1. Matter, Chemical Bonds, Chemical Reactions

2. The World of Elements

3. About 25 elements are essential for life
Four elements make up 96% of living matter:
• carbon (C) • hydrogen (H)
• oxygen (O) • nitrogen (N)
Also important to the structure of living things are phosphorus (P) and sulfur (S)

4. Parts of an Atom What’s an atom?
the smallest part of an element that still retains all of the properties of that element
Parts of an Atom
Nucleus (core) – contains:
Protons (positively charged particles)
Number of protons = atomic number on periodic table
Neutrons (uncharged, neutral particles)
Electrons (negatively charged)
orbit the nucleus (in the electron cloud)
Number of protons=number of electrons (in a neutral atom) = atomic number

5. Isotopes - have the same numbers of protons and electrons but different numbers of neutrons
Because the number of electrons in isotopes do not change, all isotopes of an element have the same chemical properties and living cells cannot distinguish between them

6. Chemical behavior of an atom depends on its electron arrangement
Specifically, behavior is determined by the number of electrons in its outermost shell, the valence shell
Atoms are seeking stability and find it by forming chemical bonds with other atoms (by gaining, losing or sharing electrons)

7. Ionic bonds
Transfer of electrons; one atom gains an electron(s) while the other loses an electron(s)
Forms + & - ions
A charged particle that has either a negative or positive charge (EX: Na+ or Cl-)
Opposites attract

8. Covalent bonds Result from the sharing of electrons
Strong bond- both atoms holding onto the electrons
May be nonpolar (equal pull on electrons) or polar (unequal sharing of electrons which creates a slightly positive and a slightly negative end)

9. Chemicals that contribute H+ to a solution
Acids
Chemicals that contribute H+ to a solution
An example is hydrochloric acid (HCl)
This is the acid in your stomach that aids in digestion
More H+ ions in solution (and fewer OH- ions)
Bases (alkaline)
Chemicals that remove hydrogen ions from solution
Ex: sodium hydroxide (NaOH)
More OH- ions in solution (and fewer H+ ions)
Teaching Tips
1. Discussions of pH are enhanced by lab activities that permit students to test the pH of everyday items (foods and household solutions). If students do not have opportunities to conduct such tests in labs, consider testing a few items during your class (pH paper or a basic pH meter will, of course, be necessary).
Copyright © 2009 Pearson Education, Inc.

10. Acidic solution Basic solution Neutral solution
Figure 2.15 The pH scale represents the relative concentration of H+ and OH–.
Acidic solution
Neutral solution
Basic solution

11. pH and the pH Scale Solutions that are acidic have a lower pH
Solutions that are basic have a higher pH
The pH scale runs from 0-14
7 is neutral
less than 7 is acidic,
more than 7 is basic
Examples of acids: vinegar, soft drinks, lemon juice, coffee, hydrochloric acid
Examples of bases: bleach, ammonia, sodium hydroxide

12. (Higher concentration of H+) (Lower concentration of H+)
pH scale 1
Battery acid 2
Lemon juice, gastric juice 3
Grapefruit juice, soft drink,
vinegar, beer
(Higher concentration of H+)
Increasingly ACIDIC
Acidic solution 4
Tomato juice 5
Rain water 6
Human urine
Saliva
NEUTRAL
[H+]=OH–] 7
Pure water
Human blood,
tears 8
Seawater
Neutral solution 9
Figure 2.15 The pH scale represents the relative concentration of H+ and OH–. 10
(Lower concentration of H+)
Increasingly BASIC
Milk of magnesia 11
Household ammonia 12
Household bleach 13
Oven cleaner
Basic solution 14

13. pH of Organisms Most biological fluids have pH 6 – 8
pH values in human stomach can reach 2
Internal pH of living things must remain fairly stable so that chemical reactions can occur optimally (homeostasis)