Changes in Matter

Just because everything is different doesn't mean anything has changed.

Irene Peter

Definitions to Know:

• Property - a characteristic that describes matter.

• Physical Property - a property that can be observed using one of the five human senses: touch, taste, smell, sight or sound, or, in an extended sense, detected through any measuring device. It can be determined without changing something chemically. Examples are mass, volume, density, color

• Chemical Property - a property used to characterize materials in reactions that change their identity. Examples are burning, rusting

• Substance - a pure type of matter

• Physical Reaction / Physical Change - a change in a substance that does NOT cause something new and different to be formed.

• Chemical Reaction / Chemical Change - a change in a substance caused by the re-arrangement of atoms. This causes a new substance with different properties to form.

• Mixture - a substance consisting of two or more substances mixed together (not in fixed proportions and not with chemical bonding)

• Bonding - the phenomenon of atoms being held together in molecules. This happens with the valence electrons.

• Valence Electron - electrons in the outmost energy level
• Energy level - The path of a given electron's orbit around a nucleus, it is a specifict distance from the nucleus.

• Covalent Bond - a chemical bond between two atoms formed by the sharing of electrons

• Ionic Bond - a chemical bond between ions resulting from the transfer of electrons from one of the bonding atoms to the other.

• Compound - a chemical substance formed from two or more elements, with a fixed ratio determining the composition

• Molecule - the smallest division of a compound that still retains or exhibits all the properties of the substance.

• Formula - an abbreviation for a compound; the number and kind of atoms that make up a molecule of material.

• Chemical Equation - a short, easy way to show chemical reactions, using symbols instead of words. An equation uses the symbols on the left of the equation showing the substances before (reactants), and those on the right those after (products), the reaction.

• Balanced Equation - an equation in which both sides of the equation contain equal numbers of atoms of each element.

• Product - a chemical substance formed as a result of a chemical reaction

• Reactant - a chemical substance that is present at the start of a chemical reaction

• Endothermic - a reaction which absorbs energy

• Exothermic - a reaction which releases energy

 

Physical Changes

• Changes that do not involve chemical nature
• No new substance is formed
• Can be reversed physically
• Changes in physical properties

  • Changes in state

Chemical Changes

• Valence Electrons

  • Electrons in the outer energy level
    • K - 2
    • L - 8
    • M - 18
    • N - 36
  • Where bonding occurs
• Bonding

  • Sharing, gaining, losing of electrons between atoms
  • Causes atoms to combine
• Signs of a chemical change

  • Gas is produced
  • Solid is formed
  • Color change
  • Energy change
• Representing chemical changes

  • Chemical equations
  • Coefficient - represents number of molecules
  • Subscript - represents number of atoms in a molecule
  • The products show what goes into a reaction
  • The reactants show the results of a reaction

  

• Types of chemical changes
  • Synthesis

    • A + B --> AB
  • Decomposition

    • AB --> A + B
  • Replacement

    • AB + CD --> AC + BD