1. Atoms are the basic units of matter and consist of protons, neutrons, and electrons. Elements are pure substances made of only one type of atom, while isotopes are atoms of the same element that differ in neutron number. 2. Theories of atomic structure have evolved over time from Democritus' idea of indivisible atoms to the current model of atoms having a small, dense nucleus surrounded by orbiting electrons. Key contributors included Thomson, Rutherford, Bohr, and Chadwick. 3. Water has an indispensable role in biological systems due to its ability to dissolve many polar and ionic substances via hydrogen bonding. About 75-85% of living cells are made up of water.

1. The Chemistry of Life
Chapter 2
Lesson 1.1

2. The Nature of Matter (In a Nutshell)
• Atom: Basic unit of matter…consist of
• Proton: Positively charged
• Neutron: No charge
• Electron: Negatively charged
• Element: Pure substance that contains only one type of atom
• Isotope: Atoms of the same element that differ in their number of
neutrons
Located in the nucleus

3. Atom Stuff
• The number of protons will
always equal the number of
electrons UNLESS the atom is
charged (ionic)
• Number on periodic table
represents the number of
protons (and therefore
electrons too) contained in
one atom

4. Atomic Theory
• What is an atom? In 430 BCE, Democritus proposed that all matter
consisted of small pieces that were indivisible
• He called them atomos (= “uncuttable”)
• Atom: The smallest particle that can still be considered an element
Lesson 1 Atomic Theory

5. History of Atomic Theory
John Dalton’s Theory (1600s):
1. All elements consist of atoms that cannot be divided.
2. All atoms of the same element are exactly alike and have the same
mass.
3. An atom of one element cannot be changed into an atom of
another element.
4. Compounds are formed when atoms of more than one element
combine in a specific ratio.
Lesson 1 Atomic Theory

6. History of Atomic Theory
• JJ Thomson (1897) discovered atoms contain negatively charged particles –
now called electrons
• Proposed that atoms contained electrons scattered in a ball of positive
charges
• “Plum Pudding Model”
Lesson 1 Atomic Theory

7. History of Atomic Theory
• Ernest Rutherford (1911)
discovered that atoms are
mostly empty space
• Also discovered the nucleus:
the dense positively charged
center
• Named the positive particles
in the nucleus of the atom
“protons”
Lesson 1 Atomic Theory

8. History of Atomic Theory
• Niels Bohr (1913)
revised Rutherford’s
model
• Suggested that
electrons move in
orbits around the
nucleus
• Each electron orbit
has a fixed energy
Lesson 1 Atomic Theory

9. History of AtomicTheory
• Cloud Model (1920s)
• Electrons found to move rapidly
through a cloudlike region –not
through specific orbits as Bohr
suggested
Lesson 1 Atomic Theory

10. History of Atomic Theory
• James Chadwick (1932) named
another particle in the atom: the
neutron.
• Neutron: Has no electric charge
Lesson 1 Atomic Theory

11. Bonding
• Ionic bond: Formed when one or more electrons are transferred
from one atom to another (ions, woohoo!)
• Covalent bond: Formed when atoms share one electron from each
atom (molecules, woohoo!)
• Two types: Polar and Nonpolar

12. Polar and Nonpolar Covalent Bonds
Nonpolar Bonds: Equal share of
electrons
Polar Bonds: Unequal share of
electrons

13. A Special [Hydrogen] Bond (Water!)
• Hydrogen Bond: Formed by the attraction between a hydrogen atom
with partial positive charge and another atom with partial negative
charge …problem is, they are very weak

14. The Importance of Being Water
Ch. 2
Topic 1.2

15. The Importance of Being Water
• Water has an indispensable role as the universal solvent in biological
systems
• It is the single most abundant component of cells and organisms
• About 75-85% of a cell by weight is water
• Its chemical characteristics make water indispensable for life

16. The Water Molecule
• Water molecules are polar (unequal,
remember?)
• This means their charges are unevenly
distributed
• What sort of bonding is happening here?

17. HYDROGEN BONDING!

18. ~Forces~ in Water
• Water is characterized by an extensive network of hydrogen-bonded
molecules, which make it cohesive  High surface tension
• Cohesion: Attraction between molecules of same substance
• Adhesion: Attraction between molecules of different substance

19. Water as a Solvent
• A solvent is a fluid in which another
substance, the solute, can dissolve
• Water is able to dissolve a large
variety of substances, due to its
polarity
• Most of the molecules in cells are
also polar and so can form hydrogen
bonds, or ionic bonds with water

20. Quick Review on pH
• pH: measure of the hydrogen ion concentration of a solution
• pH = “Potential of Hydrogen”
• High pH (7-14) vs Low pH (0-14)
AKA Basic

21. More pH Stuff