Lab 1: Measurements & Chemistry – Foundations for Biology

Measurements & Conversions

Metric and Imperial Systems

The metric system is the standard for scientific measurement due to its simplicity and universal use. It is based on powers of ten, making conversions straightforward. The imperial (English) system, commonly used in the United States, relies on less consistent conversion factors.

• Metric base units: meter (length), gram (mass), liter (volume), degree Celsius (temperature).

• Prefixes: Indicate powers of ten (e.g., kilo- = 103, centi- = 10-2).

• Scientific notation: Compact way to express large or small numbers, e.g., $6.5 \times 10^6$.

Example: 1 kilometer = 1,000 meters; 1 liter = 1,000 milliliters.

Prefix	Symbol	Exponential Notation	Value
kilo	k	$10^3$	1,000
centi	c	$10^{-2}$	0.01
milli	m	$10^{-3}$	0.001
micro	μ	$10^{-6}$	0.000001

Conversions between metric and imperial units are essential for laboratory work.

Measurement Practice

Accurate measurement of length, mass, and volume is foundational in biology labs. Common tools include rulers, measuring tapes, and balances.

• Length: Measured in meters (m), centimeters (cm), millimeters (mm).

• Mass: Measured in grams (g), milligrams (mg), ounces (oz).

• Volume: Measured in liters (L), milliliters (mL), gallons (gal), fluid ounces (fl oz).

Example: Diameter of a penny: 2 cm = 20 mm = 20,000 μm. Circumference of biceps: 30 in = 76.2 cm. Mass of penny: 3.1 g = 3,100 mg = 0.109 oz. Bladder volume: 500 mL = 0.5 L = 0.132 gal = 16.907 fl oz.

Chemistry Fundamentals

Atomic Structure

Atoms are the basic units of matter, composed of subatomic particles: protons, neutrons, and electrons. The nucleus contains protons and neutrons, while electrons occupy shells around the nucleus.

• Atomic number: Number of protons; determines the element.

• Atomic mass: Sum of protons and neutrons.

• Electrons: Equal to protons in a neutral atom.

Example: Carbon (C): Atomic number 6, Atomic mass ≈ 12, Protons 6, Neutrons ≈ 6, Electrons 6.

Bohr Models & Electron Shells

Bohr models illustrate the arrangement of electrons in shells around the nucleus. The first shell holds up to 2 electrons; subsequent shells hold up to 8 electrons. The outermost shell is the valence shell, which determines chemical reactivity.

• Octet rule: Atoms are most stable with 8 electrons in their valence shell (except H and He).

• Valence electrons: Electrons in the outermost shell; involved in bonding.

Example: Magnesium (Mg) has 12 electrons: 2 in the first shell, 8 in the second, 2 in the third.

Chemical Bonding

Chemical bonds form when atoms interact to achieve full valence shells. The main types are ionic and covalent bonds.

• Ionic bonds: Formed by transfer of electrons between atoms with large electronegativity differences, resulting in charged ions (e.g., NaCl).

• Covalent bonds: Formed by sharing electrons between atoms. If electrons are shared unequally, the bond is polar covalent; if shared equally, it is nonpolar covalent.

Bond Type	Electron Movement	Resulting Particles
Ionic	Transfer	Positive and negative ions
Covalent (polar)	Unequal sharing	Partial charges
Covalent (nonpolar)	Equal sharing	No charge separation

Example: Water (H2O) forms polar covalent bonds; sodium chloride (NaCl) forms ionic bonds.

Hydrophilic vs. Hydrophobic Compounds

Hydrophilic substances are "water-loving" and dissolve in water due to polar bonds. Hydrophobic substances are "water-fearing" and do not dissolve in water, typically containing nonpolar bonds.

• Polar molecules: Dissolve in water (hydrophilic).

• Nonpolar molecules: Do not dissolve in water (hydrophobic).

Example: Oil is hydrophobic (nonpolar), water is hydrophilic (polar), so they do not mix.

Acids, Bases, and Buffers

Acids release hydrogen ions (H+), while bases accept hydrogen ions or release hydroxide ions (OH-). The pH scale (0–14) measures acidity or basicity; lower pH is acidic, higher pH is basic.

• Acidic: pH < 7

• Neutral: pH = 7

• Basic: pH > 7

Fluid	Normal pH Range	Classification
Saliva	6.7–7.6	Acidic
Blood	7.35–7.45	Neutral
Urine	5–8	Acidic
Gastric juice	1.5–3.5	Acidic

Buffers stabilize pH by neutralizing added acids or bases. In biological systems, buffers are vital for maintaining homeostasis, such as the bicarbonate buffer system in blood.

• Example: When acid is added to water, pH drops sharply. When acid is added to a buffer, pH changes minimally.

Summary Table: Key Concepts

Concept	Definition	Example/Application
Metric System	Measurement system based on powers of ten	1 km = 1,000 m
Atomic Number	Number of protons in an atom	Carbon: 6
Ionic Bond	Electron transfer between atoms	NaCl
Covalent Bond	Electron sharing between atoms	H2O
Buffer	Substance that stabilizes pH	Bicarbonate in blood