Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 3 Notes: Atoms and Moles Dalton’s Atomic Theory John Dalton (British Teacher) Composed in early 1800’s Mostly still true today 5 parts o All matter is composed of atoms o All atoms of the same element have identical properties o Atoms of different elements have different properties o Atoms of different elements combine in definite whole number ratios to form compounds o In chemical reactions, atoms are combined, separated, or rearranged but NEVER created or destroyed Law of Definite Proportions Compounds always contain the same elements in the same ratios o Water is always H2O, nothing else. o H2O2 exists but it is a different compound Law of Conservation of Mass Mass cannot be created or destroyed Reactants Products Law of Multiple Proportions It is possible to have 2 different compounds made from the same elements but just in different ratios For example CO2 (carbon dioxide) CO (carbon monoxide) Atomic Structure Atoms are composed of 3 basic subatomic particles Proton o Positively charged o Found in nucleus o p+ Neutron o No charge o Found in nucleus o n0 o same size as proton Electron o Negatively charged o Found in the electron cloud (surrounding nucleus) o e- o approximately 1800 times smaller than a p+ or n0 o discovered by JJ Thomson- cathode ray experiment Rutherford’s Experiment Ernest Rutherford Proved the existence of a small dense positively charged nucleus Originally thought atoms were solid; experiment ended up proving the opposite See diagram of Rutherford’s exp. in Chapter Atomic Number Represents the number of protons in the nucleus of an atom Unique number for each element Cannot be changed Mass Number Total number of protons and neutrons in the nucleus of an atom It can possibly change since the number of neutrons in an atom is subject to chance occasionally (isotopes) Atomic Models Theories of what we think the atom looks like These have changed over time Evidence is mostly indirect (wrapped present) 4 majors historic models o Thomson’s model Plum pudding Solid shell Electrons move around in positively charged pudding like material o Rutherford’s model Solid dense positive nucleus Electrons found on the outside (nothing specific about e-) Atoms consist mostly of empty space o Bohr’s model Just like Rutherford’s except Bohr believed that the electrons orbited the nucleus in set paths similar to the planets around the Sun o Quantum model Current model Only change is that we know electrons DO NOT follow an exact orbit like the planets However, electrons do stay at a set distance from the nucleus (energy levels, orbitals, etc) Electrons act as both particles and waves (dual nature) Electromagnetic Spectrum Range of wavelengths of EMR EMR- electromagnetic radiation Electrons thought to be behaving as waves NOT particles in EMR Characteristics of Waves Wavelength- length of wave before it repeats o All EMR travels at the speed of light (3 x 108 m/s) Frequency (v)- number of wavelengths that pass a certain point in space per unit of time o Hertz (Hz)- SI unit of frequency o Number of waves (cycles) which pass a given point in one second Electron Configuration in the Atom Ground state- electrons in their lowest possible energy level around the atom (normal) Excited state- electrons that have absorbed energy and jumped to a higher energy level (will eventually drop back to the ground state and release energy as a result) See diagram discussing sublevels, orbitals, orbital shape, and energy levels. Aufbau principle- electrons fill orbitals of lowest energy first Pauli exclusion principle- only 2 electrons fit in each orbital Hund’s rule- for sublevels that contain more than 1 orbital (p,d,f), each orbital must accept 1 electron before any orbital of equal energy receives a 2nd electron in same orbital o 2 electrons in the same orbital must have opposite spins WORK ON e- configuration problems Atomic Mass Weight of an individual atom Unit used is the amu (atomic mass unit) 1 amu= 1/12 the mass of a C-12 atom Protons and neutrons each have a mass of approximately 1amu Mass of electrons is so small to be negligible An amu is so small that we don’t have a tool to measure; therefore, a way to group atoms together had to be developed Mole (mol) SI unit used to discuss the number of atoms A mole is a group of atom 1 mol= 6.02 x 1023 particles Analogous to 1 dozen = 12 particles o 1 C atom = 12.011 amu o 1 mol C = 12.011 grams = 6.02 x 1023 C atoms o 6.02 x 1023 is known as Avogadro’s Number Do problems involving conversions between mass-moles-atoms pages 102103