ch. 6 the structure of matter. ch. 6 section 1 notes compounds and molecules –pg. 177-182

CH. 6 The Structure of Matter

Ch. 6 Section 1 Notes

• Compounds and Molecules– Pg. 177-182

Chemical Bonds

• The forces that hold atoms or ions together in a compound are called chemical bonds.– Can be broken, and the atoms rearrange

Chemical Structure

• The structure of a building is the way the building’s parts fit together– A compound’s chemical structure is the way

the atoms are bonded to make the compound

• Some models represent bond lengths and angles.– Bond length is the distance between the

nuclei of two bonded atoms– If a compound has 3 or more atoms, a bond

angle (the angle formed by two bonds to the same atom) tells which way there atoms point.

– Atoms are often represented by a ball-and-stick model to help you understand the compounds structure.

– Structural formulas also show the structures of compounds.• Chemical symbols are used to represent the atoms

– Space-filling model is another way to represent a water molecule.

• Shows the space that the oxygen and hydrogen atoms take up, or fill

• The chemical structure of a compound determines that properties of that compound.– Compounds with network structures are

strong solids.• Ex: quartz

– The strong bonds make the melting and boiling point of quartz and other minerals very high

• Some networks are made of bonded ions.– Ex: Table Salt (NaCl)

• Found in the form of regularly shaped crystals• Made of a repeating network connected by strong

bonds• Oppositely attracted ions• High melting and boiling point

• Some compounds are made of molecules.– Ex: sugar

• Molecules attract each other and form crystals

Nitrogen, Oxygen, and Carbon Dioxide

--Gases that are made of molecules

--Atoms are strongly attracted to each other and are bonded

• The strength of attractions between molecules varies.

• Sugar, water and Dihydrogen sulfide are all compounds made of molecules but have different properties

*The higher the melting point, the stronger the attraction between the atoms

• Hydrogen Bond– Oxygen atom of a water molecule is attracted

to a hydrogen atom of another molecule• Strong bonds within each water molecule• Weaker attractions between water molecules

Ch. 6 Section 2 Notes

• Ionic and Covalent Bonding– Pg. 183-190

Why do Chemical Bonds Form?• Atoms join to form bonds so that each

atom has a stable electron configuration.– One similar to a noble gas

• There are two kinds of chemical bonding:– Ionic Bonding – Covalent Bonding

Ionic Compounds

Covalent Compounds

StructureNetwork of bonded

ionsMolecules

Valence Electrons

Transferred Shared

Electrical conductivity

Good (when melted or dissolved)

Poor

State at room temp.

SolidSolid, liquid, or

gas

Melting and boiling points

Generally high Generally low

Ionic Bonds• Form from the attractions between such oppositely

charged ions.• Formed by the transfer of electrons

– Oppositely charged ions bond (NaCl)

• Ionic compounds are in the form of networks, not molecules.

• The formula unit of one sodium ion and one chloride ion is NaCl– NaCl ratio is 1:1

– CaF2 is 1:2

• When melted or dissolved in water,

ionic compounds conduct electricity. – Ions are free to move

when not is solid form.

Covalent Bonds• Compounds that are made of molecules,

such as water and sugar have covalent bonds.

• Atoms joined by covalent bonds share electrons.

• Usually form between nonmetal atoms.

• Can be solid, liquid or gas

• Low melting points

• MOST do not conduct electricity (not charged)

• Example: Cl2

– Each has 7 valence electrons.• Share one electron to have 8 valence electrons

and become stable.

Atoms may share more than one pair of electrons.

• When drawing the electron dot diagram, a line — means that there are 2 electrons being shared.

• If there is two lines ==, that is a double covalent bond (4 electrons being shared)

• A triple covalent bond is

formed by bonding two

nitrogen atoms

(total of 6 electrons)

Atoms do not always share electrons equally.

• When electrons are shared equally, they are called nonpolar covalent bonds. – Ex: Cl2

• When two atoms of different elements share electrons, the electrons are not shared equally and forms a polar covalent bond.– Ex: NH3

Metallic Bonds• Metals are flexible and conduct electric

current well because their atoms and electrons can move freely throughout a metal’s packed structure.

• Atoms in metals such as copper form metallic bonds.

Polyatomic Ions• Acts as a single unit in a

compound, just as ions that consist of a single atom do.

• Groups of covalently bonded atoms that have a positive or negative charge as a group.– Both covalent and ionic bonds

• There are many common polyatomic ions.

Parentheses group the atoms of a polyatomic ion.

• A polyatomic ions charge applies not only to the last atom in the formula but to the whole ion.

• A polyatomic ion acts as a single unit in a compound

• Some names of polyatomic anions relate to the oxygen content of the anion.

