Chap 3

Introduction to Chemistry

Title: Chemistry: Concepts and Critical Thinking (8th Edition)

Authors: Charles H. Corwin, John Singer

Focus: Matter and Energy

Matter

Definition

Matter is any substance that has mass and occupies volume, making it an essential component of everything in the physical universe, from the smallest particles to the largest celestial bodies.

Physical States of Matter

Matter exists in three primary states: solid, liquid, and gas, each characterized by distinct properties of particle arrangement and energy.

Kinetic-Molecular Theory

This theory explains the states of matter in terms of the motions and energy of particles, providing a framework for understanding how temperature and pressure affect states.

Solid State

Characteristics

• Shape: Solids have a definite, fixed shape due to tightly packed particles.

• Volume: Solids maintain a definite volume and cannot be compressed significantly.

Kinetic-Molecular Theory

• Particles are tightly packed together in a regular pattern, limiting their movement predominantly to vibrations about fixed positions.

• Energy: Solids have the least energy among the three states of matter, contributing to their stable structure.

Liquid State

Characteristics

• Shape: Liquids have an indefinite shape, taking the shape of their container while maintaining a cohesive volume.

• Volume: Liquids have a definite volume, which remains constant regardless of the container shape and cannot be compressed.

Kinetic-Molecular Theory

• Particles are more loosely packed compared to solids and can move past each other, allowing liquids to flow.

• Energy: Liquids possess more energy than solids but less than gases, giving them the ability to flow while retaining their volume.

Gaseous State

Characteristics

• Shape: Gases have an indefinite shape, completely occupying the shape of their container.

• Volume: Gases have an indefinite volume, which can be significantly compressed, making them highly adaptable to the container they occupy.

Kinetic-Molecular Theory

• Particles are far apart and move freely and rapidly, resulting in minimal attractive forces between them.

• Energy: Gases exhibit the most energy among the three states of matter, facilitating rapid movement and collision between particles.

Physical States of Matter - Table Summary

• Solid: Fixed shape, fixed volume, and not significantly compressible due to tightly packed particles.

• Liquid: Variable shape, fixed volume, and not significantly compressible, maintaining cohesion while enabling flow.

• Gas: Variable shape, variable volume, and significant compressibility, showcasing rapid particle movement.

Changes in Physical States

Many substances can transition between solid, liquid, and gaseous states as temperature changes. For example:

• Water exists as a solid (ice) below 0 °C, a liquid between 0 °C and 100 °C, and a gas (steam) above 100 °C.

Phase Changes

• Solid ↔ Liquid:

  • Melting: The process of a solid turning into a liquid when temperature increases.

  • Freezing: The transformation of a liquid into a solid as temperature decreases.

• Liquid ↔ Gas:

  • Vaporizing: The conversion of a liquid to a gas when temperature rises.

  • Condensing: The change of a gas into a liquid as temperature falls.

• Solid ↔ Gas:

  • Sublimation: A direct transition from solid to gas when temperature increases, commonly observed in substances like dry ice.

  • Deposition: The conversion of a gas directly into a solid as temperature decreases, exemplified by frost formation.

Classifications of Matter

Matter is divided into two primary classes:

• Mixtures: A physical blend of two or more substances that retain their individual properties and can be separated by physical means.

• Pure Substances: Composed entirely of one type of particle, cannot be physically separated; characterized by uniform properties.

Types of Mixtures

• Heterogeneous Mixtures: Exhibit non-uniform properties and composition (e.g., sand mixed with water, where distinct phases are visible).

• Homogeneous Mixtures: Have the same uniform properties throughout (e.g., saltwater, where the solute is evenly distributed).

Pure Substances

• Compounds: Composed of two or more elements chemically combined in fixed proportions (e.g., water = hydrogen + oxygen), can be separated only by chemical reactions.

• Elements: Fundamental substances that cannot be broken down into simpler substances through ordinary chemical methods and are organized in the periodic table.

