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Theories of Matter

Theories of Matter. Solids. usually rigid, having definite shape and volume. Liquids. definite volume assume shape of containers but may not fill them can flow under influence of force. Gases. low density can flow can completely fill its container easily compressed and rarified.

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Theories of Matter

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  1. Theories of Matter

  2. Solids • usually rigid, having definite shape and volume

  3. Liquids • definite volume • assume shape of containers but may not fill them • can flow under influence of force

  4. Gases • low density • can flow • can completely fill its container • easily compressed and rarified

  5. Plasmas • exist when the particles of matter have enough kinetic energy that at least some of their electrons become stripped away • very high temperatures

  6. Plasmas • fluid-like, as gases or liquids • consist of a neutral mixture of electrons and positively charged particles

  7. States of Matter • solids, liquids, and gases have been understood for centuries • states of matter are difficult to define with precision

  8. Particles of Matter • Elements: the basic chemical building blocks of matter • cannot be broken down into simpler substances by ordinary means

  9. Particles of Matter • John Dalton developed atomic theory—matter is made up of atoms • now know that atoms can be subdivided

  10. Particles of Matter • Protons: positively charged particles, found in the nucleus of an atom • Neutrons: neutral particles found in the nucleus of an atom

  11. Particles of Matter • Electrons: negatively charged particles occupying a region of space around the nucleus • 1/1860 the mass of a proton

  12. Particles of Matter • Elementary particles: these make up protons, neutrons, and electons • quarks are an example • not fully understood

  13. Particles of Matter • atoms can combine: • molecules • formula units • chemical compounds

  14. Particles of Matter • Ions: charged particles consisting of one or more atoms with a mismatch between the total numbers of protons and electrons

  15. inconvenient to measure in grams or kilograms • relative mass unit • atomic mass unit (amu) • unified atomic mass unit (u) Atomic Mass

  16. Mole: amount of a substance containing 6.022 × 1023 particles • Avogadro’s constant (NA) or Avogadro’s number Atomic Mass

  17. A carbon-12 atom has a mass of 12.00 u. Avogadro’s number of carbon-12 atoms will have a mass of 12.00 g. Atomic Mass

  18. Gas Pressure • Ideal gas model is a good illustration of the kinetic theory • Pressure = sum of impulsive forces divided by area of sides

  19. Gas Pressure • more atoms in the container → greater pressure • smaller “area” on which to exert force → greater pressure

  20. 2mv F = Δt Gas Pressure • greater speed (kinetic energy) of atoms in the container → greater pressure

  21. Kinetic Theory • The particles in solids are held rigidly with strong intermolecular force. • These particles can vibrate in place.

  22. Kinetic Theory • The velocity of these vibrations determines the particles’ kinetic energy. • Large amounts of kinetic energy are indicated with high temperatures.

  23. Kinetic Theory • Liquids have particles in close association but with more mobility.

  24. Kinetic Theory • Cohesion: intermolecular attraction similar particles in a liquid have for each other

  25. Kinetic Theory • Adhesion: intermolecular attraction between particles of dissimilar materials

  26. Kinetic Theory • The kinetic theory of matter considers matter as a collection of numerous, extremely tiny particles in continuous motion.

  27. Kinetic Theory • Although the kinetic theory of matter has limitations, it does a good job predicting the behavior of matter under many conditions.

  28. States of Matter

  29. Arrangement • Crystalline solids: particles are held in fixed patterns • unit cell • NaCl is a good example • most metals

  30. Arrangement • Amorphous solids: particles do not form repeating patterns • glass • Heterogeneous solids: have combination of crystalline and amorphous solids

  31. Elastic Modulus • Solids can change shape in response to certain forces • Tensile forces tend to pull apart

  32. F σ = A Elastic Modulus • Stress (σ): related to the tension force normal (perpendicular) to the cross-sectional area • Defined: force per unit area

  33. Δl ε = li Elastic Modulus • Strain (ε): amount stretched (Δl) divided by the initial length (li) • usually expressed as a simple decimal or percent

  34. σ E = ε Elastic Modulus • Elastic modulus (E): ratio of the normal stress to the linear strain • units: N/m² • plural: elastic moduli

  35. Elastic Modulus • determined experimentally and listed in tables for various substances • measure of a material’s resistance to change in shape (stiffness)

  36. F·li Δl = AE Elastic Modulus • If a wire’s elastic modulus, cross-sectional area, initial length, and the tension exerted on it are known, the change in length can be estimated:

  37. Forces • Compressive forces: crush or push particles of matter together • Shearing forces: tend to cause layers of particles within the solid to slide parallel to each other

  38. shear stress G = shear strain Shear Modulus • Shear stress equals the force exerted parallel to the surface, divided by the surface area. • Shear modulus (G) is the ratio of shear stress to shear strain: • Shear strain is the ratio of deformation of the object parallel to the force, divided by the separation of the two surfaces.

  39. Stress-Strain Graph

  40. Stress-Strain Graph • Proportional limit: maximum strain without permanent deformation

  41. Stress-Strain Graph • Elastic limit: limit of reversible deformation

  42. Stress-Strain Graph • At the fracture point, the object breaks.

  43. Stress-Strain Graph • Materials work harden when stress is applied in a cyclic way, causing them to become harder or more brittle. • This changes the stress-deformation curve.

  44. Transitions • Melting: from solid to liquid • The melting point is usually a predictable temperature at which this occurs

  45. Transitions • Melting: from solid to liquid • A solid’s molecules gain (absorb) enough kinetic energy to break out of their rigid arrangements and move more freely

  46. Transitions • Melting: from solid to liquid • The melting point of a solid also depends on the pressure • Water has unusual properties

  47. Transitions • Water expands when it freezes. • higher pressures hinder freezing • Regelation: melting under pressure

  48. Fluids • Liquids and gases are both classified as fluids. • no fixed shape • assume the shape of their containers • can flow under the influence of a force

  49. Surface Tension • Cohesion at the surface of a liquid pulls the molecules at the surface toward the interior. • The net force is inward. • This is especially evident with polar molecules like water.

  50. Surface Tension • explains why water forms into droplets • meniscus • overflow a glass with water

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