1. Elements combine to form compounds.
Chapter 8.1 Notes
Elements combine to form compounds.

2. Are compounds the same as the elements that make them?
Na (Soduim) is a silver metal
Cl (Chlorine) is a poisonous gas
When combined into a compound we form NaCl… table salt which is a white crystal we sprinkle on our food to make it taste better.
Is NaCl the same as Na? Is it the same a Cl?
Are compounds the same as the elements that make them?

3. The property of a compound depends on the elements and how many of those elements we have.
Carbon (C) and Hydrogen (H) can combine in hundreds of different ways, but are they all the same?
Gasoline
Wax in candles
Cell Membranes
Propane
Plastics

4. Atoms do combine in predictable numbers.
Any compound will combine in the exact same way every time. There will always be the same number of each atom.
Ex:
Ammonia is NH3. 1 Nitrogen, 3 Hydrogen atoms.
Hydrazoic Acid is N3H. 3 Nitrogen, 1 Hydrogen

5. How do we write chemical formulas?
The steps for writing the chemical formula is pretty easy.
Step 1: Find the chemical symbols for the elements in the compound. (Use the periodic table if you can’t remember them)
Carbon = C
Lead = Pb
Oxygen = O

6. Step 2: If there is an element with only 1 of that atom in the compound you only use the symbol.
EX: 1 Carbon = C, 1 Nitrogen = N
Step 3: If there is an element with 2 or more atoms in the compound, you have to add a subscript.
A subscript is a little number written to the right and a little below the symbol.
Examples
2 Oxygen = O2
Water is H2O. (2 Hydrogen, 1 Oxygen)

7. Step 4: Now just put the symbols with their subscripts together.
EX: N + H3 = NH3 (1 Nitrogen and 3 Hydrogen atoms)
I am also ok with this written as H3N. This still means 1 Nitrogen and 3 Hydrogen atoms.
Remember, the subscript number goes with the Symbol to its left.
(H3)N or N(H3)
No subscript = 1 of that atom.
CO = 1 Carbon, 1 Oxygen

8. The number of atoms makes a big difference!
H20 is very different from H2O2.
H20 is water.. Safe to drink…
H2O2 is hydrogen peroxide.. If you drink hydrogen peroxide you will become very sick. Hydrogen peroxide is used to kill bacteria cells… it will kill your cells as well.

9. Ratios of elements… Easier than you think.
To get the ratio of the different elements in a compound you just count the number of each type of atom and put a “:” between the numbers.
EX:
Ammonia is NH3. Ratio is 1:3
Glucose is C6H12O6. Ratio is 6:12:6
DO NOT REDUCE THE NUMBERS!!!
4:2 is not the same as 2:1 in chemistry!

10. Chemical bonds hold compounds together.
Chapter 8.2 Notes
Chemical bonds hold compounds together.

11. What particle of an atom is responsible for the chemical bonds?
The nucleus of atoms do not change when compounds form.
If the nucleus contains protons and neutrons, and these don’t change, what causes chemical bonds?
The answer: Electrons. The negatively charged particles that move around an atom’s nucleus.

12. What happens to an atom when it transfers electrons?
Ions are formed when atoms gain or lose electrons.
Gaining an electron changes the atom into a negative ion. (We have an extra “–”)
Losing an electron changes the atom into a positive ion. (We lost a “-”)
So, what elements form positive ions and which form negative ions?

13. Here is where the periodic table comes into play…
Metals tend to form positive ions… which means they lose or give away electrons.
Group 1 metals lose 1 electron.
Group 2 metals lose 2 electrons.
Non-metals tend to form negative ions… which means they gain or accept electrons.
Group 17 nonmetals gain 1 electron
Group 16 nonmetals gain 2
Group 15 gains 3
Group 14 gains 4

14. How do we show the electrons of elements?
We have an easy way to represent atoms and their elements. Lewis Dot Diagrams help us to understand what electrons elements have available for bonding.
Lewis Dot Diagrams are also based on the periodic table.

15. Lewis Dot Diagrams
To make a Dot Diagram, begin by writing the chemical symbol of the element.
Hydrogen = H Oxygen = O
Next, look at the group number. The number in the one’s column equals the number of dots you write around the symbol.
Ex: Group 1 = 1 dot
Group 17 = 7 dots (the 7 is in the one’s column)

16. Now that you know how many dots, draw them around your element symbol following this rule.
Go around the symbol top, right, bottom, left. Each side needs 1 dot before you can add a second dot to the side.
Sodium has 1 dot. Na
Oxygen has 6 dots O

17. Ionic Bonds
When elements want to form positive ions, they are happy to give their electron to an element that wants to become a negative ion.
Positive ions are then attracted to negative ions (just like magnets, opposite charges attract)
The force of attraction between a positive ion and a negative ion is called and ionic bond.
In general, Ionic Bonds form between metals and nonmetals.

