CH 3

CHM 010 Chapter 3: Matter & Energy, Atoms & Molecules

Learning Goals

This chapter covers fundamental concepts in chemistry, including:

  1. Scientific method

  2. Law of Conservation of Mass and Energy

  3. Differences between physical and chemical properties

  4. Differences between homogeneous and heterogeneous matter, mixtures and compounds, and compounds and elements

  5. Differences between atoms and molecules

  6. Law of Definite Composition (or Definite Proportions)

  7. Understanding atomic mass, formula mass, and molecular mass

  8. Calculating the formula or molecular mass of a compound from its formula

The Scientific Method

The scientific method is a systematic and logical approach to discovering knowledge about the natural world. The steps include:

  • Observation and Classification: Noticing phenomena and categorizing them based on observable criteria.

  • Generalization: Forming hypotheses based on observations.

  • Asking Questions: Inquiries based on observations to drive further investigation.

  • Background Research: Gathering existing information relevant to the question posed.

  • Hypothesis Construction: Formulating a testable educated guess to explain observations.

  • Experimentation: Conducting experiments to test the hypothesis.

  • Data Analysis: Interpreting results obtained from experiments.

  • Conclusion Drawing: Establishing whether the hypothesis is supported or refuted by the experimental data.

  • Reporting Results: Sharing findings with the scientific community.

Study of Chemistry

Chemistry is defined as the study of matter, which encompasses everything that occupies space and has mass, including all physical substances encountered in daily life. Chemistry involves understanding matter's changes and interaction with energy. \n

  • Matter: Anything that occupies space and has mass; includes solids, liquids, gases, and plasma.

  • Energy: Capability to perform work, manifesting in forms like heat and light.

States of Matter

Matter primarily exists in three states: solid, liquid, and gas, with a fourth state known as plasma.

  • Solids:

    • Definite shape

    • Definite volume

    • Particles arranged closer together in a fixed structure

    • Strong interactions between particles, resulting in very slow movement

    • Examples: Ice, salt, iron

  • Liquids:

    • Takes the shape of its container, but has a definite volume

    • Particles are close but arranged randomly

    • Strong interactions with moderate particle movement

    • Examples: Water, oil, vinegar

  • Gases:

    • Fills the entire volume of its container

    • Particles are far apart and randomly arranged

    • Weak interactions, allowing for fast movement

    • Examples: Water vapor, helium, air

  • Plasma: A state comprising electrically charged atomic particles, characterized by free-moving ions and electrons, found in stars and lightning.

Classification of Matter

Matter can be classified as either homogeneous or heterogeneous:

  • Homogeneous Matter:

    • Same composition and properties throughout (e.g., solutions).

    • Examples: Brass (homogeneous mixture), sugar dissolved in water (uniform composition).

  • Heterogeneous Matter:

    • Different compositions with varying properties throughout (e.g., mixtures).

    • Examples: Sand mixed with iron filings; the composition differs visibly.

Pure Substances: Elements and Compounds

  • Pure Substances: Matter with fixed composition, can be categorized into:

    • Elements: Composed of one type of atom (e.g., Cu for copper, Pb for lead).

    • Compounds: Composed of two or more elements in a definite ratio (e.g., NaCl for table salt, H2O for water).

Differences Between Elements and Compounds

  • Elements cannot be broken down into simpler substances without losing their properties.

  • Compounds can be decomposed into their constituent elements through chemical reactions (e.g., NaCl into sodium and chloride).

Mixtures

Mixtures can be classified as either homogeneous or heterogeneous, consisting of two or more substances mixed but not chemically combined.

  • Homogeneous Mixtures: Uniform composition; parts not visible (e.g., air, sugar water).

  • Heterogeneous Mixtures: Non-uniform composition with visible different parts (e.g., salad, pasta with sauce).

Physical and Chemical Properties

  • Physical Properties: Observed or measured without changing the chemical composition, including state, shape, color, and boiling/melting points. Example: A penny has a reddish color and a shiny luster.

  • Chemical Properties: Describe a substance’s ability to undergo chemical changes to form new substances (e.g., ability of iron to rust).

  • Physical Changes: Alter physical properties without changing chemical composition, such as boiling water or dissolving sugar.

  • Chemical Changes: Original substances are transformed into new substances (e.g., frying an egg or burning wood).

Law of Conservation of Mass and Energy

  • Law of Conservation of Mass: In a chemical reaction, mass is conserved; the total mass of reactants equals the total mass of products.

  • Law of Conservation of Energy: In physical or chemical changes, energy is neither created nor destroyed but transformed from one form to another (e.g., potential energy converting into kinetic energy).

Types of Energy

  • Potential Energy: Stored energy due to position (e.g., water stored in a dam).

  • Kinetic Energy: Energy of motion (e.g., flowing water).

Elements, Atoms, and Molecules

  • Elements are pure substances that cannot be broken down (e.g., gold, sulfur).

  • Atoms are the smallest units of elements (e.g., a single gold atom).

  • Molecules are combinations of two or more atoms, retaining compound properties (e.g., H2 is a diatomic molecule of hydrogen).

  • Ions: Charged atoms that form ionic compounds through attractive forces between positive and negative ions.

Periodic Table and Chemical Symbols

  • Elements are classified into metals, nonmetals, and metalloids. Examples include:

    • Metals: Gold (Au), Aluminum (Al)

    • Nonmetals: Sulfur (S)

    • Metalloids: Silicon (Si)

  • Chemical Symbols: Abbreviations (one or two letters) for elements; first letter capitalized, second letter lowercase (e.g., Co for cobalt, Na for sodium). Symbols derived from Latin include:

    • Cu (Cuprum) for Copper

    • Au (Aurum) for Gold

    • Fe (Ferrum) for Iron

Chemical Formulas and Atomic Mass

  • A chemical formula represents a substance's composition, such as NaCl for salt.

  • Atomic Mass: Defined as the mass of an atom in atomic mass units (amu); one amu = 1/12 the mass of a carbon-12 atom.

  • Molecular Mass: Sum of atomic masses of all atoms in a molecule; for P2O5, molecular mass = 2×31.0 (P) + 5×16.0 (O).

  • Formula Mass: Similar concept for ionic compounds where you sum the masses of ions included in the formula unit.

Conclusion

Understanding the concepts of matter and energy, atomic structure, and the properties of substances is fundamental for grasping the principles of chemistry. These foundational ideas are crucial for conducting scientific inquiries and recognizing the behavior of various materials in different contexts, preparing students for further studies in chemistry and related fields.