Transcript Chem Notes
Chem Notes Chapter 5 Section 5.1 & 5.2 Early Models of the Atom First proposed by Democritus in the 4th century. Believed atoms were indivisible and indestructible Dalton’s Atomic Theory Came 2000 years later, based on experimentation All elements composed of tiny indivisible particles called atoms Dalton’s Atomic Theory Came 2000 years later, based on experimentation All elements composed of tiny indivisible particles called atoms Atoms of the same element are identical; different from atoms of other elements Dalton’s Atomic Theory Came 2000 years later, based on experimentation All elements composed of tiny indivisible particles called atoms Atoms of the same element are identical; different from atoms of other elements Atoms of different elements can mix or chemically combine in simple wholenumber ratios to form compounds. Chemical rxns occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of another element. Atom: fundamental building block of all matter Smallest particle of an element that retains the properties of that element. Very, very small. Can view images of surface of groups of atoms with scanning tunneling microscope. Subatomic Particles Much of Dalton’s theory still accepted – one notable exception is that atoms are now known to be divisible. Subatomic Particles Electrons Subatomic Particles Electrons Negatively charged Subatomic Particles Electrons Negatively charged Each electron carries one unit of negative charge Subatomic Particles Electrons Negatively charged Each electron carries one unit of negative charge Mass is 1/1840 the mass of a hydrogen atom (or one proton) Subatomic Particles Electrons Negatively charged Each electron carries one unit of negative charge Mass is 1/1840 the mass of a hydrogen atom (or one proton) Discovered by J.J. Thomson in 1897 using cathode ray tubes. Subatomic Particles Protons One unit of positive charge Mass is 1840x that of the electron Subatomic Particles Neutrons No charge, but mass nearly equal to that of protons Existence confirmed by James Chadwick in 1932 Atomic Nucleus Discovered by Rutherford’s gold foil experiments. Atomic Nucleus Discovered by Rutherford’s gold foil experiments. Proposed that an atom is mostly empty space with the positive charge and nearly all mass concentrated in small region. Nucleus – central core of atom; composed of protons and neutrons