1. Essential Chemistry for Biology
Chapter 2

2. Why Chemistry??
Chemicals make up everything!
Body
Environment
Food

3. Basic Chemistry Matter Elements
Anything that takes up space and has mass
Can exist as a liquid, solid, or gas
Made up of atoms
Elements
Basic building block of matter
92 naturally occurring elements

4. Basic Chemistry
Only 6 elements that make up most of the body weight of organisms
C Carbon
H Hydrogen
N Nitrogen
O Oxygen
P Phosphorus
S Sulfur

5. Trace Elements
Trace elements make up 0.01% of human body weight, but still very important

6. Each Element Consists of ONE Kind of Atom
Smallest unit that retains the properties of a given element
And to enter a chemical reaction
Composed of subatomic particles:
Protons (p+)
Neutrons
Electrons (e-)
atomic nucleus
Usually (e-) = (p+)
Electrically neutral

7. Atomic Symbol Atomic Mass = Number of Protons + Number of Neutrons
Atomic Number = The Number of Protons
in the Nucleus

8. Why are electrons so important??
determine the chemical behavior of atoms
Part of atom that comes close enough for interactions
associated with energy
the field of energy around an atom is arranged as levels called electron shells

9. Electron Shells
have specific numbers of orbitals that may be filled with electrons
atoms that have incomplete electron orbitals tend to be more reactive
atoms will lose, gain, or share electrons in order to fill completely their outermost electron shell
these actions are the basis of chemical bonding

10. Valence Shell

11. Molecules and Compounds
Chemical bonding that joins atoms
Some contain atoms of only one element N2
Compounds
Atoms of two or more different elements
H2O
Mixture
Two or more molecules mingling together

12. Chemical Bonds Atoms are held together by bonds 3 main types:
Ionic bond
Accept or donate electrons
Covalent bond
Share one or more electrons
Hydrogen bond

13. Ionic Bond Atoms gain and lose electrons Ion Ionic bond
Balance between protons and electrons shifts
Become “ionized”
Ion
Atom that has a charge
Losing an electron results in a net positive
Gaining an electron results in a net negative charge
Ionic bond
Association of two ions that have opposing charges

14. Which will form an ionic bond?
Chlorine (Cl)
Argon (Ar)
Potassium (K)
Helium (He)

15. Can Mg and Cl form an ionic bond?
Magnesium (Mg)
Chlorine (Cl)

16. Covalent Bond Covalent bond Bond Notation
Stable and stronger than ionic bonds
Atoms share electrons
Each atom will have a completed outer shell
Bond Notation
Single covalent bonds are written as H-H
Double covalent bonds are written as O=O

17. A covalent bond can be nonpolar or polar
Nonpolar covalent bond
Sharing of electrons between atoms is fairly equal
Polar covalent bond
Unequal sharing of electrons

18. Hydrogen Bond Hydrogen bond Weak attraction
Form and break easily
Occurs between polar molecules
Polar bonds have charges on either end and often attract to each other

19. Water molecules contain two covalent bonds

20. Chemical Reactions
Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones
Reactants
Starting materials
Products
End materials
Chemical reactions cannot create or destroy matter,
They only rearrange it

22. Hydrogen Bonds Give Water Unique Properties
Heat Storage
water temperature changes slowly and holds temperature well
Ice Formation
few hydrogen bonds break at low temperatures
water becomes less dense as it freezes because hydrogen bonds stabilize and hold water molecules farther apart
High Heat of Vaporization
at high temperatures, hydrogen bonds can be broken
water requires tremendous energy to vaporize because of all the hydrogen bonds that must be broken

23. Hydrogen Bonds Give Water Unique Properties
Water molecules are sticky
cohesion – when one water molecule is attracted to another water molecule
adhesion – when polar molecules other than water stick to a water molecule

24. Hydrogen Bonds Give Water Unique Properties
Water dissolves other polar substances
Solvent
Ions and polar molecules easily dissolve in it
Solute
A dissolved substance
Hydrophilic
water-loving molecules
form hydrogen bonds with water
Hydrophobic
water-fearing molecules
do not form hydrogen bonds with water

25. Acids and Bases
When water ionizes, it releases an equal number of hydrogen ions (H+) and hydroxide ions (OH-)
Some substances release more or fewer or each
Acids - Excess hydrogen ions
Bases - Excess hydroxide ions

26. Acidic and Basic Solutions
Acidic Solutions
Sharp, sour taste
Molecules that dissociate in water
Release hydrogen ions (H+)
Basic Solutions
Bitter taste
Molecules that either take up hydrogen ions (H+) or release hydroxide ions (OH-)

27. pH Scale The pH Scale Buffer Ranges from 0 - 14
pH below 7 is acidic [H+] > [OH-]
pH above 7 is alkaline [OH-] > [H+]
pH of 7 is neutral [H+] = [OH-]
Buffer
Chemical or combination of chemicals that keeps pH within normal limits

28. pH = -log[H+] Water Ionizes
The amount of ionized hydrogen from water in a solution can be measured as pH
The pH scale is logarithmic, which means that a pH scale difference of 1 unit actually represents a 10-fold change in hydrogen ion concentration
pH = -log[H+]

29. The pH scale