1. Chemical Bonds
Chapter 11

2. 11:1 Why Atoms Combine Learning Targets:
1. To understand molecular formation.
Success Criteria:
I can…
describe how a compound differs from the elements it is composed of.
explain what a chemical formula represents.
state a reason why chemical bonding occurs.

3. 11:1 Why Atoms Combine Compounds:
Although every thing that we see is composed of atoms of individual elements, most of what we see is not pure.
Most matter is found in the form of compounds or mixtures of compounds.

4. Compounds have properties that are different that those of their elements.
Example: Sodium (deadly) and chlorine (deadly) make table salt (salty, but not deadly).
Can you name another compound and identify the elements it is composed of?

5. Formulas:
Similar to a chemical symbol for an element, compounds have chemical formulas.
The chemical formula for any compound tells what elements it contains and the ratio of the atoms of those elements.
What are the chemical formulas for Carbon Monoxide, Water, and Carbon Dioxide?

6. Let’s look closer at the molecular formula for water:
We see in the formula that there is a number in subscript form.
Subscript, meaning “written below,” is found after the related symbol and tells us the number of that kind of atom in a single unit (molecule) of the compound.
The formula H20 tells us that in each molecule of water, there are 2 hydrogens and one oxygen.
There is a ratio of 2 hydrogen atoms to 1 oxygen.
What elements (and their ratio) make up iron (III) oxide, Fe2O3?

7. Chemically Stable Atoms:
Recall that an atom’s electron arrangement determines if it is chemically stable or if it will react.
An atom is chemically stable if its outer energy level is completely filled with electrons.
Most elements are filled when there are 8 electrons in their outer shells.
The noble gases have filled outer levels, which makes them resistant to reacting.

8. Aside from the noble gases, other elements are made of atoms containing 1-7 electrons in their outer shells.
These atoms tend to gain, lose, or share their electrons with others in an attempt to stabilize.
It is the gaining, losing, or sharing of electrons that causes chemical changes.
This allows for stabilization by creating chemical bonds.
A Chemical bond is a force that holds together the atoms in a substance.

9. Examples of bonding:
Take a look at the Dot Structures of sodium (Na) and chlorine (Cl).
Sodium has 1 electron in its outer shell, while chlorine has 7.
To stabilize, sodium gives up an electron and chlorine gains it. In the process, the two atoms form a bond.
In chlorine gas (Cl2), two chlorine atoms share electrons.
How does the bond in NaCl differ from that of Cl2?

10. By sharing or transferring electrons, the atoms achieve more stable arrangements of electrons.

11. Learning Checkpoint:
What happens to the properties of elements when atoms form compounds?
Write formulas for (A) a compound with one calcium atom and two fluorine atoms and (B) a compound with two aluminum atoms and three sulfur atoms.
Why do most elements tend to form compounds?

12. 11:2 Hazardous Compounds at Home
Learning Target: -To understand that household compounds can be hazardous. Success Criteria: I can… -describe the dangers posed by hazardous compounds in the home. -demonstrate an understanding of ways to avoid hazardous compounds or ways to use them safely.

13. 11:2 Hazardous Compounds at Home
Corrosive, Flammable, and Toxic Compounds:
Hazardous compounds contain compounds that can affect the health and safety of people.
Toxic compounds are poisonous.
Tend to be found in disinfectants, medicine, insect spray, etc.
Corrosive compounds attack and destroy metals, human tissues, and other materials.
Includes battery acid, cleaners, and bleach.
Flammable compounds include ingredients of gasoline, paint thinner, alcohol, and some aerosols.

14. Hazardous chemicals can cause a lot of problems:
Burns
Polluted resources (air, water, soil)
Cancer

15. So, what can I do? Use safer alternatives Recycle used hazardous items
Use sparingly
Pass on knowledge to others

16. 11:3 Kinds of Chemical Bonds
Learning Target: -To understand chemical bonding. Success Criteria: I can… -describe ionic bonds and covalent bonds. -identify the particles produced by ionic bonding and by covalent bonds. -distinguish between a nonpolar covalent bond and a polar covalent bond.

17. 11:3 Kinds of Chemical Bonds
Ions and Ionic Bonds:
Let’s look back at the relationship between sodium and chlorine.
Sodium gives up an electron to become more stable.
It becomes positively charged in the process. Na+
Chlorine accepts an electron to become more stable.
It becomes negatively charged in the process. Cl-
Together NaCl is formed, which is neutrally charged.

18. An ion is an atom that is charged.
Can be positive or negative.
Compounds composed of ions are called ionic compounds, which are held together by ionic bonds.
An ionic bond is the force of attraction between the opposite charges of ions in an ionic compound.

19. Molecules and Covalent Bonds:
Most atoms become more chemically stable by sharing electrons, rather then by losing or gaining them.
Look back that the example of chlorine molecules…
Chlorine molecules are not charged, but will combine with one another (via electron sharing) to be more stable.
Neutral particles formed as a result of electron sharing are called molecules.

