Introductory Chemistry Study Notes: Units, Measurements, and Fundamental Constants

Units and Measurements in Chemistry

SI Units and Physical Quantities

The International System of Units (SI) is the standard for scientific measurements, providing consistency and clarity in chemistry. Each physical quantity has a specific SI unit and abbreviation.

• Length: meter (m)

• Mass: kilogram (kg)

• Time: second (s)

• Temperature: kelvin (K)

• Amount of substance: mole (mol)

• Volume: cubic meter (m3)

• Pressure: pascal (Pa)

• Energy: joule (J)

• Electrical charge: coulomb (C)

Greek Prefixes and Their Meanings

Prefixes are used to denote multiples or fractions of units, making it easier to express very large or very small quantities.

• Giga- (G): one billion ($10^9$)

• Mega- (M): one million ($10^6$)

• Kilo- (k): one thousand ($10^3$)

• Deci- (d): one-tenth ($0.1$ or $10^{-1}$)

• Cent- (c): one-hundredth ($0.01$ or $10^{-2}$)

• Milli- (m): one-thousandth ($0.001$ or $10^{-3}$)

• Micro- (\mu): one-millionth ($10^{-6}$)

• Nano- (n): one-billionth ($10^{-9}$)

• Pico- (p): one-trillionth ($10^{-12}$)

Conversion Table for Metric Prefixes

This table helps convert between different metric prefixes by moving the decimal point left (L) or right (R) as indicated.

Useful Conversion Factors

Length

Length is measured in meters (m), but other units are commonly used. Conversion factors allow for easy switching between units.

• 1 km = 0.62137 mi

• 1 m = 39.37 in

• 1 m = 1.0936 yd

• 1 in = 2.54 cm (exactly)

• 1 cm = 0.39370 in

• 1 Å = $10^{-10}$ m

• 1 nm = $10^{-9}$ m

Mass/Weight

Mass is measured in kilograms (kg) in the SI system. Other units include grams (g), pounds (lb), and atomic mass units (amu).

• 1 kg = $10^3$ g = 2.2046 lb

• 1 lb = 16 oz = 453.6 g

• 1 ton = 2000 lb

• 1 atomic mass unit = $1.66 \times 10^{-24}$ g

Volume

Volume is measured in cubic meters (m3) in SI, but liters (L) and milliliters (mL) are also common in chemistry.

• 1 L = $10^{-3}$ m3 = 1 dm3 = $10^3$ cm3 = 1.057 qt

• 1 L = 0.264 gal

• 1 m3 = 264 gal

• 1 gal = 4 qt = 3.7854 L

• 1 cm3 = 1 mL

• 1 in3 = 16.4 cm3

Temperature

Temperature is measured in kelvin (K) in SI. Conversion between Celsius, Fahrenheit, and Kelvin is often required.

• 0 K = -273.15°C = -459.67°F

• K = °C + 273.15

• °C = $\frac{5}{9}(°F - 32)$

• °F = $\frac{9}{5}(°C) + 32$

Energy

Energy is measured in joules (J) in SI. Other units include calories (cal) and electron volts (eV).

• 1 J = 0.23901 cal

• 1 cal = 4.184 J

• 1 eV = $1.602 \times 10^{-19}$ J

• 1 J = 1 C × 1 V

Pressure

Pressure is measured in pascals (Pa) in SI. Other units include atmospheres (atm), millimeters of mercury (mm Hg), and pounds per square inch (psi).

• 1 Pa = 1 kg/(m·s2)

• 1 atm = 101,325 Pa

• 1 atm = 760 mm Hg (torr)

• 1 atm = 29.9 in Hg

• 1 atm = 14.696 lb/in2

Fundamental Constants in Chemistry

Important Constants

Fundamental constants are essential for calculations in chemistry, including atomic structure, stoichiometry, and thermodynamics.

• Avogadro's number: $6.022 \times 10^{23}$/mole

• Gas constant (R): $0.0821$ L·atm/(K·mol)

• Mass of electron (me): $9.109390 \times 10^{-31}$ kg

• Mass of neutron (mn): $1.674929 \times 10^{-27}$ kg

• Mass of proton (mp): $1.672623 \times 10^{-27}$ kg

• Planck's constant (h): $6.626 \times 10^{-34}$ J·s

• Speed of light (c): $3.00 \times 10^8$ m/s

The Periodic Table of Elements

Overview and Structure

The periodic table organizes all known elements by increasing atomic number and groups them by similar chemical properties. It is a foundational tool in chemistry for understanding element behavior, atomic structure, and chemical reactions.

• Groups: Vertical columns, elements share similar properties

• Periods: Horizontal rows, elements have increasing atomic number

• Element information: Symbol, atomic number, atomic weight

Element Symbols and Atomic Weights

Each element has a unique symbol and atomic weight, which are used in chemical equations and calculations.

Summary Table: SI Units and Physical Quantities

Physical Quantity	Name of Unit	Abbreviation
Length	meter	m
Mass	kilogram	kg
Time	second	s
Temperature	kelvin	K
Amount of substance	mole	mol
Volume	cubic meter	m3
Pressure	pascal	Pa
Energy	joule	J
Electrical charge	coulomb	C

Summary Table: Greek Prefixes

Greek Prefix	Meaning
giga- (G)	one billion ($10^9$)
mega- (M)	one million ($10^6$)
kilo- (k)	one thousand ($10^3$)
deci- (d)	one-tenth ($0.1$ or $10^{-1}$)
centi- (c)	one-hundredth ($0.01$ or $10^{-2}$)
milli- (m)	one-thousandth ($0.001$ or $10^{-3}$)
micro- (\mu)	one-millionth ($10^{-6}$)
nano- (n)	one-billionth ($10^{-9}$)
pico- (p)	one-trillionth ($10^{-12}$)

Summary Table: Fundamental Constants

Constant	Value
Avogadro's number	$6.022 \times 10^{23}$/mole
Gas constant (R)	$0.0821$ L·atm/(K·mol)
Mass of electron (me)	$9.109390 \times 10^{-31}$ kg
Mass of neutron (mn)	$1.674929 \times 10^{-27}$ kg
Mass of proton (mp)	$1.672623 \times 10^{-27}$ kg
Planck's constant (h)	$6.626 \times 10^{-34}$ J·s
Speed of light (c)	$3.00 \times 10^8$ m/s

Summary Table: Element Symbols and Atomic Weights

Refer to the provided table for a comprehensive list of element symbols and atomic weights, which are essential for stoichiometric calculations and understanding chemical reactions.