Chapter 2: Atoms and Molecules of Ancient EarthLife requires about 25 elements

carbon (C) oxygen (O) hydrogen (H) nitrogen (N)

Chapter 2: Atoms and Molecules of Ancient EarthAtoms and molecules:

*Atomic number

*Atomic weight

The energy levels of electrons:

*electrons vary in energy

Energy

Potential energy

44

222323

111111

11HeHe NaNa HH

Atoms with full shells are chemically stable, and won’t react easily with other atoms.

Chapter 2: Atoms and Molecules of Ancient Earth

Electron configuration and chemical properties:

*chemical behavior due to electrons

Element Symbol Atomic Number

# Electrons normally gained (+) or lost (-)

Aluminum Al 13 -3

Argon Ar 18 0

Beryllium Be 4 -2

Boron B 5 -3

Carbon C 6 + or – 4

Chlorine Cl 17 +1

Fluorine F 9 +1

Helium He 2 0

Hydrogen H 1 -1

Lithium Li 3 -1

Magnesium Mg 12 -2

Neon Ne 10 0

Nitrogen N 7 +3

Oxygen O 8 +2

Phosphorus P 15 +3

Silicon Si 14 + or – 4

Sodium Na 11 -1

Sulfur S 16 +2

•Recall: Atomic Number is the number of protons found in nucleus.

Atoms combine by chemical bonding to form molecules

*Chemical behavior depends on valence electrons

*Covalent bond

Examples:Covalent bond

Double Covalent

bond

Chapter 2: Atoms and Molecules of Ancient Earth

Atoms combine by chemical bonding to form molecules:

Another example:

Compound

*electronegativity

nonpolar covalent bond

polar covalent bond

Example:

H2O - water

Chapter 2: Atoms and Molecules of Ancient Earth

Positive ions are missing electrons, and therefore have a positive charge (HH++ Li Li++ Na Na++ K K++)

Negative ions have extra electrons, thus a negative charge (FF-- ClCl-- Br Br-- I I--)

• Ions - Atoms in which number of electrons does not equal number of protons.

Atoms combine by chemical bonding to form molecules:

*ionic bonds

11 17

*ion

*cation

*anion

ionic compounds or salts

Chapter 2: Atoms and Molecules of Ancient Earth

• Covalent vs. ionic bond - draw

Atoms combine by chemical bonding to form molecules:

*bonding between molecules

Hydrogen bonds:

Chapter 2: Atoms and Molecules of Ancient Earth

Polarity of water:

Water: what’s the big deal?

*Hydrogen bonding

water transport in plantsadhesion

*Cohesion

Chapter 2: Atoms and Molecules of Ancient Earth

Water is the solvent of life

*solution

*solvent *solute *aqueous solution

*polar and ionic molecules can be dissolved in water

Chapter 2: Chemical Components of CellsHydrophilic and hydrophobic substances

*hydrophilic

*hydrophobic

Chapter 2: Chemical Components of CellsHydrophilic and hydrophobic substances

*hydrophilic

*hydrophobic

The dissociation of water molecules

H2O H+ + OH-

Acids and bases*acid

*base

Chapter 2: Chemical Components of Cells

The pH scale