The Chemical Behavior of Atoms Day 1

Curriculum  Big Idea: Atomic theory is the foundation for the study of chemistry.  Concept: Energy is absorbed or emitted when electrons move from one energy level to another within the atom.  PA Standard: “Recognize discoveries from Dalton (atomic theory), Thomson (the electron), Rutherford (the nucleus), and Bohr (planetary model of atom), and understand how each discovery leads to modern theory. Describe Rutherford’s “gold foil” experiment that led to the discovery of the nuclear atom.”

Today’s Agenda 2/15/11  Opener: What is an electron?  Go over homework – in small groups and as a class.  Review of atomic theory as a class and Activity 4: Inquiring Further  Periodic Table: The Chemical Behavior of Atoms  (Periodic Table Activity 5 – See handout) 1. What Do You Think? 2. For You To Do 3. Powerpoint on Electrons  Closure Question Take Home Assignment: Read Chem Talk (pages , and answer the Checking Up Questions – p. 106 Quiz Thursday on Elements and Their Symbols – See Handout

Atom: the smallest particle of an element that retains its identity in a chemical reaction

Democritus  Among the first to suggest the existence of atoms  Believed that matter consisted of tiny, indivisible, unchangeable particles called atoms  His ideas did not explain chemical behavior and lacked experimental support

Dalton  Used experimental methods to transform Democritus’s ideas on atoms into a scientific theory.

Dalton’s Atomic Theory 1.All elements are compiled of tiny indivisible particles called atoms. 2.Atoms of the same element are identical. The atoms of any one element are different from those of any other element. 3.Atoms of different elements can physically mix together or can chemically combine in simple whole- number ratios to form compounds. 4.Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

Cathode Ray Tube Experiment  /cathode.html# /cathode.html#  Thompson found the charge to mass ratio of the electron to be constant, and concluded that electrons must be parts of the atoms of all elements.

Subatomic Particles Electrons  Negatively charged with very small mass  Located in orbitals, outside the nucleus  Discovered by J.J. Thompson  Cathode Ray Tube Experiment Protons and Neutrons… later

J. J. Thompson’s Plum Pudding Model

Rutherford’s Gold Foil Experiment

“This is almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”  The atom is mostly empty space.  The atom has a small, dense core where all of the positive charge is located.

Atomic Number  The whole numbers in the blocks of the periodic table  The number of protons in one atom of a given element  The number of electrons in a NEUTRAL atom of a given element  Every element has a different number of protons.

Protons, Neutrons, Electrons

The Bohr Model  Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.  Energy Levels: The fixed energies an electron can have  Quantum: The amount of energy required to move an electron from one energy level to another

The Quantum Mechanical Model  is based on mathematical equations developed by Erwin Schrodinger  determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.

Atomic Orbitals  regions of space in which there is a high probability of finding an electron

Closure Question How is light emitted from an atom?