CHEMISTRY

• a science that studies matter, its properties, structure and the changes it undergoes together with the energy involved.

  Chemistry
• things perceived by the senses; can be quantitative or qualitative

  observations
• consist of general observations about the system

  qualitative
• consist of numbers obtained by various measurements of the system

  quantitative
•  interpretation of the observation

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

  Natural Law
• 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

  Theory
• Final zeros after a decimal point are always significant.

  e.g. 25.330 g has 5 significant figures

  Trailing Zeros
• Zeros that are found between any two non-zero digits are significant.

  e.g 706.3 mm has 4 significant figures

  Captive Zeros
• • Zeros before a decimal point are not significant.

  e.g 0.786 g has 3 significant figures.

  • When there are no digits before a decimal point or when the digit before a decimal point is zero, the zeros after the decimal point preceding other digits are not significant.

  e.g. 0.000543 cm3 has 3 significant figures

  Leading Zeros
• This in a whole number may or may not be significant.

  To resolve this, use of exponential is recommended.

  Final Zeros
• 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.

  Exact Numbers
• refers to the nearness of a value to the true or actual value.

  Accuracy
•  the difference between a measured value and the true (or most probable) value.

  Error
• percent error = (/Average value – True value/ x 100%)/

          True value 
• Higher percent error, less accurate
•  indication of the agreement among different measurements of the same event.

  precision
• absolute value of the difference of the measured value from the average value

  Deviation
• Higher deviation, less precise
• anything that has mass, takes up space (volume) and possesses inertia

  matter
• homogeneous matter that cannot be separated into its components by physical means; with fixed composition and distinct properties

  Pure Substance
• pure substance composed only of 1 type of atom; cannot be decomposed by ordinary means into simpler substances (Ex. H, He, Au, W)

  Elements
• two or more elements chemically combined in a definite and constant proportion (Ex. KCl, CH3COOH, MgCl2)

  Compounds
• • Structural units are the cations and anions

  Ionic compounds
• Properties of Ionic Compounds 

  Melting Point: High

  Electrical Conductivity: Solid

  Hardness: Very Hard

  Malleability: Brittle
• Uncharged or neutral structural units (molecules) in the crystal lattice.

  Covalent Molecular Substances
• Properties of Covalent Molecular Compounds

  Melting Point: Low

  Electrical Conductivity: Solid

  Hardness: Soft

  Malleability: Brittle
• • The structural units that occupy the lattice points in the solid are ATOMS.
  • The atoms are bound to each other by strong COVALENT BONDS.

  Covalent Network Substances
• Properties of Covalent Network Substances

  Melting Point: Very high

  Electrical Conductivity: Solid

  Hardness: Very Hard 

  Malleability: Brittle
•  combination of different substances in variable proportions; can be separated into its components by physical methods of separation

  Mixture
• uniform composition and properties throughout a given sample, but composition and properties may vary from one sample to another (e. g. solutions)

  Homogeneous
• with non-uniform properties throughout a sample where components retain their identity and phase boundaries exist (e.g. colloids, suspensions)

  Heterogeneous
• rigid, has definite volume and shape phase of matter

  Solid
• phase of matter that is fluid ( has ability to flow), takes the shape of the portion of the container they occupy

  Liquid
• phase of matter that is fluid, expands to fill up its container

  Gas
• high degree of cohesiveness and very orderly arrangement of particles

  Crystalline solids
• disordered arrangement of particles but with a high degree of cohesiveness

  Amorphous solid
• medium degree of cohesiveness and very orderly arrangement of particles; allows a degree of ordered motion of particles

  Liquid crystals
• properties that depend on the amount of material observed

  Extensive Properties
• properties that does not depend on the amount of material observed

  Intensive Properties