Introductory Chemistry Notes ch 1

Chemistry: Introduction and Matter

Introduction to Chemistry

• Chemistry helps us understand the world around us.
• The beautiful colors of the aurora borealis are a result of atmospheric chemistry.
• Solar wind carries charged particles (electrons) toward Earth.
• These particles collide with molecules in the atmosphere, exciting them to higher energy states.
• When the molecules relax back to lower energy states, they emit light of various colors.

Thinking Like a Chemist

• Chemists solve macroscopic problems by understanding the microscopic (molecular) level.
• They design experiments to indirectly explore the molecular level.
• Developing hypotheses is an essential part of this process.
• The scientific method is a stepwise approach to problem-solving applicable in many fields.
• Matter is composed of atoms and molecules (particulate nature of matter).
• The interactions between atoms and molecules lead to different physical states of matter: solids, liquids, and gases.
• Chemists classify matter by determining its composition.
• Distinguishing between mixtures and pure substances is a key task.
• Chemistry involves definitions, theories, hypotheses, and problem-solving, all of which are interconnected.

Matter and Chemistry Defined

• Matter: Anything that has mass and takes up space.
• Chemistry: The science of matter, including its composition, structure, properties, reactions, and energy.
• Chemists devise experiments, interpret data, prepare new substances, and utilize matter's properties to create useful things.
• Much of chemistry deals with entities too small to be observed directly (atoms and molecules).
• Goals of chemistry include understanding matter, solving problems, and developing new substances or materials.

Molecular Representation: Water Example

• Water (H_2O) consists of two hydrogen atoms and one oxygen atom joined by bonds.
• The oxygen atom is in the center with the two hydrogen atoms bonded to it.
• Electrons on the oxygen atom include bonding pairs and lone pairs.
• Oxygen is electronegative, pulling electron density toward itself (partial negative charge, \delta^-.).
• Hydrogens are electropositive, with less electron density (partial positive charge, \delta^+.).
• This charge distribution affects water's behavior and properties like surface tension, freezing, organization, density, and capillary action.

The Scientific Method

• A problem-solving process with several steps:
  • Define the problem: Observe something or conduct an experiment.
  • Collect facts and data: Gather relevant information.
  • Formulate a hypothesis: Create a working model to predict behavior and explain observations.
  • Test the hypothesis: Design experiments to validate or invalidate it.
  • Modify the hypothesis: Refine it to better fit the data, or discard it and start over.

Hypothesis, Theory, and Law

• Hypothesis: A working model used to explain observations and predict behavior.
• Theory: A well-established hypothesis supported by repeated experiments, often by many different people, data should be repeatable.
• Scientific Law: A hypothesis that has been extensively supported under many conditions over time with no known exceptions.

Particulate Nature of Matter

• Matter has mass and takes up space and can be large or as small as an atom.
• Atoms are discrete, tiny, fundamental particles.
• Scanning tunneling microscopes allow viewing of individual atoms in specific configurations.
• Atoms can exhibit repeating arrangements, indicating structure (e.g., silicon atoms on a silicon wafer).

States of Matter

• Three states of matter: solid, liquid, and gas.
• Solid:
  • Has a definite shape and volume, independent of its container.
  • Most solids are crystalline, with particles arranged in a regular, repeating 3D pattern.
  • Particles are held together rigidly and close to one another.
  • Examples: ice, graphite, salt crystals.
  • Crystalline vs. Amorphous:
    • Crystalline: Organized arrangement.
    • Amorphous: Disorganized arrangement (e.g., plastics, glass, gels).
  • Amorphous solids lack a regular 3D arrangement.
  • Glass can be considered a viscous liquid, as evidenced by distortion in very old windows.
• Liquid:
  • Has a definite volume but no definite shape; takes the shape of its container.
  • Particles are fairly close together and held by strong attractive forces.
  • Particles can move freely relative to each other, allowing liquids to flow.
  • Particles in a liquid are still fairly close together and held together by strong attractive forces, but instead of being in a somewhat rigid arrangement, like solids, the particles in a liquid are able to move freely relative to each other.
• Gas:
  • Has indefinite volume and no fixed shape.
  • Can expand and compress.
  • Particles are relatively far apart and move independently.
  • Example: water vapor.

