2. Basic Chemistry

3. Molecules and Compounds
Molecule – two or more like atoms combined chemically. Ex: H (atom)+H (atom) H2 (molecule)
Compound – two or more different atoms combined chemically
Ex: 4H + C = CH4 (methane)
Chemical equation
Molecular formula

4. Chemical bonds and chemical reactions
Atoms are united by chemical bonds.
A chemical bond is not a physical structure. It is energy relationship between the electrons of the reacting atoms
Chemical reactions occur whenever atoms combine with or dissociate from other atoms.

5. Driving force for bonds
Chemical bonds make atoms more stable than they are if non-bonded
Bond formation involves changes in the electrons on two atoms.
Electron transfer
Electron sharing

6. Electron shells Atomic number = number of Electrons
Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.
Electron shells determine how an atom behaves when it encounters other atoms.
Seven electron shells in any atom.
The only electrons that are important in bonding are those in the atom’s outermost shell or the valence shell.

7. Electron shells
Nucleus
1st shell
2nd shell
3rd shell

8. Noble gases provide clues

9. The Octet Rule: Happiness is a filled shell
All elements strive to become a noble gas, at least as far as the electrons are concerned.
Filling the outer shell – 8 electrons
Achieve this by adding electrons
Or taking them away

10. The valence shell
Valence electrons:
Only the electrons in the outer shell matter
Core electrons:
Filled inner shells don’t participate
Filled valence shells means no bond formation – noble gases
Unfilled shells mean reactivity

11. Types of chemical bonds
Atoms dissociate from other atoms when chemical bonds are broken
Chemical bonds: ionic, covalent, hydrogen bonds

12. Chemical Bonds – Ionic Bonds
Ionic Bonds – gain or loose electrons
Form when electrons are transferred from one atom to another
Ions
Charged particles
Anions - negative
Cations - positive
Either donate or accept electrons

13. ionic bond  A chemical bond in which atoms of opposite charge are held together by electrostatic attraction.

14. Chemical Bonds – Covalent Bond
Covalent Bonds – share electrons
Atoms become stable through shared electrons
Single covalent bonds share one electron
Double covalent bonds share two electrons
Figure 2.6c

15. Polarity Covalent bonded molecules Some are non-polar Some are polar
Electrically neutral molecule
Some are polar
Have a positive and negative side
Figure 2.7

16. Chemical Bonds – Hydrogen Bond
Hydrogen bonds
Weak chemical bonds
Hydrogen is attracted to negative portion of polar molecule
Provides attraction between molecules

17. Hydrogen bond
Attraction between (+) end of polar molecule with the (-) end of another polar molecule

18. Patterns of Chemical Reactions
Synthesis reaction (A+BAB)
Atoms or molecules combine to form a larger, more complex molecule.
Energy is absorbed for bond formation
Synthesis reactions underlie all anabolic (constructive) activities occuring in body cells.
Important for growth and repairing process.

19. Patterns of Chemical Reactions
Decomposition reaction (ABA+B)
Molecule is broken down into smaller or simpler molecules.
Synthesis reactions in reverse.
Bonds are always broken and chemical energy is released.
Decomposition reactions underlie all catabolic (destructive) processes in body cells (Ex: digestion and glycogen breakdown to release glucose.

20. Exchange reactions Patterns of Chemical Reactions
AB + CAC+B and AB + CD  AD+CB
Involves both synthesis and decomposition reactions
Bonds are both made and broken
Molecules switch and different molecules are made
Ex: ATP reacts with glucose and transfers its end phosphate group to glucose.

21. Synthesis and Decomposition Reactions

22. Exchange reactions