Rev#1_Chemistry Pt. 1

• Chemistry


  A science that studies matter, its properties, structure and the changes it undergoes together with the energy involved
• Branches of Chemistry

  • Analytical Chemistry
  • Physical Chemistry
  • Inorganic Chemistry
  • Organic Chemistry
  • Biochemistry
• Scientific method


  A systematic approach/procedure in investigating nature; a combination of observations, experimentation and formulation of laws, hypotheses and theories; an organized approach to research
• Steps in a scientific method

  1. Observation or Data Gathering

  2. Are the observations answerable by any natural law?

  3. Defining a problem

  4. Formulate a possible solution (Hypothesis Making)

  5. Experimentation

  6. Interpret results

  7. Generate a generalization
• Observation


  Things perceived by the senses; can be quantitative or qualitative
• Qualitative observation


  Consist of general observations about the system
• Quantitative observation


  Consist of numbers obtained by various measurements of the system
• Inference


  Interpretation of the observation
• Law (natural law)


  A pattern or consistency in observation of natural phenomena; a verbal or mathematical statement which relates a series of observation
• Hypothesis


  An educated guess to explain an observation; a tentative explanation of a natural law based on observation
• Theory


  A hypothesis that survived testing through experimentation; a model or a way of looking at nature that can be used to explain and make further predictions about natural phenomena
• Significant figures


  Rules used to determine the number of significant figures in a measurement
• Types of significant figures

  • Non-zero digits (all non-zero digits are significant)
  • Trailing zeros (final zeros after a decimal point are always significant)
  • Captive zeros (zeros that are found between any two non-zero digits are significant)
  • Leading zeros (zeros before a decimal point are not significant, zeros after the decimal point preceding other digits are not significant)
  • Final zeros in a whole number (may or may not be significant)
• Exact numbers


  Any number that is exact such as the number 3 in the statement "there are three feet in one yard" is said to have unlimited number of significant figures
• Addition and subtraction


  The sum or difference should have the same number of digits to the right of the decimal point as the factor with the least number of digits to the right of the decimal point
• Multiplication and division


  The result obtained by multiplication and/or division must have the same number of significant figures as the factor with the least number of significant figures
• Rules for rounding off numbers

  • If the digit to be removed is less than 5, drop this digit and leave the remaining numbers unchanged
  • If the digit to be removed is equal to or greater than 5, drop this digit and increase the preceding digit by one
• Accuracy


  Nearness of a value to the true or actual value, measured by percentage error
• Precision


  Agreement among different measurements of the same event, measured by deviation
• Types of matter

  • Pure substances
  • Mixture
  • Element
  • Compounds
• Pure substance


  Homogeneous matter that cannot be into its components by physical means; with fixed composition and distinct properties
• "In different compounds of the same elements, the different masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers."
• Historical development of the atom

  • Greeks (400 BC) - Matter was composed of 4 fundamental substances: FIRE, EARTH, WATER, AIR
  • Leucippus and Democritus (5th BC) - First to propose that matter is made up of tiny indivisible particles called "atomos" meaning indivisible
  • Lucretius and the Greeks (1 BC) - What appears as a solid object may actually consist of small particles, there must be some limit to the number of subdivisions which can be formed on any bit of matter, matter can be resolved ultimately into a unit which is indivisible and indestructible
• Dalton's atomic theory


  1. Matter consists of tiny particles called atoms which are indestructible. 2. All atoms in a given element are identical and have the same mass. 3. Atoms of different elements have different properties. 4. Reactions involve only the rearrangement of atoms; separation or union. When atoms combine to form compounds, the ratio of the no. of combining atoms is fixed.
• Thompson's raisin bread/plum pudding model


  The atom contains negatively charged electrons spread over a positive sphere
• Types of chemical changes

  • Synthesis/Combination - Formation of a bigger compound from simpler ones
  • Decomposition - A single compound is broken down to 2 or more simpler substances
  • Single Displacement - Cation or anion is replaced by an uncombined element
  • Double Displacement - Exchange of partners
• Other types of chemical reactions

  • Combustion - Reaction with O₂ to form CO2, H2O, N₂ and oxides of any other elements present
  • Precipitation - Formation of a precipitate when a solution is added to another
• Solubility rules

  • All nitrates are soluble
  • All acetates are soluble
  • All NH4* salts are soluble
  • All salts of Group 1 are soluble
  • All chlorides are soluble except chlorides of Hg22*, Pb²* and Ag*
  • All bromides are soluble except bromides of Hg22+, Pb²* and Ag*
  • All iodides are soluble except iodides of Hg2+ Hg22*, Pb2+ and Ag*
  • Most sulfates are soluble except Group 2, Pb2+ and Hg²+
  • All phosphates are insoluble except NHẬ* and Group 1
  • All chromates are insoluble except NH4* and Group 1
• Neutralization


  Reaction between an acid and a base forming water and salt
• Laws of chemical combination

  • Law of Conservation of Mass - In a chemical reaction, the total mass of the starting materials (reactants) is equal to the total mass of the materials produced (products)
  • Law of Definite Proportion or Composition - Any sample of a pure chemical substance contains the same elements in the same definite proportion by mass of its elements
  • Law of Multiple Proportion - When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers
• Types of solids

  • Crystalline solids - high degree of cohesiveness and very orderly arrangement of particles
  • Amorphous/non-crystalline solids - disordered arrangement of particles but with a high degree of cohesiveness
  • Liquid crystals - medium degree of cohesiveness and very orderly arrangement of particles; allows a degree of ordered motion of particles
• Properties of matter

  • Physical - Extensive/Extrinsic, Intensive/Intrinsic
  • Chemical
• Extensive properties


  Properties that depend on the amount of material observed, e.g. mass, volume, texture
• Intensive properties


  Properties that do not depend on the amount of material observed, e.g. density, odor, taste
• Extrinsic properties


  Properties that can vary with different samples of the same material, e.g. mass, volume, size
• Intrinsic properties


  Properties which are inherent to the substance and do not change
• Crystalline solids


  High degree of cohesiveness and very orderly arrangement of particles
• Amorphous/non-crystalline solids


  Disordered arrangement of particles but with a high degree of cohesiveness
• Liquid crystals


  Medium degree of cohesiveness and very orderly arrangement of particles; allows a degree of ordered motion of particles
• Special forms based on arrangement of particles and the degree of cohesiveness

  • Crystalline solids
  • Amorphous solids
  • Liquid crystals