Attractive Forces and Properties

• Atoms and molecules have attractive forces that hold them together.
• Polarity in molecules (example: water) leads to these attractive forces.
• These forces determine matter's appearance and properties.
• Water's unique properties are crucial for life.
• Ranking of attractive forces:
  • Strongest in solids (rigidity).
  • Weaker in liquids (uniform volume).
  • Weakest in gases (independent behavior).
• Closer molecules have stronger attractive forces.

Common Examples of Solids, Liquids, and Gases

• Liquids: alcohol, blood, gasoline, honey, mercury, oil, syrup, vinegar, water.
• Gases: acetylene, air, butane, carbon dioxide, chlorine, helium, methane, nitrogen, oxygen.
• Solids: aluminum, copper, gold, polyethylene, salt (NaCl), sand (silicon dioxide), steel, sugar (C12H22O11), sulfur.

Pure Substances vs. Mixtures

• Pure Substance: Has a definite, fixed composition; either an element or a compound (e.g., pure oxygen, pure water, pure sucrose). Made up of more than one type of atom.
• Mixture: A combination of two or more pure substances.

Homogeneous vs. Heterogeneous Matter

• Homogeneous Matter: Uniform in appearance and properties; looks the same throughout (e.g., sugar dissolved in water).
• Heterogeneous Matter: Two or more physically distinct phases; not well mixed (e.g., ice floating in water -- mixture of two phases).
• Mixture: Combination of two or more pure substances; can be homogeneous or heterogeneous.
• Homogeneous Mixture: The proportions of sugar and water can vary. Homogeneous mixture when the composition will be the same throughout.
• Heterogeneous Mixture: Have different composition at different points. Examples: oil and water is a classic example of a heterogeneous mixture.

Separating Mixtures

• Mixing is not a chemical reaction; substances do not lose their identities and can be separated (e.g., boiling, filtration, flotation, magnetism, crystallization, chromatography).
• Example: Iron shavings and sulfur can be separated using a magnet.

Examples and Classifications

• Baking soda (NaHCO_3) is a compound and a pure substance.
• Gasoline contains about 150 different hydrocarbons.
• Gasoline: Homogeneous mixture (alkanes, alkenes, isoalkanes, cycloalkanes, aromatics).
• Grape juice: Homogeneous mixture (water, sugar, chemical compounds like anthocyanins) if water-soluble and well-strained; otherwise, heterogeneous.
• Copper metal: Element, pure.
• Soil: Heterogeneous mixture (sand, silt, clay, water, nutrients, plant matter, bugs).
• A randomized, well-mixed soil sample not homogeneous

Identifying Homogeneous Mixtures

• Carbon dioxide (CO_2): Compound, not a mixture.
• Mercury: Element, not a mixture.
• Maple syrup: Homogeneous mixture (uniform appearance).
• Concrete: Heterogeneous mixture (aggregate, Portland cement, water, air).
• Italian salad dressing: Heterogeneous mixture (oil, water, spices).
  • Oil and water do not mix.
• A uniform thick brown liquid with no floating substance that doesn't present any difference in appearance in the color at the bottom of the the container versus the top is considered homogenous

Filtration

• Filtration separates a heterogeneous mixture of a liquid and a solid.
• A liquid passes through a filter, while the solid remains on the paper.
• Isolate the solids on the paper and the liquid passes through.
  • A mixture of sand and water is separated, resulting in catching the sand on the paper while passing through the water into the receiving vessel

Chapter Summary

• Definitions
• Scientific method
• Elements and compounds
• Different types of mixtures
• Phases
• Solids, liquids, gases