1. Life and Chemistry: Small Molecules

2. Life and Chemistry: Small Molecules
Water and the Origin of Life’s Chemistry
Atoms: The Constituents of Matter
Chemical Bonds: Linking Atoms Together
Chemical Reactions: Atoms Change Partners
Water: Structure and Properties
Acids, Bases, and the pH Scale
Properties of Molecules

3. Water and the Origin of Life’s Chemistry
The earliest chemical signatures of life on Earth are about 4 billion years old.
The presence of water, possibly brought by comets striking the Earth, was critical in making conditions suitable for life.
Environmental conditions conducive to life evolved during the Hadean period.

4. Atoms: The Constituents of Matter
All matter is composed of atoms.
Each atom consists of at least one proton and one electron.
Atoms have mass. The mass comes mostly from the proton and a neutrally charged body called a neutron.

5. Figure 2.2 The Helium Atom

6. Atoms: The Constituents of Matter
Each element contains only one type of atom.
Information on elements is arranged in logical order in a table called the periodic table.
The periodic table arranges elements left to right based on their atomic number, and in columns based on similarities in their properties.

7. Figure 2.3 The Periodic Table (Part 1)

8. Figure 2.3 The Periodic Table (Part 2)

9. Atoms: The Constituents of Matter
The region in which an electron travels is called the electron’s orbital.
The orbitals constitute a series of electron shells, or energy levels, around the nucleus.
Two electrons at most can occupy each orbital.

10. Atoms: The Constituents of Matter
The tendency of atoms to be stable when they have eight electrons in their outermost shells is called the rule of eight, or the octet rule.
Hydrogen and phosphorus are exceptions to the octet rule.

11. Life and Chemistry: Small Molecules
Water and the Origin of Life’s Chemistry
Atoms: The Constituents of Matter
Chemical Bonds: Linking Atoms Together
Chemical Reactions: Atoms Change Partners
Water: Structure and Properties
Acids, Bases, and the pH Scale
Properties of Molecules

12. Chemical Bonds: Linking Atoms Together
A molecule is two or more atoms bonded together.
A chemical bond is an attractive force that links two atoms together.

13. Chemical Bonds: Linking Atoms Together
A covalent bond is formed by sharing of a pair of electrons between two atoms.
In hydrogen molecules (H2), a pair of electrons share a common orbital and spend equal amounts of time around each of the two nuclei.
The nuclei stay some distance from each other due to mutually repelling positive charges.

14. Properties of Molecules
Figure The Polar Covalent Bond in the Water Molecule
Properties of Molecules

15. Chemical Bonds: Linking Atoms Together
Hydrogen bonds may form within or between atoms with polar covalent bonds.
The d– portion of one molecule has a weak attraction to the d+ portion of another molecule. Each of these attractions is called a hydrogen bond.
Hydrogen bonds do not share electrons.
Although hydrogen bonds are weak, they tend to be additive, and they are of profound biological importance.

16. Properties of Molecules
Figure Hydrogen Bonds Can Form between or within Molecules
Properties of Molecules

17. Chemical Bonds: Linking Atoms Together
Ionic bonds involve a complete transfer of one or more electrons, or are formed by the electrical attraction between ions with opposite charges.
Ions are formed when an atom loses or gains electrons.
Table salt has chloride and sodium ions, held together by ionic bonds.
When salt is introduced into water, the partial charges of the water molecules can easily interfere with the ionic bonds.

18. Properties of Molecules
Figure Water Molecules Surround Ions
Properties of Molecules

19. Chemical Bonds: Linking Atoms Together
Polar molecules tend to be hydrophilic.
Nonpolar molecules are called hydrophobic because they tend to aggregate with other nonpolar molecules.

20. Water: Structure and Properties
PROPERTIES OF WATER
High Specific heat
Cohesion
Adhesion
Less dense as a solid than a liquid
Universal solvent

21. Properties of Molecules
Figure Hydrogen Bonds Hold Water Molecules Together (Part 1)
Properties of Molecules

22. Water: Structure and Properties
Living organisms are over 70 percent water by weight and many reactions take place in this watery environment.

23. Acids, Bases, and the pH Scale
Some substances dissolve in water and release or DONATE hydrogen ions (H+) … acids.
Other substances dissolve in water and release or DONATE hydroxide ions (OH–) …bases.

24. Acids, Bases, and the pH Scale
pH is the measure of hydrogen ion concentration.
THINK PERCENT HYDROGEN

25. Properties of Molecules
Figure pH Values of Some Familiar Substances
Properties of Molecules

26. Properties of Molecules
Figure Buffers Minimize Changes in pH
Properties of Molecules

27. Properties of Molecules
Functional groups give specific properties to molecules.
Functional groups are covalently bonded to organic molecules.
Amino acids are biological molecules that contain both a carboxyl group and an amino group.

28. Properties of Molecules
Figure Some Functional Groups Important to Living Systems (Part 1)
Properties of Molecules

29. Properties of Molecules
Figure Some Functional Groups Important to Living Systems (Part 2)
Properties of Molecules

30. Properties of Molecules
Figure Some Functional Groups Important to Living Systems (Part 3)
Properties of Molecules