Conservation of Mass

Law of Conservation of Mass

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. This principle is fundamental to all chemical processes.

• Definition: The total mass of reactants equals the total mass of products in a closed system.

• Example: When hydrogen reacts with oxygen to form water, the combined mass of hydrogen and oxygen before the reaction equals the mass of water produced.

Scientific Method

Steps of the Scientific Method

The scientific method is a systematic approach to investigating natural phenomena.

• Observation: Gathering data about phenomena.

• Hypothesis: Proposing a tentative explanation.

• Experimentation: Testing the hypothesis through controlled experiments.

• Analysis: Interpreting data to draw conclusions.

• Conclusion: Accepting, rejecting, or modifying the hypothesis based on results.

Scientific Notation

Expressing Numbers in Scientific Notation

Scientific notation is used to express very large or very small numbers in a compact form.

• Format: , where and is an integer.

• Example: 0.00056 =

Significant Figures

Rules for Significant Figures

Significant figures reflect the precision of a measured quantity.

• 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.

Example: 0.04050 has four significant figures.

Measurement

Accuracy and Precision

Measurement in chemistry involves determining the quantity of a substance using standard units.

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

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

Prefixes/SI Units

International System of Units (SI)

The SI system is the standard for scientific measurements.

• Base Units: meter (m), kilogram (kg), second (s), mole (mol), kelvin (K), ampere (A), candela (cd).

• Common Prefixes:

Unit Conversions (Dimensional Analysis)

Converting Between Units

Dimensional analysis uses conversion factors to change units.

• Conversion Factor: A ratio equal to one that converts one unit to another.

• Example: To convert 5.0 cm to meters:

Density

Definition and Calculation

Density is the mass per unit volume of a substance.

• Formula:

• Units: g/cm3 or kg/m3

• Example: If a block has a mass of 10 g and a volume of 2 cm3, its density is .

Phases of Matter

States and Properties

Matter exists in different physical states, each with unique properties.

• Solid: Definite shape and volume.

• Liquid: Definite volume, takes shape of container.

• Gas: No definite shape or volume, expands to fill container.

Mixtures

Types of Mixtures

Mixtures are combinations of two or more substances that retain their individual properties.

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

• Colloids: Particles are intermediate in size (e.g., milk).

• Heterogeneous Mixture: Non-uniform composition (e.g., salad).

Physical vs. Chemical Change

Distinguishing Changes in Matter

Changes in matter can be classified as physical or chemical.

• Physical Change: Alters form but not composition (e.g., melting ice).

• Chemical Change: Produces new substances (e.g., rusting iron).

Isotopes/Natural Abundance/Atomic Mass

Atomic Structure and Isotopes

Atoms of the same element can have different numbers of neutrons, called isotopes.

• Isotope: Atoms with the same number of protons but different numbers of neutrons.

• Natural Abundance: The relative amount of each isotope in a natural sample.

• Atomic Mass: Weighted average mass of all isotopes of an element.

Formula:

Periodic Table

Organization and Use

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

• Groups: Vertical columns with similar chemical properties.

• Periods: Horizontal rows.

• Metals, Nonmetals, Metalloids: Classified based on physical and chemical properties.

Atomic Structure

Components of the Atom

Atoms are composed of subatomic particles: protons, neutrons, and electrons.

• Proton: Positively charged, located in the nucleus.

• Neutron: Neutral, located in the nucleus.

• Electron: Negatively charged, orbits the nucleus.

Atomic Number (): Number of protons in the nucleus.

Mass Number (): Total number of protons and neutrons.

Example: Carbon-12 has 6 protons and 6 neutrons ().