intro to agri chem

• Basic things of chemistry

  • Matter
  • Atoms
  • Element
  • Compounds
  • Molecules
• Matter


  Any substance that has mass
• Mass


  The quantity of matter within an object
• Weight


  The result of the pull of gravity on an object
• Atoms


  The smallest particle, constructed from neutrons, protons and electrons

  
• Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.
• Elements


  All atoms of an element are identical. Different elements have different weights and different chemical properties.
• Chemical symbol


  The abbreviation for an element
• Compounds


  Elements combine to form chemical compounds. Metals often react with nonmetals to form ionic compounds. Nonmetals combine with each other to form covalent compounds (neutral molecules).
• Molecules


  A group of two or more atoms held together by chemical bonds. Every combination of atoms is a molecule.
• States of matter


  • Solid
  • Liquid
  • Gas
• Solids


  • Definite shape (rigid)
  • Definite volume
  • Molecules closely packed together
  • Particles vibrate around fixed axes
  • Contain the least amount of kinetic energy
• Liquids


  • No definite shape (takes the shape of its container)
  • Has definite volume
  • Particles are free to move over each other, but are still attracted to each other
• Gases


  • No definite shape (takes the shape of its container)
  • No definite volume
  • Particles move in random motion with little or no attraction to each other
  • Highly compressible
• Polarity and dipole moment

  The oxygen atom is more electronegative than the hydrogen atom, giving water a bent shape and a net dipole moment. This allows water molecules to form hydrogen bonds.
• Universal solvent


  Water dissolves many polar and ionic species, but cannot dissolve oils, fats, and some hydroxides.
• High heat capacity


  Water absorbs 4184 Joules of heat per kilogram for its temperature to increase by 1 °C, helping moderate Earth's temperature.
• High heat of vaporization

  Water's high heat of vaporization allows evaporative cooling, as sweat evaporating from the skin carries excessive heat from the body.
• Cohesive property and surface tension

  Water molecules form strong hydrogen bonds, resulting in cohesive forces and a skin on the surface that can resist external forces.
• Adhesive property and capillary action

  Water molecules adhering to container walls cause an upward force and upward meniscus, allowing water and dissolved nutrients to move against gravity, essential for plants and trees.
• Density


  The density of ice is less than water, allowing ice to float on water and insulate the water below from freezing.
• States of water


  • Ice has a dense, hexagonal crystalline structure
  • Liquid water has fewer hydrogen bonds, allowing molecules to move quickly and form a dense structure
  • Gaseous steam has separated molecules with no hydrogen bonds, making it very dangerous when it condenses on skin.
• Freezing and boiling points

  Water freezes at 0 ºC and boils at 100 ºC, requiring massive energy to transform phase, which is vital for the ecosystem and living organisms.
• Chemical and physical changes

  • Chemical change results from a chemical reaction, physical change is when matter changes form but not chemical identity
  • Signs of chemical change include gas production, bubbles, odor, color change, sound, temperature change, light, precipitate
  • Chemical changes are difficult or impossible to reverse, physical changes are often reversible
  • Examples of chemical changes are burning, cooking, rusting, rotting
  • Examples of physical changes are boiling, melting, freezing, shredding