Chemistry Chapter 14 Section 1
What is matter? Matter is anything that has mass and takes up space What is matter made of?? Atoms. All matter is made of atoms. Atoms are the building blocks of Matter
There is also an Atomic Theory Different discoveries made by different scientists led to today s atomic model. Contributors: -Greeks -Dalton -Crookes -JJ Thomson -Rutherford -Niels Bohr -Schrodinger ( not in the book)
First Thoughts Greeks- believed matter is made of tiny particles. Geeks named the tiny particles atom Atom = uncuttable in Greek now we know that the atom can be divided into smaller particles by nuclear reactions
**Science today and in the past Past no means to perform a lot of experiments Discoveries were based in discussions, observations and reasoning There were philosophers instead of actual scientists
**Science and Technology today Technology allows us to perform experiments and to develop and prove theories That is why knowledge in constantly evolving Technology gives us the tools to do Science
Understanding the structure of the atom The model of the atom changed over time Electrons (-) charge Protons (+) charge Neutrons have no charge
How is that the atomic model evolved from Dalton s model to today s model?
Dalton s Ideas early 19th century 1. Matter is made up of atoms - correct 2. Atoms can t be divided into smaller parts - wrong 3. All the atoms of an element are exactly alike almost correct - isotopes 4. Different elements are made of different atoms correct Element gold has only atoms of gold 5. His model: a hard sphere like a marble. ( fig. 3)
Crookes - brought some evidence of Dalton s ideas. Late 19th century Using a cathode ray tube without air Demonstrated the presence of particles in matter
Thomson experiment(1897) used the CRT to understand what were those particles Thomson understood that: The particles in the CRT have a (-) charge These particles are in all materials These particles were later called atoms
Thomson s conclusions and Atomic Model Atoms have (-) particles But matter is neutral, it is not negative *So the atom must have also + charges Thomson created a new Model of the atom with (+) and (-) particles The (+) particles are called protons
Rutherford s Experiments ( 1906) Scientists needed more evidence to support Thompson s model Rutherford discovered the nucleus and described a new model of the atom
How did he discover the nucleus? Rutherford s Experiment fired (+) particles at a thin sheet of gold.
Real Results: The deflected particles passed close to a + area: nucleus The repelled ones hit a positive area: nucleus The ones that passed ( majority) hit a area: electrons
Rutherford s Model The Nucleus Almost all of the mass of the atom and all of its positive charges are located in a small region at the center of the atom called the nucleus. The (+) particles were later called PROTONS
So far scientists knew that the atoms has: 1) A nucleus in the center with positive particles called protons 2) Tiny Negative particles called electrons that move around the nucleus 3) Almost all the mass of the atom is concentrated in the center
We still have to understand how the NEUTRON was discovered.
How was the Neutron discovered? 1) Atoms have electrons and protons 2) Electrons have very little mass, so.. 3) The mass of an atom should have been approximately equal to the mass of its protons, but.. 4) The mass of most atoms is at least twice as much as the mass of its protons. WHERE is the rest of the mass coming from?
There must be something else in the nucleus to account for the extra mass. This third particle, which was later call the neutron would have the same mass as a proton and be electrically neutral. It was difficult to find the neutron because the neutron has no charge
The model of the atom was revised : The central nucleus with protons and neutrons The electrons surrounding the nucleus moving in orbits.
Niels Bohr (1913) Today we know that: Electrons are in constant, unpredictable motion and can t be described by moving in an orbit. The model of the atom was revised again.
*Erwin Schrodinger Model or Electron Cloud Model ( 1926) current model Electrons travel in a region surrounding the nucleus, which is called the electron cloud. The electrons can be anywhere, most likely close to the nucleus, attracted by the + forces
You should know: The model of the atom as we know today The particles name, where they are in the atom and its charges ******In a neutral atom the number of protons and electrons are the same The importance of Technology in the development of Science