1. Chemical Reactions CH. 16 sec. 1: Observing Chemical Change
Read pg
Answer 1C, 2A, 2C (on pg. 657)
CH. 16 sec. 2: Describing Chemical Reactions
Read pg
Answer 1A, 2A, 3A

2. Bond…
Chemical Bond

3. Chemical Bonds

4. Chemical Bonds
Chemical bonding is the joining of atoms to form new substances.

5. Most of the things you come in contact with are combinations of atoms
plastic
salt
sugar
milk
chocolate
wood
air
Just as the 26 letters of the alphabet combine to make words, the elments combine to form compounds
water
cotton
caffeine

6. Valence Electrons
A valence electron is an electron in the outermost energy level of an atom, which causes bonding.

7. Valence Electrons Carbon 4 valence electrons Beryllium 2 valence
Oxygen
6 valence
electrons

8. Valence Electrons
*Atoms of elements in Groups 1 and 2 have the same number of valence electrons as their group number.
*Atoms of elements in Group 3-12 do not have a general rule relating their valence electrons to their group number. However, they typically have between 1 or 2 valence electrons.
*Atoms of elements in Groups have 10 fewer valence electrons than their group number. (Exception - helium atoms have only 2 valence electrons, even though they are in group 18)

9. Octet Rule
Atoms will combine to form compounds in order to reach 8 electrons in their outer energy level.

10. The Octet Rule In Action6 7
Notice how this chlorine atom has seven valence electrons, one away from eight. It will try to gain one more according to the Octet Rule. 5 + - 4 1 1 2 3
Notice how the sodium atom has one valence electron. It is this electron that it will try to get rid of according to the Octet Rule.
Where do you think chlorine finds that one electron that it needs?

11. Pop Quiz Question #1 Which shell is the valence shell? First Second
Middle
Last

12. Pop Quiz Question #2 Which element has 5 valence electrons?
A. chlorine
B. nitrogen
C. oxygen
D. hydrogen

13. Types of Chemical Bonds
Co-captain?
What does the word cooperate mean?
Coworker?
So, the prefix “co-” means . . .
share
The first type of chemical bond is called a covalent bond
Covalent bonds occur when atoms share electrons

14. COVALENT BOND Each pair of shared electrons creates a bond
Usually occurs between atoms of non-metals
Consequently, neither atom is "strong" enough to steal electrons from the other, so they have to share electrons - - - - + - + + - - - - -

15. Types of chemical bonds
The second type of chemical bond is known as ionic bonds
Ionic bonds occur when atoms transfer electrons

16. IONIC BONDS The force of attraction between oppositely charged ions.
Usually form between atoms of metals and atoms of non-metals
Consequently, the non-metal is "stronger" than the metal, and can steal electrons very easily from the metal.
Resulting compounds have a name that usually ends in –ide 1- 1+ Cl Na
Which different groups or families
of elements will most-likely
interact to create these types
of bonds? -

17. Covalent Ionic Compounds Compounds
Gases, liquids, or solids
Low melting and boiling points
Poor electrical conductors
Most are not soluble in water
Crystalline solids
High melting and boiling points
Conduct electricity when melted
Many are soluble in water

18. Pop Quiz Question #3 When sodium bonds with oxygen, they form A. Na3O2
B. Na2O3
C. Na2O
D. NaO

19. Pop Quiz Question #4
How many atoms are H2SO4?
A. 4
B. 5
C. 6
D. 7

20. how the electrons do not just stay with one ion
Metallic Bond
A force of attraction between a positively charged metal ion and the electrons in a metal
Many metal ions pass along many electrons
Many properties of metals, such as conductivity, ductility, and malleability, result from the freely moving electrons in the metal
Usually occurs between atoms of metals
Al3+ - - -
Notice
how the electrons do not just stay with one ion
This is why metals are able to conduct heat and electricity. - - - - - - - - - - -

21. Which bond is formed from the transfer of electrons?
Pop Quiz Question #5
Which bond is formed from the transfer of electrons?
A. Ionic
B. Covalent
C. Metallic

22. Writing Chemical Formulas
A chemical formula uses chemical symbols to
represent the atoms of the elements and the amount
of each atom in a chemical combination
Carbon dioxide carbon + oxygen
Carbon dioxide C + O
A subscript is a number written to the right of a chemical symbol and slightly below it. It tells how many atoms of each element are in the combination
CO2  C + O + O