Comprehensive Chemistry Notes: Scientific Method, Properties, and Periodic Table

What marks the beginning of chemistry?

Humans transforming substances using fire (e.g., cooking, smelting metals).

What is alchemy?

A mix of chemical techniques and mystical ideas aiming to turn base metals into gold and create elixirs.

What are the steps of the scientific method?

Observation → Question → Hypothesis → Experiment → Analysis → Conclusion.

Define hypothesis, theory, and law

Hypothesis: testable guess; Theory: well-supported explanation; Law: describes consistent behavior.

What are the three domains of chemistry?

Macroscopic (visible), Microscopic (atoms/molecules), Symbolic (formulas/equations).

What are the four states of matter?

Solid, liquid, gas, plasma.

Difference between mass and weight?

Mass = amount of matter (unchanging); Weight = gravity's pull on mass (changes with location).

What is the law of conservation of matter?

Matter is not created or destroyed—only changes form.

Define element, compound, and mixture.

Element: pure substance; Compound: two+ elements chemically combined; Mixture: physical blend of substances.

Difference between homogeneous and heterogeneous mixtures?

Homogeneous: uniform throughout; Heterogeneous: uneven composition.

What is an atom?

The smallest unit of an element that retains its properties.

What is a molecule?

Two or more atoms bonded together.

What's the difference between an element and a compound?

Element = one type of atom; Compond = two or more types of atoms.

What happens when water decomposes?

H₂O → H₂ + O₂ (hydrogen and oxygen gases form).

What are fuel-cell vehicles (FCVs)?

Cars powered by hydrogen that produce only water as waste.

How is chemistry used in cell phones?

Phones use ~30% of natural elements—plastics, metals, semiconductors, and battery materials.

What is a physical property?

A trait observed without changing the substance (e.g., color, melting point).

What is a chemical property?

A trait that describes how a substance reacts (e.g., flammability, rusting).

What is a physical change?

A change in form or state without changing the substance (e.g., melting, dissolving).

What is a chemical change?

A change that creates new substances (e.g., burning, cooking, rusting).

Difference between extensive and intensive properties?

Extensive: depends on amount (mass, volume); Intensive: doesn't depend on amount (temperature, density).

What does the NFPA hazard diamond show?

Chemical risks—fire (red), health (blue), reactivity (yellow), special hazards (white), rated 0-4.

What does the periodic table show?

Groups elements by properties—metals, nonmetals, metalloids; also shows state (solid, liquid, gas).

What are the components of a measurement?

Value, unit, and uncertainty.

What are SI units?

Standard units like meters, seconds, kilograms.

What are derived units?

Units like liters (volume), g/cm³ (density).

What do prefixes like micro and mega mean?

Micro = 10⁻⁶; Mega = 10⁶.

Wat is uncertainty in measurement?

Estimate of how much a measurement may differ from the true value.

What are significant figures?

Digits that reflect the precision of a measurment.

What is accuarcy?

Closeness to the true value.

What is precision?

Consistency among repeated measurements.

What is dimensional analysis?

A method to convert units and solve problems using conversion factors.

What is a unit conversion factor?

A ratio of equivalent values used to change units (e.g., 1 inch = 2.54 cm).