1. CHAPTER 2
The Chemistry of Life

2. Atoms, Ions and Molecules
Concept 2.1
Atoms, Ions and Molecules

3. ELEMENTS Element: pure substance
Cannot be broken down into other substances by chemical means
25 elements are essential to life

4. ELEMENTS 4 elements make up 96% of all living matter Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Carbon (C)

5. ELEMENTS
Calcium (Ca), phosphorus (P), potassium (K), sulfur (S)  most of remaining 4%
Trace elements:
less than 0.01 % of body mass
are essential to life
E.g.: iodine (I), copper (Cu), fluorine (F), manganese (Mn), and selenium (Se)

6. Iodine is a trace element that prevents goiter

7. COMPOUNDS
COMPOUNDS: substance containing two or more elements combined in a fixed ratio
Compound properties may differ greatly from the elements they contain
H2O – liquid at room temperature, while hydrogen and oxygen are both gases
NaCl – white crystal (table salt), while sodium is a silver-gray metal and chlorine is a yellowish-green gas

8. Na+ + Cl-  NaCl

9. ATOMS Atom: smallest possible particle of an element
Made up of 3 subatomic particles:
proton: single unit of (+) charge
electron: single unit of (-) charge
neutron: electrically neutral—no charge

10. ATOMIC NUCLEUS Forms central core of atom
Made up of tightly packed protons and neutrons
Nucleus has a net (+) charge due to the protons it contains

11. ATOMIC NUMBER
All the atoms of a particular element have the same number of protons
Atomic number: the number of protons in the nucleus of an element
Examples:
Carbon has 6 protons  atomic number is 6
Helium has atomic number of 2  helium has 2 protons

12. ELECTRONS
Small negatively charged particles that travel around nucleus
Pictured as traveling around nucleus in a “cloud”

13. ELECTRONS & REACTIVITY
Electrons are said to belong to different energy levels
First or lowest level contains 2 electrons and is closest to nucleus
Each of the other energy levels contains 8 electrons.

14. ELECTRON ENERGY LEVELS
If the outer most shell is not filled, the atom is reactive.
The electrons in the outermost shell are called valence electrons.

15. Valence Electrons (Bohr Model)

17. Valence Electrons (Lewis Structure)

18. CHEMICAL BONDS JOIN ATOMS TO ONE ANOTHER
Concept 4.3
CHEMICAL BONDS JOIN ATOMS TO ONE ANOTHER

19. CHEMICAL BONDS
Atoms react with one another to fill their outer energy levels
One atom may transfer an electron to another atom or two atoms may share electrons
Transferring or sharing electrons creates an attraction called a chemical bond that holds atoms together

20. IONIC BONDS Ionic bond: one atom transfers an electron to another atom
Ions: atoms that become electrically charged as a result of gaining or losing an electron
Oppositely charged ions are attracted to one another forming a chemical bond  an ionic bond

22. COVALENT BONDS Formed when atoms share electrons
Electrons may be shared equally or unequally
Molecule: two or more atoms held together by covalent bonds

24. CHEMICAL REACTIONS
Breaking of old chemical bonds and formation of new chemical bonds resulting in the formation of new substances
Reactants: starting material for a chemical reaction
Products: material created as a result of a chemical reaction

25. CHEMICAL EQUATION

26. LIFE DEPENDS ON THE UNIQUE PROPERTIES OF WATER
Concept 4.4
LIFE DEPENDS ON THE UNIQUE PROPERTIES OF WATER

27. WATER MOLECULE Water is a polar molecule
Electrons in bond are not shared equally between hydrogen and oxygen
Electrons attracted to oxygen more strongly than to hydrogen
Results in an internal separation of charge
Note: Hydrogen atoms in the water molecule are slightly positive and the oxygen atom slightly negative

28. POLARITY & HYDROGEN BONDING

29. WATER’S LIFE-SUPPORTING PROPERTIES
Polarity of water and effects of hydrogen bonding give water with unique properties:
Cohesion and adhesion
Temperature moderation
Low density of ice compared to water
Ability to dissolve substances

30. COHESION & ADHESION Cohesion: an attraction between like molecules
Water’s polarity results in hydrogen bonds forming between water molecules
Adhesion: an attraction between unlike molecules
Both cohesion and adhesion are important forces in the living world

31. COHESION & ADHESION
Keep large molecules organized so they function properly in cells
Help transport water through roots and leaves in plants
Provides surface tension on surfaces of ponds and lakes

32. TEMPERATURE MODERATION
Hydrogen bonds in water molecules allow water temperatures to change more slowly
Causes oceans and lakes to moderate temperatures of nearby land areas  less extreme temperatures in coastal areas
Through evaporation (sweating), water moderates temperature  absorbs heat energy from skin cooling the body

33. LOW DENSITY OF ICE Density: amount of matter/given volume
For most substances, solids are more dense than liquid state of matter
Due to hydrogen bonding, water is the opposite
Liquid water more dense than solid water
Since less dense substances float in more dense substances, ice floats

34. LOW DENSITY OF ICE Why is this important to living things?
If ice sank, bodies of water would freeze from the bottom up
Organisms could NOT get to nutrients on the bottom and would be trapped
Ice insulates the water below, allowing life to persist below the frozen surface

35. WATER DISSOLVES OTHER SUBSTANCES
Solution: uniform mixture of two or more substances
Solvent: the substance that dissolves the other substance; present in the greater amount
Solute: the substance that is dissolved; present in the lesser amount
Aqueous solution: solution where water is the solvent

36. SOLUTIONS

37. ACIDS, BASES, & pH
Acid: a compound that donates H+ ions to aqueous solutions
Base: a compound that removes H+ ions from an aqueous solution
pH scale: range of numbers that describes how acidic or how basic a solution is
pH scale ranges from 0 (most acidic) to 14 (most basic); pH of 7 is neutral

38. ACIDS, BASES, & pH

39. BUFFERS
Buffers: substances that cause a solution to resist changes in pH
Molecules in cells are very sensitive to even small changes in pH
Many biological fluids such as blood contain buffers that maintain its pH at or very near 7.4

40. THE END

41. BUFFERS

42. COVALENT BONDS

44. STABLE ISOTOPES
Most isotopes are stable—their nuclei do not change over time
Other isotopes contain nuclei that will change or decay over time