1. Basic Chemistry
Ch. 2

2. Organisms are Composed of Elements
Elements cannot be broken down by ordinary chemical means
Elements are composed of atoms or unique building blocks for each element
Compounds
Substances consisting of two or more different elements combined in a fixed ratio
(C6H12O6 and NaCl)
Molecules
Substances consisting of two or more elements; elements can be the same or different

3. Atoms and Atomic Structure
Three important subatomic particles exist:
Neutrons
No charge in the nucleus, 1 atomic mass unit (amu)
Protons
Positive charge, in the nucleus, 1 amu
Electrons
Negative charge, orbit nucleus, 0 amu
Equal to the number of protons in an atom
Atoms of different elements contain different numbers of subatomic particles
Compare hydrogen, helium and lithium

4. Atoms Have a Unique Number of Protons
Neutron
Electron
Hydrogen (H)
Helium (He)
Lithium (Li)
Figure 2.2

5. Identifying Atoms Using Atomic Number and Atomic Mass
Atomic number = number of protons in nucleus
Mass number = mass of protons and neutrons in the atoms nucleus
Atoms of the same element can have different mass numbers
Isotopes are atoms of the same element that differ in their number of neutrons

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

7. Radioactive Isotopes Can Help or Harm Us

8. 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 (unreactive) elements have a full valence shell
Unstable (reactive) elements lack a full valence shell and will gain, lose, or share electrons with other atoms to achieve stability, & thereby forming bonds

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

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

11. Covalent Bonds Join Atoms Into Molecules Through Electron Sharing
Electrons are shared
Allows each atom to fill its valence shell part of the time
Sharing may be equal or unequal
Equal sharing produces nonpolar molecules (Ex. 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

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

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

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

15. 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)

16. Hydrogen Bonds +
An electrostatic attraction between a positive hydrogen and an electronegative atom –
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 Exists as Solid, Liquid, Gas
Charged
Ionizes into an acid and base
Exists as Solid, Liquid, Gas
Adhesion and Cohesion (via H-bonds)
Surface tension
Great solvent

18. Properties of Water Cohesion Adhesion Water binding to water
Water binding to anything that has a charge

19. Capillary Action