1. The Chemical Context of Life
Chapter 2

2. The Chemical Context of Life
What is an element?
The basic form of matter that cannot be broken down
What is a compound?
Two or more different elements combined in a fixed ratio
What is an atom?
The smallest unit of an element that still has the properties of that element.

3. Subatomic particles neutrons protons electrons no charge
found in the nucleus
mass of 1 amu
protons
positive charge
electrons
negative charge
found outside the nucleus
little mass

4. Characteristics of Elements
Atomic number: Number of protons in the nucleus of an atom
Mass number: Number of protons plus the number of neutrons in the nucleus
Isotope: An element that has a different mass than normal due to a change in the normal number of neutrons

5. Electrons Located outside of the nucleus
Unless otherwise indicated the number of electrons is the same as the number of protons
Potential energy of electrons increases as their distance from the nucleus increases
Electrons orbit the nucleus in energy levels

6. Electron Energy Levels

7. Electron Energy Levels
The first energy level contains how many electrons? 2
The second energy level contains how many electrons? 8
The third energy level contains how many electrons?
An element whose valence shell is complete is said to be what?
Inert or unreactive

8. Electron Orbitals

9. Electron Configurations of First 18 Elements

10. Chemical Bonds Covalent bond Non-Polar Covalent bond
Sharing of a pair of valence electrons by two atoms
Non-Polar Covalent bond
Equal sharing of electrons
Polar Covalent bond
Unequal sharing of electrons

11. What sort of covalent bonds are seen here?

12. Ionic Bonds Ion - transfer of electrons between atoms
Ionic bond – attraction between two oppositely charged ions
Cation – positively charged ion (lost electron)
Anion – negatively charged ion (gained electron)

13. Hydrogen Bonds Oxygen is one of the most electronegative elements
In a water molecule electronegative oxygen “hogs” electrons.
This “hogging” of electrons results in which type of bond between oxygen and hydrogen within the water molecule?
Polar covalent

14. Hydrogen Bond
Hydrogen bonds occur between two polar molecules, or between different polar regions of one large macro- molecule.
One “relatively” negative region is attracted to a second “relatively” positive region.

15. Van der Waals Interactions
Weak attractions that occur when atoms and molecules are very close together
May occur in regions of a single large molecule such as a protein

16. Shape and function
Molecular shape determines how molecules recognize and respond to one another
Molecules with shapes similar to brain signal molecules can affect mood and pain perception
Ex: morphine and heroin mimic endorphins in the brain

19. Chemical Reactions Starting materials are known as
reactants
Ending materials are known as
products
Matter can only be ______________ not created or ______________
When forward and reverse reactions occur at the same rate, ______________ has been established

20. Ionic bond, cation, anion