1. Life’s Chemical Basis
Chapter 2

2. Building Block of Matter
Atoms: Tiny, indivisible particles, the building blocks of matter
Made up of
neutrons (n0) in the nucleus
protons (p+) in the nucleus
electrons (e-) orbiting around the nucleus
A typical atom has the same number of protons and electrons
Atomic Number: number of protons found in nucleus of the atom – IT NEVER CHANGES

3. Building Blocks of Matter
Element: pure substance that consists only of atoms with the same number of protons
Periodic Table: tabular arrangement of all known elements by their atomic number

4. Building Blocks of Matter
Although all atoms of an element have the same number of protons, they can differ in the number of other subatomic particles
Isotopes: forms of an element that differ in the number of neutrons their atoms carry
Mass Number: total number of protons and neutrons in the atomic nucleus
Radioisotope: isotope with an unstable nucleus

5. Building Blocks of Matter
Ion: an atom that has gained/lost electrons in order to achieve a full valence shell, ions carry a charge
If it gives up an electron, it becomes positively charged
If it gains an electron, it becomes more negative

6. Building Blocks of Matter
Chemical Bond: attractive force that arises between two atoms when their electrons interact
Compound: a pure substance formed when two or more different elements combine
Each has a chemical formula (H2O) and formed by a specific combination of elements in a fixed ratio

7. Building Blocks of Matter
Ionic bond: an electrical attraction between two oppositely charged atoms or groups of atoms
Ions retain their respective charges when in an ionic bond, therefore, one end of the ionic bond has a positive charge, and the other has a negative charge

8. Building Blocks of Matter
Polarity: separation of charge into positive and negative regions
Electronegativity: an atom’s ability to pull electrons away from other atoms

9. Building Blocks of Matter
Covalent Bond: forms when a pair of electrons is shared
Formed between atoms with a small or no difference in electronegativity
Covalent bonds are often stronger than ionic bonds, but not always

10. Building Blocks of Matter
Covalent bonds in compounds are usually polar
When atoms share electrons unequally in covalent bond, they are called polar covalent
Example: water molecules
Atoms that share electrons equally are nonpolar covalent

11. Water
H2O has unique properties that arise from the two polar covalent bonds in each molecule
The oxygen atom carries a slight negative charge; the hydrogen atoms carry a slight positive charge
The polarity of individual H2O molecules attracts them to one another in a hydrogen bond
Hydrogen bond: attraction between a covalently bonded hydrogen atom and another atom taking part in a separate polar covalent bond

12. Water
Hydrogen bonds form and break more easily than covalent or ionic bonds, BUT collectively are quite strong
Hydrogen bonds stabilize DNA and protein structures
Extensive hydrogen bonding among H2O molecules gives liquid H2O several special properties that make life possible

13. Water 1. Water is a Universal Solvent
Solvent: substance in which another is dissolved
Solute: the substance that is dissolved
Substances that dissolve easily in water are hydrophilic (water loving)
Ionic solids, such as sodium chloride (NaCl), and nonionic solids (e.g., sugars) dissolve in water
Substances that resist dissolving in water are hydrophobic (e.g., oils)

14. Water 2. Water has Cohesion
Cohesion: tendency of molecules to resist separating from one another
Water has cohesion because hydrogen bonds collectively exert a continuous pull on its individual molecules
REQUIRES ENERGY
The strong attraction to other water creates high surface tension.
This causes droplets to form.

15. Water 3. Water has Adhesion
Adhesion: force of attraction between unlike molecules
It forms hydrogen bonds with other molecules on other surfaces (think of tape)
This causes capillary action (water travelling up the stems of a plant)

16. Water 4. Water Stabilizes Temperature
Because of hydrogen bonding, it takes more heat to raise the temperature of water compared with other liquids
Below 0°C (32°F), water molecules become locked in the bonding pattern of ice
Sheets of ice that form on the surface of ponds, lakes, and streams insulate the water
Protects aquatic organisms during cold winters

17. Acids & Bases
Remember, water is a universal solvent because of its polarity
Your body is about 70% water
When water is liquid, some of its molecules spontaneously separate into hydrogen ions (H+) and hydroxide ions (OH–)

18. Acids & Bases
Acid: Substance that releases hydrogen ions (H+) when dissolved in water
The more hydrogen released, the more acidic the solution becomes
Base: Substance that releases hydroxide ions (OH-) when dissolved in water
The more hydroxide released, the more basic the solution becomes

19. pH Scale pH: measure of hydrogen ions in a solution
Bases accept hydrogen ions in water, pH > 7
Acids release hydrogen ions in water, pH < 7
The closer a substance is to 7, the weaker it is

20. Acids & Bases Acids and bases are key substances in biology.
Most biological molecules can function properly only within a narrow range of pH – HOMEOSTASIS!
Buffers: mixtures that can react with acids or bases to keep the pH within a particular range.
Antacids, blood

21. Acids & Bases
The fluids inside cells stay within a consistent range of pH because they are buffered
Buffer failure can be catastrophic in a biological system
Burning fossil fuels such as coal releases sulfur and nitrogen compounds that affect the pH of rain

22. Mercury Rising
Mercury is a naturally occurring element, mostly safely locked away in rocks
Volcanic and human activity release it into the atmosphere and it combines with carbon to form methylmercury
This easily crosses skin and mucous membranes, causing damage to the nervous system, brain, kidneys, and other organs

23. Mercury Rising
The toxin can build up to high levels if even small amounts are ingested on a regular basis, and can take months or years to be cleared from the body
Large predatory fish have a lot of mercury
U.S. Environmental Protection Agency recommends that adult humans ingest less than 0.1 microgram of mercury per kilogram of body weight per day