CMH 101 Luca Preziati Chapter 5: Atomic Theory Dalton’s Atomic Theory 1.Elements are composed of atoms – tiny, hard, unbreakable, spheres 2.All atoms of an element are identical 3.Atoms combine in simple, whole-number ratios to form molecules of compounds 4.In chemical reactions, atoms are not broken or changed into another type. Just rearranged. Dalton was able to determine the relative masses of the atoms Dalton based his scale on H = 1 amu we now base it on C-12 = 12 amu exactly unit = atomic mass unit (amu or dalton) John Dalton ( )

Chapter 5: Atomic Theory Subatomic Particle StructureMassCharge Neutron ≈ 1 amu 0 Proton≈ 1 amu+ 1 Electron≈ 0- 1 e-e-

Chapter 5: Atomic Theory Rutherford’s Experiment 1909

Chapter 5: Atomic Theory Isotopes: Atoms with the same number of protons but different number of neutrons. Isotopes have nearly identical chemical properties. The neutrons contribute mass and stability to the nucleus. If a nucleus has has too few or too many neutrons, it becomes radioactive (unstable). Isotopes H 3 1 A = Mass number Z = Atomic number Symbol of element tritium Common name for this isotope A = Z + number of neutrons

Chapter 5: Atomic Theory Ions Atoms acquire a charge by gaining or losing electrons not protons!! Ion Charge = # protons – # electrons Ions with a + charge are called cations more protons than electrons form by losing electrons Ions with a – charge are called anions more electrons than protons form by gaining electrons

Chapter 5: Atomic Theory Mendelev (1834 – 1907) In 1869, the Russian chemist Dmitri Mendeleev arranged the 63 known elements in order of increasing atomic weight starting with hydrogen (later the elements were arranged by atomic number). Arranged the elements into rows (periods) and found lithium, sodium, potassium started new rows; the properties repeated. The Periodic Table

Chapter 5: Atomic Theory

Properties of metals: Solid at room temperature (except for mercury) Shiny Conduct electricity Ductile (can be drawn into wires) Malleable (can be hammered and rolled into sheets) Form alloys with other metals Give up electrons in chemical reactions Metals

Chapter 5: Atomic Theory Nonmetals Properties of non-metals: Poor conductors of electricity (with the exception of graphite) Poor conductors of heat Tend to gain electrons in chemical reactions with metals (with the exception of the unreactive noble gases) Can either be solid, liquid or gas at room temperature. Eleven are gases and one (bromine) is a liquid at room temperature

Chapter 5: Atomic Theory Metalloids There are 8 elements that are classified as metalloids with properties intermediate between those of metals and non-metals. These elements are in a zigzag band between the metals and non-metals in the Periodic Table. These elements are boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine. The last two are radioactive.

Chapter 5: Atomic Theory