COMPOUNDS Chapter Sixteen: Compounds 16.1 Chemical Bonds and Electrons 16.2 Chemical Formulas 16.3 Molecules and Carbon Compounds.
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COMPOUNDS
Chapter Sixteen: Compounds 16.1 Chemical Bonds and Electrons 16.2 Chemical Formulas 16.3 Molecules and Carbon Compounds
Chapter 16.1 Learning Goals Infer the relationship between the number of valence electrons and the behavior of atoms.
Compare and contrast ionic and covalent bonding.
Draw Lewis diagrams to represent the valence electrons of atoms.
Investigation 16A Chemical Bonds
Key Question: Why do atoms form chemical bonds?
16.1 Chemical Bonds and Electrons A
chemical bond
forms when atoms transfer or share electrons. A
covalent bond
formed when atoms share electrons.
is
16.1 Chemical formulas A molecule’s
chemical formula
you the ratio of atoms of each element in the compound.
tells
16.1 Ionic bonds Not all compounds are made of molecules.
Ionic bonds
are bonds in which electrons are transferred from one atom to another.
Sodium and chlorine form an ionic bond because the positive sodium ion is attracted to the negative chloride ion.
16.1 Why chemical bonds form It takes energy to separate atoms that are bonded together.
The same energy is released when chemical bonds form.
Atoms form bonds to reach a lower energy state.
16.1 Reactivity In chemistry,
reactive
element readily forms chemical bonds, often releasing energy.
means an Some elements are more reactive than others.
The closer an element is to having the same number of electrons as a noble gas, the more reactive the element is.
16.1 Valence electrons Chemical bonds are formed only between the electrons in the highest unfilled energy level. These electrons are called
valence electrons
.
16.1 Valence electrons and the periodic table Going from left to right across a period each new element has one more valence electron than the one before it .
How many valence electrons does nitrogen have?
16.1 Valence electrons and the periodic table Oxygen combines with one beryllium atom because beryllium can supply two valence electrons to give oxygen its preferred number of 8.
16.1 Valence electrons and the periodic table Carbon has four valence electrons. Two oxygen atoms can bond with a single carbon atom, each oxygen sharing two of carbon’s four valence electrons. The bonds in carbon dioxide (CO 2 ) are 2 electrons.
16.1 Lewis dot diagrams A clever way to keep track of valence electrons is to draw
Lewis dot diagrams
. A dot diagram shows the element symbol surrounded by one to eight dots representing the valence electrons.
What is the dot structure for nitrogen?
Chapter Sixteen: Compounds 16.1 Chemical Bonds and Electrons 16.2 Chemical Formulas 16.3 Molecules and Carbon Compounds
Chapter 16.2 Learning Goals Use the periodic table to make predictions about whether atoms will most likely form ionic or covalent bonds.
Describe how oxidations numbers can be used to write chemical formulas of compounds.
Correctly name chemical compounds.
Investigation 16B Chemical Formulas
Key Question: Why do atoms combine in certain ratios?
16.2 Chemical Formulas and Oxidation Numbers All compounds have an electrical charge of zero (they are neutral).
An
oxidation number
in chemical bonds.
indicates the charge on the atom (or ion) when electrons are lost, gained, or shared
16.2 Oxidation Numbers A sodium atom always ionizes to become Na combines with other atoms to make a compound. + (a charge of +1) when it Therefore, we say that sodium has an oxidation number of 1 + .
What is chlorine’s oxidation number?
16.2 Ionic bonds On the periodic table, strong
electron donors
are the left side (alkali metals). Strong
electron acceptors
right side (halogens). are on the The further apart two elements are on the periodic table, the more likely they are to form an ionic compound.
16.2 Covalent bonds Covalent compounds form when elements have roughly equal tendency to accept electrons. Elements that are both nonmetals and therefore close together on the periodic table tend to form covalent compounds.
16.2 Oxidation numbers and chemical formulas Remember, the oxidation numbers for all the atoms in a compound must add up to
zero
.
16.2 Oxidation numbers Some periodic tables list multiple oxidation numbers for most elements. This is because more complex bonding is possible.
Solving Problems Iron and oxygen combine to form a compound. Iron (Fe) has an oxidation number of 3+. Oxygen (O) has an oxidation number of 2–. Predict the chemical formula of this compound.
Solving Problems 1.
Looking for: … formula for a binary compound 2.
Given … Fe 3+ and O 2– 3.
Relationships: Write the subscripts so that the sum of the oxidation numbers equals zero.
4.
