Lecture 1 Atoms, Atomic Theory, Elements, Intro To Symbols And Formulas
- 1. ATOMS, ATOMIC THEORY, ELEMENTS, INTRO TO SYMBOLS AND FORMULAS Lecture for 10/5/07
- 2. Early ideas of the composition of matter Democritus in 450 BC Aristotle and other well-known Greek philosophers didn’t believe Democritus Atoms are defined in terms of elements An atom is the smallest particle of an element that retains the chemical identity of that element
- 3. 17 th -18 th century – new ideas emerge Antoine Lavoisier Joseph Louis Proust: “ Law of Constant Composition ”(1799) Compounds always contained the same ratio by weight of their elements Concluded that a given compound always has the same composition, no matter where it came from John Dalton : Developed an atomic theory of matter in 1803 (called Dalton’s atomic theory ) Each element is composed of extremely small particles called atoms. All atoms of a given element are identical, but they differ from those of any other element. Atoms are neither created nor destroyed in any chemical reaction. A given compound always has the same relative number and kinds of atoms.
- 4. How can we be sure that atoms exist? Evidence that atoms exist is overwhelming and conclusive Scanning tunneling microscope provides pictures of atoms Chemistry is the study of two worlds – macroscopic and submicroscopic Observations are made in the macroscopic world, however, to understand this world one must try to understand the atoms that compose it.
- 5. The Elements Around 114 known elements and 92 are naturally occurring The term “element” can mean different things: Microscopic form Macroscopic form Elements comprised of molecules Diatomic molecules: Br I NClHOF
- 6. Symbols and Formulas Symbols for elements: Names are derived from Greek, Latin, and German Symbol is usually the first letter or first two letters of the element name. Rule: first letter is capitalized, second is not Formulas for compounds: Rules for writing formulas: Each atom present is represented by its element symbol. The number of each type of atom is indicated by a subscript written to the right of the element symbol. When only one atom of a given type is present, the subscript 1 is not written. hydrogen H nitrogen N boron B argon Ar calcium Ca nickel Ni silver Ag gold Au tungsten W copper Cu potassium K sodium Na lead Pb
Editor's Notes
- #2: 10/5/2007