H2O smallest number of moles

Empirical formulas Cu2O
A jar of powder is labeled copper oxide, but you do not know whether the copper is Cu+ or Cu2+. After taking a small sample you find that it is made from 2.96 g of copper and 0.37 g of oxygen. What is the correct name and formula for the ionic compound in that jar? 1. Convert grams to moles 2. Simplify the mole ratio 3. Write the formula Cu2O

Empirical formulas Cu2O Copper(I) oxide Cu2+ O2– Cu+ O2–
A jar of powder is labeled copper oxide, but you do not know whether the copper is Cu+ or Cu2+. After taking a small sample you find that it is made from 2.96 g of copper and 0.37 g of oxygen. What is the correct name and formula for the ionic compound in that jar? Copper(I) oxide Cu2+ O2– Cu+ O2– Cu2O +4 –2 +2 –2

Molecular formulas The empirical formula can be the same as the molecular formula… Empirical formula Molecular formula CH2O CH2O Formaldehyde …but not always. Glucose CH2O C6H12O6

Molecular formulas CH2O C6H12O6
The molecular mass will always be equal to, or a multiple of, the empirical formula mass. Empirical formula Molecular formula x 6 CH2O C6H12O6 Glucose x 6 30.03 g/mole g/mole

Molecular formulas CH C?H? 13.018 g/mole 78.11 g/mole
Given the following empirical formula and molar mass, determine the molecular formula for CH (78.11 g/mole). Empirical formula Molecular formula CH C?H? g/mole 78.11 g/mole For CH: = g/mole

Molecular formulas CH C6H6 13.018 g/mole 78.11 g/mole
Given the following empirical formula and molar mass, determine the molecular formula for CH (78.11 g/mole). Empirical formula Molecular formula CH C6H6 x 6 g/mole 78.11 g/mole The molecular formula is C6H6

Two types of problems: Calculate % composition using a chemical formula Find the % composition of Ca3(PO4)2. Calculate % composition with a measured sample We know the % composition of a white powder. Determine if this powder is common table sugar.

The empirical formula can be the same as the molecular formula…
CH2O CH2O Formaldehyde …but not always. x 6 CH2O C6H12O6 Glucose x 6 30 g/mole 180 g/mole

Ch 8 - Compounds & Molecules

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