1. Chemical Bonds, Equations and Reactions
Ch. 6 - p. 160 – Blue
Ch. 7 – p Blue

2. Chemical Bonds, Equations and Reactions
Objectives
1) Know what causes atoms to combine, and why atoms combine.
2) Understand Ionic and Covalent bonds.
3) Know and understand the importance of chemical reactions.
4) Know how to balance chemical equations.
5) Understand and be able to compare endothermic and exothermic reactions.
6) Understand and be able to explain the importance of inhibitors and catalysts on chemical reactions.
7) Define and be able to explain certain vocabulary words.
Atomic structure…Review…
Nucleus – What is in it?
Electron cloud – What is in it?
How do you know the number of electrons in each atom?
Periodic Table -
Arranged in order of increasing atomic numbers…

3. Electron Arrangement…
Electrons are located in the electron cloud in different energy levels.
What keeps them there?
Some are closer to the nucleus than others.
The closer they are to the nucleus, the stronger the attractive force is…
As levels get farther from the nucleus, they are at a higher energy level.
More electrons as you get farther out…
Each level can only hold a certain number of electrons.
How many electrons can be in each level?
First Five levels = 2, 8, 18, 32, 50
Electrons don’t go to the next level until the previous level is filled…
IE – 10 electrons would fill the first two levels!
How many would it take to fill the first three levels?

4. Electrons in the outer energy level = valence electrons
Valence electrons help determine characteristics of atoms.
Atoms with similar valence electron numbers have some similar characteristics.
Columns, groups on Periodic Table = same valence number
Valence electrons determine how easily, or if an atom will bond with another atom.
Atoms are more stable when energy levels are full.
Noble gases…last group…full energy levels…most stable…don’t need to bond with anything!

5. Electron Dot Diagrams = short way of showing valence electrons for an element.
shows chemical symbol in center with dots around it showing the number of valence electrons.
The number of valence electrons tells you a lot about the element:
characteristics, ability to bond!
The number of dots is shown by the group number the element is in.
Valence electrons show the ability of that atom to bond.
What is needed to fill the energy level?

6. Chemical Bond: force that holds two atoms together
Two Main Types of Bonds:
1) Ionic Bond
2) Covalent Bond
How can elements become more stable?
What are they trying to be like?
IE – Na = 11…Loses one electron…now = 10…same as Neon (10) Is it Neon? Why?
IE – Cl = 17…Gains one electron…now has 18…same as Argon (18)
Ionic Bond = transfer of electrons…losing or gaining electrons
What does losing or gaining an electron do to the charge?

7. Na+ bonding with Cl -
Protons stay the same…!!!
Changes the charge on the atom…
Ion = atom with a charge
Losing an electron gives the atom a positive charge = positive ion
Gaining an electron gives the atom a negative charge = negative ion
Now…positive Na & negative Cl are attracted to each other…(picture)
This attraction is a chemical bond called an ionic bond.
Sodium Chloride = table salt
Compound = pure substance that contains two or more elements
If there is more than one electron that is released by an atom, it is noted by the superscript.
The electrons can go to one atom, or two atoms.

8. Some electrons have to lose or gain too many electrons.
2) Covalent Bond
Some electrons have to lose or gain too many electrons.
There isn’t enough energy in the protons to do this.
How do these atoms bond?
They share electrons between outer energy levels…this is a covalent bond. (Draw Picture…)
IE – H & H…each has 1 electron
How many do they want?
Covalent…2 together.
IE – H & H & 0
Each has how many?
Covalent…each has what they need
Covalent Bond = sharing of electrons
Covalent bonds form a neutral particle = molecule.

9. “How To” Diagram
Create a “How To” diagram for an ionic bond and a Covalent Bond.
Start with how to create an Electron Dot Diagram
Use Na + Cl for an ionic bond
Use H + Cl for a Covalent bond

10. Complete the chemical bonds
Ionic Bonds
Na + Cl
Ca + Cl
K + Br
Ca + Cl + Cl
K + N + O + O + O
Mg + O
Ag + Cl
Make up 5 of your own
Covalent Bonds
H + H
F + F
O + C + O
F + F + C + F + F
H + Cl
S + O + O + O
N + O + N
Make up 5 of your own

11. Polar & Nonpolar molecule:
Do atoms always share electrons equally?
IE – H20… NO they don’t…
Oxygen attracts the electrons more than Hydrogen.
Electrons spend more time on Oxygen than Hydrogen.
This causes the oxygen end of the molecule to have a slight negative charge, and the hydrogen end to have a slight positive charge.
Polar Molecule: when atoms do not share electrons equally, resulting in a charged particle.
Nonpolar: bonds are between atoms of the same element.
IE – Nitrogen…2 nitrogen molecules…

12. Complete a lab write up for today’s activity
Include:
Question
Hypothesis
Materials
Procedure
Variables (Independent, Dependent, Control)
Results: Data table
Conclusion

13. Why use symbols for elements? easy, shorter to write…understandable…
Chemical Shorthand
Why use symbols for elements?
easy, shorter to write…understandable…
Chemical Formulas
allows scientists to communicate and share research
shorter to write
IE – CO2 = carbon dioxide
“2” = subscript…”sub = below, “script” = write
Therefore, “2” means two oxygen atoms
If there is no number = 1 atom of that element
Formula = combination of chemical symbols of the elements that tells what elements are present in a molecule, and how many atoms of each element are present

14. Balancing Equations
A chemical equation describes what happens in a chemical reaction.
The equation identifies:
reactants (starting materials)
products (resulting substance)
the formulas of the participants
the phases of the participants (solid, liquid, gas)
the amount of each substance.
Balancing a chemical equation refers to establishing the mathematical relationship between the quantity of reactants and products.

15. Steps to Balancing a Chemical Equation
C3H8 + O2  CO2 + H2O
Write the unbalanced equation.
Count the number of atoms in each side (reactants and products) element by element.

16. Steps to Balancing a Chemical Equation C3H8 + O2  CO2 + H2O
3. Start with an element found in one compound on each side of the equation. Change the coefficients (#’s in front of the compound) so that the number of atoms of the element is the same on each side of the equation.
Repeat with all other elements in the chemical equation.
Check your work.
C3H8 + 5O2  3CO2 + 4H2O

17. Chemical Reactions = CH.7 – p.188 Blue
process in which chemical changes occur
IE – rotten eggs, campfire, tree leaves changing color, rust…
Matter can undergo two kinds of changes
1) Physical change:
= affect its physical properties such as size, shape or its state of matter.
IE – water frozen to ice…liquid to solid…but it is still water
2) Chemical change:
= results in the formation of a new substance that has different properties from the original substance
IE – rust on a car, egg is fried, leaves turn colors
Can anything go through both changes?
Yes!
IE - Newspaper…crumple it up, after a long time it changes color, and then you could burn it!

18. Two kinds of reactions:
When bonds are broken, or changed, energy is involved.
Some bonds are broken, while others are formed.
Therefore, there will always be a change in energy.
REMEMBER: Energy is not created or destroyed, it just changes form.
Energy will either be released, or absorbed, during a chemical reaction.
If energy is absorbed, this is called an endothermic reaction. (Cools down)
If energy is released, this is called an exothermic reaction. (heats up)

19. Make a list of Physical & Chemical Changes
Physical Changes:
Melting of ice
Drying of wet clothes
List 6 more physical changes
Draw a picture for 4 of them…
Chemical Changes
Rusting of iron
Darkening of apples
List 6 more chemical changes
Draw a picture for 4 of them…