• Most end with –ite or –ate– -ate ending usually used to name an ion that has

3 oxygen atoms• Examples: sulfate (SO4

2–), nitrate (NO3–),

chlorate (ClO3–)

– 2 or less oxygen atoms have an –ite ending• Examples: sulfite (SO3

2–), nitrite (NO2–),

chlorite (ClO2–)

• Hydroxide and Cyanide are exceptions to the rules.

CH. 6 Section 3 Notes

• Compound Names and Formulas– Pg. 191-196

Naming Ionic Compounds

• Formed between cations and anions

• The names of ionic compounds consist of the names of the ions that make up the compounds.

• Names of cations include the elements of which they are composed.– Usually the name of the element

• Ex: sodium forms a sodium ion

• Names of anions are altered names of elements.– The difference is the name’s ending

• Usually with the ending –ide • Compounds with Oxygen atoms have –ate, or –ite

endings

• An ionic compound must have a total charge of zero.

• Some cation names must show their charge.– Transition metals may form several cations

(each will have a different charge).– Iron forms a +2 ion AND a +3 ion

• This is shown by placing the charge of the cation as a Roman numeral in parentheses.

– Iron (II) ion and Iron (III) ion– FeO --- Iron (II) Oxide

– Fe2O3 --- Iron (III) Oxide

Determining the charge of a transition metal cation.

• The total charge of the compound MUST be zero.– Fe2O3

• Three oxide ions have a total charge of 6-. (each oxygen ion has a charge of 2- 2-(3)=6-)

– So, the total charge of the cation must be 6+

Writing Formulas for Ionic Compounds

• If you are given the compound’s name: you can find the formula

• If you are given the formula: you can find the charge of each ion

Naming Ionic Compounds Rules• If you are given the Name:

– 1. Find the symbol of each element

– 2. Find the charge of each ion– 3. Criss-cross Method– 4. If one of the ions is a

Polyatomic Ion, put parentheses around it!!

• Calcium Chloride1. Ca, Cl

2. Ca+2 , Cl -1

3. CaCl2

4. This is not a polyatomic Ion

5. This is a polyatomic Ion

Naming Ionic Compound Rules:• If you are given the formula:

– 1. Determine if the FIRST ion is a Transition metal. If so, you MUST find it’s charge!

– 2. Find the name of each of the ions

– 3. The cation is the same as it is on the periodic table

– 4. The anion has an –ide ending (unless it is a polyatomic ion)

• AgF1. Since there is no

subscript number the charges for both must be 1.

2. Ag is Silver, F is Flourine.

3. F is in group 17 and has a -1 charge so, Ag is the cation.

4. Silver Flouride

• To find the charge of ions in a chemical formula:1. Determine the ratio of the given formula

2. Separate the ions

3. Determine each of their charges

4. If the cation is a transition metal, use the criss-cross method and then look at it’s ratio.

5. Compare to the original ratio. What ever you do to the first element, you must do the the 2nd.

CrO2

1.1:2 ratio

2.Cr O2

3.Cr +4 O-2

4.Cr2O4 Ratio is 2:4

5.Reduce the ratio to 1:2

Math Skills “Writing Ionic Formulas”

Practice Problems 1-3 Pg. 193

1.Lithium oxide1. Li+1 O-2

2. Li2O

2.Beryllium chloride1. Be+2 Cl-1

2. BeCl2

3.Titanium (III) nitride 1. Ti+3 N-3

2. TiN

Naming Covalent Compounds• For covalent compounds of two elements, numerical

prefixes tell how many atoms of each element are in the molecule.

• Numerical prefixes are used to name covalent compounds of two elements.– If there is only one atom of the first element, the name

does not get a prefix.

Number of Atoms

Prefix

1 Mono-

2 Di-

3 Tri-

4 Tetra-

5 Penta-

6 Hexa-

7 Hepta-

8 Octa-

9 Nona-

10 Deca-

• BF3

– Boron Trifluoride

• N2O4

– Dinitrogen tetroxide

Empirical Formulas• Chemical formulas that are unknown are determined by

figuring out the mass of each element in the compound.• Once the mass of each element is known, scientists can

calculate the compound’s empirical formula, or simplest formula.

• An empirical formula tells us the smallest whole-number ratio of atoms that are in a compound.

• Different compounds can have the same empirical formula.

• Molecular formulas are determined from empirical formulas.

• A compound’s molecular formula tells you how many atoms are in one molecule of the compound.

• Masses can be used to determine the empirical formula.– Convert the masses to moles. Then, find the molar

ratio to give you the empirical formula.

• Pg.196 – Math Skills “Finding Empirical Formulas”

1.One mole of an unknown compound has 36.04 g of Carbon and 6.04g of hydrogen. What is the compound empirical formula.