18. How do you name an ionic compound?
Step 1: Take the name of the metal that forms the positive ion. (sodium)
Step 2: Take the name of the nonmetal that forms the negative ion and add the ending “-ide” (Ex: chlorine becomes chlor-ide)
Step 3: Combine the names. (sodium chloride)
What is the name of KBr?

19. Covalent Bonds
Nonmetals combine with other nonmetals by sharing electron instead of gaining or losing electrons.
Sharing electrons is what forms covalent bonds.
In a covalent bond, both atoms share the electron so neither atom gains or loses an electron. Therefore no ions are formed.

20. How do we represent covalent bonds?
The most common way to show a covalent bond between 2 atoms is to draw a line connecting the atoms.
Oxygen
Covalent bond
Hydrogen Hydrogen

21. Or we an draw them by only using their chemical symbols.

22. Compounds held together by covalent bonds have a special name.
Any group of atoms held together by covalent bonds is called a molecule.
Molecules can have from 2 to many thousands of atoms in them!

23. How can we figure out how many covalent bonds an atom can form?
Lewis Dot Diagrams can help.. Or you can just memorize it.
In the Dot Diagrams, any dot/electron by itself can form a covalent bond.
2 dots together are happy and will not form a covalent bond.
2 Dots, so no covalent bonds. O
1 Dot only, these sides can form covalent bonds

24. What are Polar Covalent Bonds?
There are only 7 molecules that can share their electrons equally: H2, N2, O2, F2, Cl2, Br2 and I2.
Because the atoms in the molecule are exactly the same, there is the same number of protons in their nuclei pulling on the electrons.
All other molecules have different atoms all trying to pull the electrons close to their nucleus.

25. Oxygen, 8 Protons (++++++++)
This unequal pulling leads to polar covalent bonds. Or molecules where the electrons are not shared equally.
Oxygen, 8 Protons ( )
(+)
Hydrogen, 1 Proton
(+)
Hydrogen, 1 Proton

26. The atom that pulls harder gets a slightly negative charge
The atom that pulls harder gets a slightly negative charge. The atoms that have the electron pulled away from them get a slightly positive charge.
Water is a polar molecule. The oxygen side is slightly negative, the hydrogen side is slightly positive.

27. Chemical bonds give all materials their structure.
The way the atoms are arranged in a compound give the compound or molecule its properties.
Ionic Compounds tend to form crystals.
Covalent Molecules can have various shapes.
The shape of a molecule affects what that molecule does.
This includes the shape, smell, how the body reacts to the molecule, etc.

28. Substances’ properties depend on their bonds.
Chapter 8.3 Notes
Substances’ properties depend on their bonds.

29. Why are metals strange?
Metals do not follow the usual chemical bonding patterns. They have something called metallic bonds.
In a metallic bond, metals share their electrons equally with all the other metal atoms around them.
This lets the electrons move from atom to atom, almost like floating in the ocean.

30. What properties do metallic bonds give metals?
Metals are:
Good conductors of electricity
Good conductors of heat
Have high melting points (except for mercury)
Easily shaped by pounding
Can be drawn into wires

31. What properties do Ionic Bonds give compounds?
Ionic Compounds:
Usually a solid at room temperature
Have a high melting and boiling point
It takes a lot of energy/heat to break all the bonds holding the ions in a crystal together
This steak is being cooked on a solid slab of salt over a BBQ full of charcoal.
The block will not melt until it reaches about 900 degrees!

32. The crystals that ionic compounds form are:
Hard
Brittle
Poor conductors of electricity
One interesting thing is that ionic compounds dissolve in water very easily!
When ionic compounds are dissolved in water, the individual ions become good conductors of electricity.
Ionic compounds are poor conductors of electricity as a solid, but become good conductors when they are dissolved in water.

33. What do properties do covalent molecules have?
Covalent molecules have almost the exact opposite properties of ionic compounds.
Covalent molecules:
Melt and boil at low temperatures
The molecules stay together when dissolved in water
Are poor conductors of electricity when in water

34. Can different bonds make the same element look different?
Simple answer: Yes.
Carbon has 3 completely different forms based on the arrangement of the bonds.
Diamond
Made of each carbon bonding with 4 other carbon atoms
This makes diamond the hardest
substance on the earth.

35. Graphite
Made of each carbon bonding with only 3 other carbon atoms. Forms sheets much like a stack of paper.
This lets your pencil leave marks
on your paper.
Fullerene
Made of many carbons bonded into a soccer ball shape.