1. Organisms are composed of Elements in combinations called compounds
Elements cannot be broken down by ordinary chemical means
Atoms are unique building blocks for each element
Compound
A substance consisting of two or more different elements combined in a fixed ratio
(C6H12O6)

2. Atoms consist of protons, neutrons and electrons
Three important subatomic particles:
Neutrons
No charge in the nucleus
1 atomic mass unit (amu)
Protons
Positive charge, in the nucleus
1 amu
Electrons
Negative charge , orbit nucleus
Zero amu
Equal in number to protons in atom
Atoms of different elements contain different numbers of subatomic particles
Compare hydrogen, helium and lithium

3. Proton
Neutron
Electron
Hydrogen (1H)
Deuterium (2H)
Tritium (3H)

4. Atomic Number and Atomic Mass
Atomic number = number of protons in nucleus
Mass number = mass of protons and neutrons
Mass numbers of atoms of an element: are not all identical
Isotopes: Structural variations of elements; differ in the # of neutrons they contain

5. Isotopes Hydrogen (H) Helium (He) Lithium (Li) Proton Neutron Electron
Figure 2.2

6. Radioactive Isotopes can Help or Harm Us

7. The distribution of electrons determines an atoms chemical properties
Electrons occupy up to seven electron shells (energy levels) around nucleus
Octet rule: Except for the first shell which is full with two electrons, atoms interact in order to have eight electrons in their outermost energy level (valence shell)
Stable and unreactive elements have their valence shell fully occupied
Reactive elements lack a full valence shell and tend to gain, lose, or share electrons (form bonds) with other atoms to achieve stability

8. (a) Chemically inert elements
Valence shell complete 8e 2e 2e
Helium (He)
Neon (Ne)

9. (b) Chemically reactive elements
Valence shell incomplete 4e 1e 2e
Hydrogen (H)
Carbon © 1e 6e 8e 2e 2e
Oxygen (O)
Sodium (Na)

10. Covalent Bonds join atoms into molecules through electron sharing
Formed by sharing of two or more valence shell electrons
Allows each atom to fill its valence shell at least part of the time
Sharing of electrons may be equal or unequal
Equal sharing produces electrically balanced nonpolar molecules
CO2
Unequal sharing by atoms with different electron-attracting abilities produces polar molecules
H2O
Atoms with six or seven valence shell electrons are electronegative, e.g., oxygen

11. + Reacting atoms Resulting molecules or Hydrogen atoms Carbon atom
Molecule of
methane gas (CH4)
(a) Formation of four single covalent bonds:

12. + Reacting atoms Resulting molecules or Oxygen atom Oxygen atom
Molecule of
oxygen gas (O2)
(b) Formation of a double covalent bond:
Figure 2.7b

13. + Reacting atoms Resulting molecules or Nitrogen atom Nitrogen atom
Molecule of
nitrogen gas (N2)
(c) Formation of a triple covalent bond:.

14. Ionic bonds are attractions between ions of opposite charge
Ions are formed by: transfer of valence shell electrons between atoms
Anions (– charge): have gained one or more electrons
Cations (+ charge): have lost one or more electrons
Attraction of opposite charges: results in an ionic bond – +
Sodium atom (Na)
Chlorine atom (Cl)
Sodium ion (Na+)
Chloride ion (Cl–)
Sodium chloride (NaCl)

15. Hydrogen Bonds are weak bonds important in the chemistry of life
Attractive force between electropositive hydrogen of one molecule and an electronegative atom of another molecule

16. + –
Hydrogen bond + + – – – + + + –
(a) The slightly positive ends (+) of the water molecules become aligned with the slightly negative ends (–) of other water molecules.

17. Properties of Water Charged Exists as Gas, Liquid and Solid
Good solvent
Adhesion and Cohesion (via H-bonds)
Surface tension
Ionizes into acid and base

18. Properties of Water Cohesion Adhesion Water binding to water
Water binding to anything that has a charge
Remember water has a charge and thus will bind to anything with a charge

19. Capillary Action