1. The Chemical Basis of Life
Chapter 4
The Chemical Basis of Life

2. Matter
Matter = any material substance with Mass & Volume

3. Matter
comes in 3 phases
Liquid
Solid
Gas

4. Solid
Definite Shape
Definite Volume

5. Liquid Indefinite Shape – takes the shape of the container
Definite Volume

6. Gas Indefinite Shape – takes the shape of the container
Indefinite Volume – can expand and be compressed

7. Elements
Pure substance that can not be broken down into other substances by chemical means

8. Examples of Elements C = Carbon Na = Sodium O = Oxygen Ca = Calcium K
= Potassium H
= Hydrogen I
= Iodine N
= Nitrogen Cl
= Chlorine S
= Sulfur P
= Phosphorus

9. 4 elements make up 96% of all living matter
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Carbon (C)

10. Most of remaining 4% is made of:
Calcium (Ca),
phosphorus (P),
potassium (K),
sulfur (S)
Trace elements Make up less than 0.01 % of body mass
Essential to life

11. Atom
the smallest particle making up elements

12. Sub-atomic Particles Protons p+ - positive charge, in nucleus
Neutrons n0 – no charge, in nucleus
Electrons - e- negative charge, orbiting nucleus

13. C Carbon Atom 6 12.011 Atomic # = # of p+ and # of e-
Carbon has 6 p+ and 6 e-
Atomic Mass
minus Atomic # = # of n0
Carbon has 6 n0

14. Drawing an Atom of Carbone- e-
6 p+
6 n0

15. HELIUM ATOM + - + - Shell proton neutron electron
What do these particles consist of?

16. Compounds
Substance containing two or more elements combined in a fixed ratio
Properties are usually much different than those of the elements they contain
Ex: H2O – liquid at room temperature, while hydrogen and oxygen are both gases
Ex: NaCl – white crystal (table salt), while sodium is a silver-gray metal and chlorine is a yellowish-green gas

17. Isotopes
Atoms with the same number of protons, but different numbers of neutrons.
Atoms of the same element (same atomic number) with different mass numbers
Most isotopes are stable—their nuclei do not change over time

18. Radioactive Isotope
Other isotopes contain nuclei that will change or decay over time
Unstable isotopes
Nucleus changes giving off radiation
May be harmful
Can be useful in research and/or medical diagnosis and treatment

19. Let’s practice What We Just Learned

20. Bohr Diagram and Lewis Structure

21. Bigger energy level = higher energy
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells around the nucleus of an atom.
first shell a maximum of 2 electrons
second shell a maximum of 8 electrons
third shell a maximum of 8 electrons
Bigger energy level = higher energy

22. ATOMIC STRUCTURE: Bohr Diagram
With the Bohr Diagram (Dot & Cross diagrams) elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X
Nitrogen N 7 X X
7P+
7n0 X X 14 X X

23. Bohr Diagrams O Cl Draw the Bohr Diagram for the following elements: X8 17 O Cl a) b) 35 X X 16 X X X X X
17p+
18n0 X X X X X X
8p+
8n0 X X X X X X X X X X

24. Bohr Diagrams B Ne Draw the Bohr Diagram for the following elements: X5 10 B Ne c) d) 20 X X 11 X X X X
10p+
10n0 X X X X X X
5p+
6n0 X X X

25. Valence Electrons The electrons on the outermost energy level
These electrons determine the element’s chemical properties and its ability to form chemical bonds.

26. Lewis Structure of Atom
The chemical symbol for the atom is surrounded by a number of dots corresponding to the number of valence electrons.
Examples
Hydrogen atom has 1 valence electron H
Fluorine atom has 7 valence electrons F

27. Lewis Structure Draw the Lewis Structure for the following elements:
a) Li b) Cl
c) P d) Mg

28. Let’s practice What We Just Learned

29. Chemical Bonding
Ionic and Covalent

30. Chemical Bonds
Atoms react with one another to fill their outer energy levels
Transferring or sharing electrons creates an attraction (chemical bond) that holds atoms together

31. Noble Gases
Helium, neon and argon are atoms which do not react with other atoms.
We call them “Noble Gases” because of this.
Each of these gases has a full outer electron shell.
10p10n
18p22n
2p2n 2 Ne 10 He 20 4 Ar 18 40
2,8
2,8,8

32. IONIC BONDS Ionic bond: one atom transfers an electron to another atom
Oppositely charged ions are attracted to one another forming a chemical bond  an ionic bond

33. Sodium 11 Na 23
e.c. 2,8,1
11p
12n
11 protons
12 neutrons
11 electrons

34. Chlorine Cl e.c. 2,8,7 17 protons 18 Neutrons 17 electrons 17 35 17p

35. + The Sodium atom has 1 Electron in it’s outer shell.Na
e.c. 2,8,1
Atom +
The Sodium loses 1 electron to leave a complete outer shell.
It is now a Sodium ion with a charge of 1 +
(Na +)
e.c. (2,8)+
Ion

36. - The Chlorine atom has 7 electrons in it’s outer shell.Cl
e.c. 2,8,7
Atom -
(Cl - )
The Chlorine gains 1 electron to gain a complete outer shell.
It is now a Chlorine ion with a charge of 1 -
e.c. (2,8,8)-
Ion

37. The Ionic Bond + - Sodium atom Na Chlorine atom Cl Sodium ion (Na +)
Chlorine ion
(Cl -)
The sodium atom loses one electron to attain a complete outer shell and become a positive ion (Na +).
The Chlorine atom gains one electron to attain a complete outer shell and become a negative ion (Cl –).
Strong forces attract the sodium and chlorine ions.

38. Covalent Bond Formed when atoms share electrons
Electrons may be shared equally or unequally
Molecule: two or more atoms held together by covalent bonds

39. Chlorine atom 2,8,7

40. 2 Chlorine atoms
Outer shells only

41. Chlorine molecule Cl2
Electrons shared
Each outer shell has 8 electrons
Forces (bonds) between atoms in the molecule are very strong
Molecules have no overall electric charge

42. Covalent bonds can be represented in 3 ways:
Chlorine Cl2 Cl Cl Cl Cl

43. Oxygen O 16 8
Oxygen atom 2,6

44. 2 Oxygen atoms (outer shells only)
Double covalent bond O

45. Let’s practice What We Just Learned

46. LIFE DEPENDS ON THE UNIQUE PROPERTIES OF WATER

47. Water Molecule Water is a polar molecule
Electrons are not shared equally between hydrogen and oxygen
Electrons attracted to oxygen more strongly than to hydrogen
Note: Hydrogen atoms in the water molecule are slightly positive and the oxygen atom slightly negative

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

49. COHESION & ADHESION Cohesion: an attraction between like molecules
Adhesion: an attraction between unlike molecules
Keep large molecules organized so they function properly in cells
Help transport water through roots and leaves in plants

50. TEMPERATURE MODERATION
Hydrogen bonds in water molecules allow water temperatures to change more slowly
Through evaporation (sweating), water moderates temperature  absorbs heat energy from skin cooling the body

51. 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 is more dense than solid water
Since less dense substances float in more dense substances, ice floats

52. 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

53. ACIDS, BASES, & pH Acid: Base:
produce H+ ions in water
pH less than 7
sour taste
Base:
removes H+ ions in water
pH greater than 7
bitter taste
pH scale: range of numbers that describes how acidic or how basic a solution is
pH of 7 is neutral
Buffers: substances that cause a solution to resist changes in pH