The Chemical Context of Life

1
The Chemical Context of Life

• What is an element?
• The basic form of matter that cannot be broken
  down.
• What is an atom?
• The smallest unit of an element that still has
  the properties of that element.

2
What are the subatomic particles?

• Neutrons, which have no charge
• protons, which have a positive charge
• electrons which have a negative charge.

3
Characteristics of elements
Number of protons in the nucleus of the atom

• Atomic number

Number of protons number of neutrons in the
nucleus.

• Atomic mass number

An element that has a different atomic mass than
normal due to a change in the normal number of
neutrons

• Isotope

4
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.

5
Electron Energy Levels
6
Electron energy levels
2

• The 1st energy level contains how many electrons?

8

• The 2nd energy level contains how many
  electrons?

8

• The 3rd energy level contains how many
  electrons?

• An element whose valence shell is complete is
  said to be ________________________.

inert or unreactive
7
Electron Orbitals
8
Electron Configurations of First 18 Elements
9
Chemical Bonds

• Covalent bond

results from sharing a pair of electrons

• nonpolar covalent bond

equal sharing

• polar covalent bond

unequal sharing
10
What sort of covalent bonds are seen here?
11
Nonpolar Covalent bonds
Polar covalent bonds
12
Ionic Bonds

• Ion

transfer of electrons between atoms.
attraction between two oppositely charged ions

• Ionic bond

• 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 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.