Solution Two iron atoms = 2 × (3+) = 6+ Three oxygen atoms = 3 × (2–) = 6–
Solving Problems
Fe
3+ 3
x O
2 2
=
6
Solving Problems
Fe
3+
+ Fe
3+
=
+6
O
2-
+ O
2-
+ O
2 +6
=
-6 -6 0
Solving Problems
Fe
3+ 2
O
2 3
16.2 Polyatomic ions Compounds can contain more than two elements. Some of these types of compounds contain
polyatomic ions
. A polyatomic ion has more than one type of atom. The prefix
poly
means “many.”
16.2 Some polyatomic ions
Solving Problems Al 3+ combines with sulfate (SO 4 ) 2– make aluminum sulfate. to Write the chemical formula for aluminum sulfate.
Solving Problems 1.
Looking for: … formula for a ternary compound 2.
3.
Given … Al 3+ and SO 4 2– Relationships: Write the subscripts so that the sum of the oxidation numbers equals zero.
4.
Solution Two aluminum ions = 2 × (3+) = 6+ Three sulfate ions = 3 × (2–) = 6–
Solving Problems
Al
3+ 2
(SO 4 )
2 3
Chapter Sixteen: Compounds 16.1 Chemical Bonds and Electrons 16.2 Chemical Formulas 16.3 Molecules and Carbon Compounds
Chapter 16.3 Learning Goals Explain the significance of carbon in the structure of many different molecules.
Describe the importance of carbon to living organisms.
Compare and contrast the structure and function of carbohydrates, lipids, proteins, and nucleic acids.
Investigation 16C Carbon and its Chemistry
Key Question: What are some common molecules that contain carbon?
16.3 Molecules and Carbon Compounds In addition to the elements from which it is made, the shape of a molecule is also important to its function and properties. We use
structural diagrams
shape and arrangement of atoms in a molecule.
to show the
16.3 Structural diagrams Two substances have the same formula as aspirin, but not its pain relieving properties.
16.3 The chemistry of carbon Carbon molecules come in three basic forms: straight chains, branching chains, and rings. All three forms are found in important biological molecules.
16.3 Organic compounds
Organic chemistry
is the branch of chemistry that specializes in carbon compounds, also known as organic molecules.
Plastic, rubber, and gasoline are important carbon compounds.
Scientists classify the organic molecules in living things into four basic groups: carbohydrates, proteins, fats, and nucleic acids.
16.3 Carbohydrates
Carbohydrates
are energy-rich compounds made from carbon, hydrogen, and oxygen.
Carbohydrates are classified as either
sugars
or
starches
.
16.3 Carbohydrates Carbohydrates are mainly composed of carbon, hydrogen, and oxygen in a ratio of about 1:2:1. Glucose, C 6 H 12 O 6 , is a simple sugar.
Table sugar is a carbohydrate called
sucrose
.
16.3 Carbohydrates Starches are long chains of simple sugars joined together.
Cellulose
is the primary molecule in plant fibers, including wood.
16.3 Lipids Like carbohydrates,
lipids
are energy rich compounds made from carbon, hydrogen, and oxygen whose ratio is much less than 1:2:1.
Lipids include fats, oils, and waxes.
16.3 Lipids A typical fat molecule has a two part structure: glycerol fatty acid chains
16.3 Saturated or unsaturated fat?
In a
saturated fat
, carbon atoms are surrounded by as many hydrogen atoms as possible.
An
unsaturated fat
has fewer hydrogen atoms than it could have.
16.3 Proteins
Proteins
are basic molecular building blocks of cells and all parts of animals.
Proteins are among the largest organic molecules.
Why is the shape of a protein important?
16.3 Enzymes
Enzymes
proteins. are An enzyme is a type of protein that cells use to speed up chemical reactions in living things.
16.3 Proteins Protein molecules are made of smaller molecules called amino acids. Your cells combine different amino acids in various ways to make new and different proteins.
16.3 Nucleic Acids
Nucleic acids
of long, repeating chains called
nucleotides .
are compounds made Each nucleotide contains: 1.
2.
a sugar molecule a phosphate molecule, and 3.
a base molecule .
16.3 DNA and nucleic acids DNA is a nucleic acid .
A DNA molecule is put together like a twisted ladder.
This model shows a short piece of the flattened DNA ladder.
A DNA molecule is usually twisted and much longer.
16.3 DNA Each side of the ladder is made of: 5-carbon sugars called
deoxyribose
and
phosphate
groups.
16.3 DNA There are four nitrogen bases in two matched pairs .
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