Section 3 Review # 1, 51. Name the following ionic

compounds, and specify the charge of any transition metal cations.

a) FeI2

a) Iron(II) Fluoride

b) MnF3

a) Manganese(III)Flouride

c) CrCl2a) Chormium(II) Chloride

d) CuS

a) Copper(II) Sulfide

5. Determine the chemical formulas for the following ionic compounds.a)Magnesium sulfate

a) MgSO4

b)Rubidium bromidea) RbBr

c)Chromium(II) fluoridea) CrF2

d)Nickel(I) carbonate a) Ni2CO3

Ch. 6 Section 4 Notes

• Organic and Biochemical Compounds – Pg. 197-204

Organic Compounds• An organic compound is a covalently

bonded compound that contains carbon.– Most contain hydrogen.– Oxygen, nitrogen, sulfur, and phosphorus can

also be found in organic compounds.

• Carbon atoms form four covalent bonds in organic compounds.

• A compound made of only hydrogen and carbon atoms is known as a hydrocarbon.– Methane, CH4 is an example

• There are four single C-H bonds• A carbon atom may never form more than 4 bonds

at a time.

• Alkanes are hydrocarbons that have only single covalent bonds.– Can have C-C bonds as well as C-H bonds– Methane is the simplest alkane

Arrangements of carbon atoms in alkanes.

• The carbon atoms in methane, ethane, and propane are all bonded in a single line because that is their only possible arrangement.

• If there are more than 3 bonded carbon atoms in a molecule, the carbon atoms do not have to be in a single line.

• IF they are in a single line: the alkane is a normal alkane, or n-alkane.

• The condensed structural formula shows how the atoms bond.

• Alkane chemical formulas usually follow a pattern.– Except for cyclic alkanes

• The # of Hydrogen atoms is always 2 more than 2x the # of carbon atoms– CnH2n+2

Alkenes have double carbon-carbon bonds.

• Hydrocarbons• Have at least one double covalent bond

between carbon atoms. C=C• Replace the –ane ending with –ene.• Simplest alkene is ethene (ethylene)

• Alcohols have hydroxyl (-OH) groups.• Made of oxygen, hydrogen, and carbon• Most alcohols end in –ol

• Alcohol and water molecules behave similarly.• Methanol and methane are alike except that one

of the hydrogen atoms is replace by a Hydroxyl group

• Alcohol molecules are attracted to each other– Liquid at room temp; HIGH boiling points

Polymers• A polymer is a molecule that is a long

chain made of smaller molecules.– Have repeating subunits– Polyethene, is a polymer that makes up

plastic milk jugs. “Poly”=many• Ethene is an alkene that has the formula C2H4.

– Polyethene means “many ethenes”– The smaller molecule that makes up the polymer is

called a monomer.

• Some polymers are natural, and others are artificial.

• Natural: Rubber, wood, cotton, wool, starch, protein, DNA, etc.

• Human-made: Plastics or Fibers

A polymer’s structure determines its elasticity.

• Chains are tangled and can slide past each other.

• When the chains are connected to each other, the polymer’s properties are different.– Some are elastic (can stretch)

• When released, returns back to its original shape.– Ex: Rubber bands

Biochemical Compounds• Essential to life, include carbohydrates, proteins,

and DNA• Can be made by living things• Carbohydrates give you energy• Proteins form important parts of your body

– Muscles, tendons, fingernails, and hair

• The DNA inside your cells gives your body info about what proteins you need.

Many carbohydrates are made of glucose.

• Carbohydrates include sugars and starches, provide energy to living things.

• Sucrose (table sugar) is made of two simple carbohydrates, glucose and fructose, bonded together.

• Starch is made of a series of bonded glucose molecules, and is a polymer.

• When you eat starchy food the enzymes in your body break down the starch.

• The glucose that is not needed is stored as glycogen, a polymer of glucose.

• When active, glycogen breaks apart into glucose molecules and gives you energy.

Proteins are complex polymers of amino acids.

• Proteins, which provide structure and function to parts of cells, are very complex.

• Made of many different molecules that are called amino acids.– Made of carbon, hydrogen, oxygen, and nitrogen.

Some contain sulfur.– 20 amino acids found in naturally occurring proteins

• The amino acids that make up a protein determine the protein’s structure and function.

• Proteins are long chains made of amino acids.– Made of thousands of bonded amino acid

molecules

DNA is a polymer that stores genetic information

• DNA is a very long molecule made of carbon, hydrogen, oxygen, nitrogen, and phosphorus.

• DNA is in the form of paired chains, or strands.– Shape of a twisted ladder, double helix.

• DNA is the information that the cell uses to make proteins.

• DNA monomers:– Adenine, thymine, cytosine, and guanine

• Pair with other DNA monomers that are attached to the opposite strand in a predictable way