2. Chapter Sixteen: Compounds
16.1 Chemical Bonds and Electrons
16.2 Chemical Formulas
16.3 Molecules and Carbon Compounds

3. 16.1 Chemical Bonds and Electrons
A chemical bond forms when atoms transfer or share electrons.
A covalent bond is formed when atoms share electrons.

4. 16.1 Chemical formulas
A molecule’s chemical formula tells you the ratio of atoms of each element in the compound.

5. 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.

7. 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.

8. 16.1 Reactivity
In chemistry, reactive means an element readily forms chemical bonds, often releasing energy.
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.

10. 16.1 Valence electrons
Chemical bonds are formed only between the electrons in the highest unfilled energy level.
These electrons are called valence electrons.

12. 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?

13. 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.

14. 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 (CO2) are double bonds because each bond involves 2 electrons.

15. 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?

16. Chapter Sixteen: Compounds
16.1 Chemical Bonds and Electrons
16.2 Chemical Formulas
16.3 Molecules and Carbon Compounds

17. 16.2 Chemical Formulas and Oxidation Numbers
All compounds have an electrical charge of zero (they are neutral).
An oxidation number indicates the charge on the atom (or ion) when electrons are lost, gained, or shared in chemical bonds.

18. 16.2 Oxidation Numbers
A sodium atom always ionizes to become Na+ (a charge of +1) when it combines with other atoms to make a compound.
Therefore, we say that sodium has an oxidation number of 1+.
What is chlorine’s oxidation number?

20. 16.2 Ionic bonds
On the periodic table, strong electron donors are the left side (alkali metals).
Strong electron acceptors are on the right side (halogens).
The further apart two elements are on the periodic table, the more likely they are to form an ionic compound.

21. As heat energy is added to ice, the temperature increases until it reaches 0°C.
Then the temperature stops increasing.
As you add more heat, more ice becomes liquid water but the temperature stays the same.
This is because the added energy is being used to break the intermolecular forces and change solid into liquid.
Once all the ice has become liquid, the temperature starts to rise again if more energy is added.

22. 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.

23. 16.2 Oxidation numbers and chemical formulas
Remember, the oxidation numbers for all the atoms in a compound must add up to zero.

24. As heat energy is added to ice, the temperature increases until it reaches 0°C.
Then the temperature stops increasing.
As you add more heat, more ice becomes liquid water but the temperature stays the same.
This is because the added energy is being used to break the intermolecular forces and change solid into liquid.
Once all the ice has become liquid, the temperature starts to rise again if more energy is added.

25. 16.2 Oxidation numbers
Some periodic tables list multiple oxidation numbers for most elements.
This is because more complex bonding is possible.

27. Predict the chemical formula of this compound.
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.

28. Solving Problems Looking for: Given Relationships: Solution
…formula for a binary compound
Given
… Fe3+ and O2–
Relationships:
Write the subscripts so that the sum of the oxidation numbers equals zero.
Solution
Two iron atoms = 2 × (3+) = 6+
Three oxygen atoms = 3 × (2–) = 6–

29. 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.”

30. 16.2 Some polyatomic ions

31. Al3+ combines with sulfate (SO4)2– to make aluminum sulfate.
Solving Problems
Al3+ combines with sulfate (SO4)2– to make aluminum sulfate.
Write the chemical formula for aluminum sulfate.

32. Solving Problems Looking for: Given Relationships: Solution
…formula for a ternary compound
Given
… Al3+ and SO42–
Relationships:
Write the subscripts so that the sum of the oxidation numbers equals zero.
Solution
Two aluminum ions = 2 × (3+) = 6+
Three sulfate ions = 3 × (2–) = 6–

33. 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 to show the shape and arrangement of atoms in a molecule.

34. 16.3 Structural diagrams
Two substances have the same formula as aspirin, but not its pain relieving properties.

35. 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.

36. 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.

37. 16.3 Carbohydrates
Carbohydrates are energy-rich compounds made from carbon, hydrogen, and oxygen.
Carbohydrates are classified as either sugars or starches.

38. 16.3 Carbohydrates
Carbohydrates are mainly composed of carbon, hydrogen, and oxygen in a ratio of about 1:2:1.
Glucose, C6H12O6, is a simple sugar.
Table sugar is a carbohydrate called sucrose.

39. 16.3 Carbohydrates
Starches are long chains of simple sugars joined together.
Cellulose is the primary molecule in plant fibers, including wood.

40. 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.

41. 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.

42. 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?

43. 16.3 Enzymes Enzymes are proteins.
An enzyme is a type of protein that cells use to speed up chemical reactions in living things.

44. 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.

45. 16.3 Nucleic Acids
Nucleic acids are compounds made of long, repeating chains called nucleotides.
Each nucleotide contains:
a sugar molecule
a phosphate molecule, and
a base molecule.

46. 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.

47. 16.3 DNA Each side of the ladder is made of:
5-carbon sugars called deoxyribose
and phosphate groups.

48. 16.3 DNA
There are four nitrogen bases in two matched pairs.