The Scientific Method

Overview

The scientific method is a systematic approach used in scientific investigation to acquire new knowledge and validate existing knowledge. It involves making observations, forming hypotheses, conducting experiments, analyzing data, and drawing conclusions.

• Hypothesis: A tentative explanation or prediction that can be tested by experiments.

  • Falsifiable: A hypothesis must be structured so that it can be proven false by evidence.

• Experiments: Controlled procedures carried out to test the validity of a hypothesis.

• Data Analysis: The process of interpreting experimental results to determine if they support or refute the hypothesis.

• Drawing Conclusions: Summarizing findings and determining the next steps, such as revising the hypothesis or developing a theory.

Scientific Laws and Theories

Definitions

• Scientific Law: A concise statement that summarizes a broad variety of observations and experiences. Laws describe what happens under certain conditions but do not explain why.

• Scientific Theory: A well-substantiated explanation of some aspect of the natural world that is based on a body of evidence and has stood up to repeated testing.

States of Matter

Classification and Properties

Matter exists in different physical forms called states or phases. The three primary states are:

• Solid: Has a definite shape and volume. Particles are closely packed and vibrate in place.

  • Crystalline: Particles are arranged in an orderly, repeating pattern (e.g., salt, diamond).

  • Amorphous: Particles lack a long-range order (e.g., glass, plastic).

• Liquid: Has a definite volume but takes the shape of its container. Particles are close but can move past each other.

• Gas: Has neither definite shape nor volume. Particles are far apart and move freely.

Types of Matter

Classification

• Mixture: A physical combination of two or more substances.

  • Homogeneous: Uniform composition throughout (e.g., saltwater).

  • heterogeneous: Non-uniform composition (e.g., salad, sand and iron filings).

• Pure Substance: Matter with a fixed composition. Includes elements and compounds.

Properties and Changes of Matter

Physical and Chemical Properties

• Physical Properties: Characteristics observed without changing the substance's identity (e.g., color, melting point, density).

  • Example: Ice melting to water (change in state, not composition).

• Chemical Properties: Characteristics observed when a substance undergoes a chemical change (e.g., flammability, reactivity).

  • Example: Iron rusting (iron reacts with oxygen to form iron oxide).

Physical and Chemical Changes

• Physical Change: Alters the state or appearance but not the chemical composition.

  • Example: Boiling water (liquid to gas).

• Chemical Change: Alters the chemical structure, resulting in new substances.

  • Example: Burning wood (produces carbon dioxide, water, ash).

Significant Figures

Rules and Applications

• Zeroes that matter:

  • Interior (captive) zeroes: Always significant (e.g., 205 has three significant figures).

  • Leading zeroes: Never significant (e.g., 0.0025 has two significant figures).

  • Trailing zeroes: Significant only if there is a decimal point (e.g., 2.300 has four significant figures).

• Scientific Notation: Used for very large or small numbers to clearly indicate significant figures (e.g., has three significant figures).

• Rounding: Round to the correct number of significant figures based on the operation performed (addition/subtraction: least decimal places; multiplication/division: least significant figures).

Unit Conversions

Dimensional Analysis (Cross Method)

Unit conversions are performed using dimensional analysis, also known as the cross method. This involves multiplying by conversion factors so that units cancel appropriately.

• Example: To convert 10 inches to centimeters:

In-Class Math Review

Sample Calculations

• 3.5 - 2.396 = 1.104

• 2.341 × 376 × 0.007 = 6.16

• (7826 + 23 - 5.2) × 7.5 = 58,627.5

• (5.95 × 3.7628) - 4.25 = 17.12

Additional info: Answers are calculated and rounded to appropriate significant figures.

Laws of Definite and Multiple Proportions

Fundamental Chemical Laws

• Law of Definite Proportions: A given compound always contains the same elements in the same proportion by mass.

• Law of Multiple Proportions: When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

The Structure of the Atom

Subatomic Particles

• Protons: Positively charged particles in the nucleus. The number of protons defines the atomic number ().

• Neutrons: Neutral particles in the nucleus. Number of neutrons = mass number () - atomic number ().

• Electrons: Negatively charged particles in orbitals around the nucleus.

Isotopes

Definition and Calculation

• Isotopes: Atoms of the same element with different numbers of neutrons (and thus different mass numbers).

• Number of Protons: Equal to the atomic number ().

• Number of Neutrons:

• Natural Abundance: The relative percentage of each isotope in a naturally occurring sample of the element.

Reading the Periodic Table

Groups and Ionic Charges

• Groups: Vertical columns in the periodic table. Elements in the same group have similar chemical properties.

• Determining Ionic Charges: Main group elements often form ions with predictable charges based on their group number (e.g., Group 1 forms +1 ions, Group 17 forms -1 ions).

Ions

Types and Naming

• Cations: Positively charged ions (formed by losing electrons).

• Anions: Negatively charged ions (formed by gaining electrons).

• Polyatomic Ions: Ions composed of two or more atoms covalently bonded, carrying a net charge (e.g., , ).

• Determining Charge: Based on the number of electrons lost or gained relative to the neutral atom.

• Naming: Cations use the element name (e.g., sodium ion), anions use the root plus '-ide' (e.g., chloride), and polyatomic ions have specific names (e.g., sulfate, nitrate).

Formula Writing and Naming Compounds

Rules and Examples

• Formula Writing: Combine cations and anions in ratios that yield a neutral compound.

• Naming Compounds: Use systematic rules for ionic and molecular compounds.

  • KI: Potassium iodide

  • Sr(NO3)2: Strontium nitrate

  • Carbon tetrachloride: CCl4

  • Hydrogen sulfate: HSO4- (as an ion) or sulfuric acid (H2SO4)

  • Copper(II) oxide: CuO

  • Co(NO3)2: Cobalt(II) nitrate

  • CaCO3: Calcium carbonate

Additional info: Naming conventions follow IUPAC rules for inorganic compounds.