General Chemistry Basics: Matter, Measurement, and Radioactivity

Chapter 1: Chemistry Basics—Matter and Measurement

Matter and Its Classification

Chemistry studies matter, which is anything that occupies space and has mass. Matter can be classified based on its composition and properties.

• Element: A pure substance consisting of only one type of atom (e.g., O2).

• Compound: A substance formed from two or more elements chemically combined in a fixed ratio (e.g., H2O, CO2).

• Mixture: A physical blend of two or more substances that retain their individual properties.

  • Homogeneous mixture: Uniform composition throughout (e.g., sugar water).

  • Heterogeneous mixture: Non-uniform composition (e.g., trail mix).

Organization of the Periodic Table

The periodic table organizes elements by increasing atomic number and groups elements with similar properties.

• Rows: Called periods (7 total).

• Columns: Called groups or families (18 total).

• Groups are further subdivided into A (main group) and B (transition metals).

• Diagonal line from Boron to Astatine separates metals from non-metals; elements along this line are metalloids.

Physical and Chemical Changes

Matter can undergo physical or chemical changes:

• Physical change: Alters the state or appearance but not the chemical identity (e.g., melting ice).

• Chemical change: Involves the formation of new substances via chemical reactions (e.g., 2H2 + O2 → 2H2O).

Conservation of Matter

The law of conservation of matter states that matter is neither created nor destroyed in a chemical reaction. Thus, the mass of reactants equals the mass of products.

Measurement and SI Units

Measurements in chemistry use the International System of Units (SI). Common prefixes and their relationships to base units are as follows:

Prefix	Abbreviation	Relationship to Base Unit
giga	G	× 1,000,000,000
mega	M	× 1,000,000
kilo	k	× 1,000
deci	d	÷ 10
centi	c	÷ 100
milli	m	÷ 1,000
micro	μ or mc	÷ 1,000,000
nano	n	÷ 1,000,000,000

Significant Figures

Significant figures reflect the precision of a measurement. The following rules apply:

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros are significant only if there is a decimal point.

Rule	Measurement	Number of Significant Figures
Not a zero	41.9	3
Zero between nonzero digits	101.1	4
Zero at the end with decimal	0.030 L	2
Zero at the beginning	0.033 L	2
Zero in a large number without decimal	3,450,000 km	3

Rules for Calculations:

• Addition/Subtraction: Result should have the same number of decimal places as the measurement with the fewest decimal places.

• Multiplication/Division: Result should have the same number of significant figures as the measurement with the fewest significant figures.

Mass, Weight, and Volume

• Mass: The amount of matter in an object (measured in grams).

• Weight: The force exerted by gravity on an object ($\text{Weight} = \text{Mass} \times \text{Gravity}$).

• Volume: The amount of space occupied by matter (measured in liters or cubic centimeters).

Density and Specific Gravity

Density is the ratio of mass to volume:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Units: g/mL or g/cm3

• Density and volume are inversely related.

Specific gravity is the ratio of the density of a substance to the density of water.

Temperature Scales

Temperature can be measured in Celsius (°C), Kelvin (K), or Fahrenheit (°F). Conversion formulas:

$^\circ\text{C} = (\text{F} - 32^\circ\text{F}) \times \frac{1^\circ\text{C}}{1.8^\circ\text{F}}$

$^\circ\text{F} = (1.8^\circ\text{F}/1^\circ\text{C}) \times ^\circ\text{C} + 32^\circ\text{F}$

Energy

• Energy: The capacity to do work or supply heat.

• Potential energy: Stored energy.

• Kinetic energy: Energy of motion.

• Law of conservation of energy: Energy can be converted from one form to another but cannot be created or destroyed.

• SI unit: Joule (J).

• Calorie (cal): Amount of energy required to raise the temperature of 1 g of water by 1°C. 1 Calorie (nutritional) = 1000 calories.

Accuracy and Precision

• Accuracy: How close a measurement is to the true value.

• Precision: How close repeated measurements are to each other.

• Measurements can be precise but not accurate.

Chapter 2: Radioactivity and Radioisotopes

Introduction to Radioactivity

Radioactivity is the spontaneous emission of particles or energy from unstable atomic nuclei. It has applications in medicine, archaeology, and food preservation, but can also be harmful.

Isotopes

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Some isotopes are stable; others are radioactive.

Forms of Radiation

Emission	Symbol	Charge
Alpha	α or 4He	2+
Beta	β or 0e	1-
Gamma	γ	0
Positron	β+	1+
Neutron	n	0

• Alpha particles are positively charged.

• Beta particles are negatively charged.

• Gamma rays are neutral.

• Positrons are positively charged; neutrons have no charge.

Biological Effects of Radiation

Type	Travel Distance Through Air	Tissue Penetration	Protective Shielding
Alpha (α)	A few centimeters	Stops at skin surface	Paper, clothing
Beta (β)	A few meters	Will not penetrate past skin layer	Heavy clothing, plastic, aluminum foil, gloves
Gamma (γ)	Several hundred meters	Fully penetrates body	Thick lead, concrete, water
X-ray	Several meters	Penetrates tissue but not bone	Lead apron, concrete barrier
Neutron (n)	Hundreds to thousands of meters	Fully penetrates body	Concrete barrier, water layer

Radiation Sickness and Exposure

Exposure in mrem	Clinical Effect
5,000–20,000	Cannot be detected
20,000–50,000	Temporary decrease in white blood cells (WBCs)
50,000–100,000	Mild radiation sickness; large decrease in WBC, nausea, vomiting
100,000–200,000	Light radiation poisoning; delayed symptoms, recovery in 3 months
200,000–300,000	Moderate poisoning; hair loss, fatigue, general illness, permanent sterility possible
300,000–400,000	LD50; lethal dose for half the population after 30 days

Units of Radioactivity

Unit	Relationship to Other Units
Becquerel (Bq)	1 Bq = 1 disintegration per second
Curie (Ci)	1 Ci = 3.7 × 1010 disintegrations per second
Millicurie (mCi)	1 Ci = 1,000 mCi
Microcurie (μCi)	1 Ci = 1,000,000 μCi

Radioisotope Half-Lives

The half-life of a radioisotope is the time required for half of the radioactive atoms to decay. This property is used in applications such as radiometric dating and medical diagnostics.

Radioisotope	Symbol	Physical Half-Life
Hydrogen-3 (tritium)	3H	12.3 years
Carbon-14	14C	5730 years
Radium-226	226Ra	1600 years
Uranium-238	238U	4.5 billion years

Nuclear Equations and Decay

Nuclear equations represent the changes that occur during radioactive decay. The general form is:

$\ce{^{A}_{Z}X -> ^{A'}_{Z'}Y + ^{a}_{z}x}$

• A: Mass number (protons + neutrons)

• Z: Atomic number (protons)

• X: Parent nuclide

• Y: Daughter nuclide

• x: Emitted particle (e.g., α, β, γ)

Example: Carbon-14 decay: $\ce{^{14}_{6}C -> ^{14}_{7}N + ^{0}_{-1}e}$

Additional info: The notes also mention units such as the gray (Gy) for absorbed dose and the sievert (Sv) for biological effect, which are important in radiation safety.