20. A bond that forms between atoms when they share electrons is known as a covalent bond.

21. Polar and Nonpolar Molecules:
Sometimes, atoms in molecules do not share electrons equally.
Example: Water molecules are made of hydrogen and oxygen.
The oxygen atom is so much bigger than the hydrogens, the electrons that they all share spend more time with the oxygen.
This creates a partial charge.
A polar molecule is one that has a positive and a negative end.

22. Some molecules are made of atoms of similar size.
Since they share electrons equally, they are nonpolar.
A nonpolar molecule is one that does not have oppositely charged ends.

23. Extra information about bonds.
Ionic compounds:
Tend to be formed between a metal and nonmetal.
Are usually crystalline solids with high melting points.
Covalent compounds:
Tend to form between nonmetals.
Are usually liquids or gases at room temperature.

24. Learning Checkpoint: Compare ionic and covalent bonds.
What type of particle is formed by the following bonds:
Ionic B. Polar Covalent C. Nonpolar Covalent

25. 11:4 Formula Names and Compounds
Learning Target:
-To understand chemical formulas.
Success Criteria:
I can…
Explain how to determine oxidation numbers.
Write formulas for compounds from their names.
Name compounds from their formulas.
Describe hydrates and their formulas.

26. 11:4 Formula Names and Compounds
Oxidation Numbers:
By figuring out oxidation numbers, it is possible for you to determine chemical formulas.
An oxidation number is a positive or negative number assigned to an element to show its combining ability in a compound.
An oxidations number indicates how many electrons have been gained, lost, or shared when bonding with other atoms.
Label your periodic table with assigned oxidation numbers.

27. What else do we need to know about oxidation numbers?
Remember, losing electrons produces positive oxidation numbers, while gaining them produces negative ones.
Oxidation numbers tend to be those that we find in binary compounds.
A binary compound is one that is made of only 2 elements.
Examples: CO2, CO, H2O
Some elements have more than one oxidation number. This is specified in the name of the compound with a Roman numeral.
Example: In iron (III) oxide, the oxidation number of iron is 3+.
Copper (I)
Cu+
Copper (II)
Cu2+
Iron (II)
Fe2+
Iron (III)
Fe3+
Chromium (II)
Cr2+
Chromium (III)
Cr3+
Lead (II)
Pb2+
Lead (IV)
Pb4+

28. Guided Practice:
What is the formula of a compound composed of only sulfur and aluminum?
How to:
1. Write the positive element’s symbol, followed by
the negative one Al S
2. Look up oxidation numbers for each element and
write them above the symbols
Al S
3. Write in subscripts so that the sum of the oxidation
numbers is
Al2 S3
4. Check to see if the sum of the oxidation numbers is 0.
2(3+) + 3(2-) = (6+) + (6-) = 0
Solution: Al2S3

29. Practice Problems:
Write the formula for the binary compound of calcium and oxygen.
Write the formula of the binary compound of copper (II) and sulfur.

30. Solutions:
CaO
CuS

31. Naming Binary Compounds:
When naming binary compounds, use these rules:
Write the name of the first element.
Write the root of the name of the second element.
Add the ending –ide to their counterparts.
To name compounds of elements having 2 or more oxidation numbers you must first figure out the oxidation numbers of the elements.

32. Guided Practice: Problem: What is the name of CrO? Steps:
Write the name of the positive element. Chromium
If the element has more than one oxidation number, use the oxidation number of the negative element to figure out the oxidation number of the positive one. Write this number as a Roman numeral after the name of the element.
? + (2-) = 0; ? = 2+
Cr O
chromium (II)
Add the root of the name of the second element, followed by –ide.
Solution: chromium (II) oxide

33. Practice Problems:
Name the following compounds:
Li2S, MgF2, FeO, CuCl

34. Solutions: Lithium sulfide Magnesium sulfide Iron (II) oxide
Copper (I) chloride

35. Compounds With Polyatomic Ions
Some compounds, rather than being binary, are composed of more than two elements. These are called polyatomic ions.
Polyatomic ion is a positively or negatively charged group of atoms.
Again, write the positive ion first, then write the second.
If more than one of a polyatomic ion is needed, write parentheses around the group of atoms representing it.
Example: Sr(OH)2 = strontium hydroxide

36. Guided Practice: Problem: What is the formula for calcium nitrate?
Steps:
Write symbols and oxidation numbers for calcium
and the nitrate ion
Ca NO3
Write in subscripts so that the sum of the oxidation numbers is 0. Enclose the NO3 in parentheses
Ca (NO3)2
Solution: Ca(NO3)2

37. Practice Problems: What is the formula for sodium sulfate?
What is the formula for magnesium chlorate?

38. Solutions:
Na2SO4
Mg(ClO3)2

39. Some ionic compounds have water as part of their structure.
Hydrates:
Some ionic compounds have water as part of their structure.
A hydrate is a compound that has water chemically attached to its ions.
When heated, hydrates give off steam and turn into powder.

40. Learning Checkpoint: Name the following: NaI, FeI3, K2SO4, NH4Br
Write the formulas for (A) lithium sulfide (B) calcium acetate (C) barium oxide.