Occurrence of Elements

• There are over 100 known elements in nature, with 81 considered stable.

• Notably, 10 elements make up more than 95% of the mass of Earth’s crust, water, and atmosphere, underscoring their significance.

Elements in the Human Body

• Oxygen: The most abundant element, not only on Earth but also within the human body, playing a crucial role in respiration.

• Silicon: The second most abundant in the Earth's crust, while carbon is the second most abundant in the human body, essential for life as it forms the basis of organic molecules.

Names of Elements

Each element possesses a unique name often derived from Greek, Latin, or other languages, reflecting their historical context (e.g., Hydrogen from Greek meaning "water former").

Element Symbols

To simplify communication about elements, each is represented by a one- or two-letter symbol (e.g., Gold = Au). The first letter is always capitalized with the second remaining lowercase in cases of two-letter symbols.

Types of Elements

• Metals: Typically have high melting points, excellent conductivity for heat and electricity, and are malleable and ductile, making them useful in various industries.

• Nonmetals: Generally have low melting points, poor conductivity, and are often brittle in solid form, playing crucial roles in biological processes.

• Semimetals (Metalloids): Exhibit intermediate properties between metals and nonmetals, making them valuable as semiconductors in electronics.

Summary of Properties

Comparison of metals and nonmetals based on various categories such as physical state, appearance, malleability, ductility, conductivity, density, and reactivity provides insight into their distinct behaviors and applications.

Periodic Table of the Elements

The periodic table is a systematic organization of elements based on increasing atomic number, grouping elements with similar properties, which provide predictive insight into their behavior.

Law of Definite Composition

This law states that any given compound always contains the same elements in a fixed proportion by mass, emphasizing the consistency of chemical composition regardless of the sample size or source.

Chemical Formulas

A chemical formula succinctly represents the types and numbers of atoms of each element present in a compound, crucial for conveying chemical information in scientific contexts.

Writing Chemical Formulas

Chemical formulas utilize subscripts to indicate the number of atoms present (e.g., H2SO4 represents sulfuric acid), where a subscript of '1' is often omitted.

Interpreting Chemical Formulas

Parentheses may be employed for clarity when denoting complex molecular compositions (e.g., C2H4(OH)2 to show specific arrangements of atoms).

Physical and Chemical Properties

• Physical Properties: Observable characteristics of substances that do not alter their composition, including aspects like physical appearance, melting point, odor, and density.

• Chemical Properties: Describe the behavior of substances during chemical reactions, indicating how they interact with other substances.

Physical and Chemical Change

• Physical Change: Involves alterations in physical state or appearance without changing the chemical identity of the substance (e.g., ice melting to water).

• Chemical Change: Involves a transformation in the composition of the substance, resulting in the formation of new substances (e.g., iron rusting).

Evidence for Chemical Changes

Key indicators of a chemical change can include:

• Release of gas (bubbles or fumes).

• Emission of light or heat.

• Permanent color change.

Conservation Laws

• Conservation of Mass: States that the total mass of substances before a chemical change equals the total mass after, affirming that mass is neither created nor destroyed.

• Conservation of Energy: Energy cannot be created or destroyed, only transformed from one form to another (exemplified mathematically in E = mc^2), highlighting the interconnectedness of energy and mass.

Forms of Energy

Energy exists in various forms, with six key types including:

• Heat: Energy related to temperature and molecular motion.

• Light: Energy carried by electromagnetic waves.

• Chemical: Energy stored in chemical bonds, released during reactions.

• Electrical: Energy resulting from the flow of electric charge.

• Mechanical: Energy related to motion and position.

• Nuclear: Energy released during nuclear reactions.

Conclusion and Chapter Summary

In summary, matter exists in three primary physical states—solid, liquid, and gas—each with unique properties and behaviors. Substances can be classified as mixtures or pure substances, and their distinct characteristics significantly influence their utilization and interaction within the natural world. Additionally, energy and mass are conserved during both physical and chemical changes, underscoring fundamental principles of chemistry.