CHEMISTRY #4

• An atom is the smallest particle of an

  element that retains its identity in a

  chemical reaction.
• Democritus’s Atomic Philosophy: The Greek philosopher Democritus

  (460 BC –370 BC) was among the first

  to suggest the existence of atoms.
• Democritus reasoned that atoms

  were indivisible and indestructible.
• Dalton’s Atomic Theory: The modern process of discovery

  regarding atoms began with John

  Dalton (1766–1864), an English

  chemist and schoolteacher.
• Basic Laws of Matter:

  Law of conservation of mass (Lavoisier), Law of definite

  proportions (Proust), Law of multiple proportions (Dalton)
• Law of conservation of mass (Lavoisier):

  Mass is neither created nor destroyed in a chemical

  reaction.
• Law of definite proportions (Proust):A given compound always contains exactly the same proportion of elements by mass.
• Law of multiple proportions (Dalton):

  When two elements combine with each

  other to form two or more compounds, the

  ratios of the masses of one element that

  combines with the fixed mass of the other

  are simple whole numbers.
• Atomic Structure: Atoms consist of three basic particles:

  protons, electrons, and neutrons.
• Molecule

  -is a group of two or more atoms held

  together by attractive forces known as

  chemical bonds.