Powerpoint for Scientist Contributions and the Modern Theory

Powerpoint for Scientist Contributions and the Modern Theory of Atoms Mrs. Rigby Science 8

What is the smallest unit of matter? Can we see atoms? So, how do we know about them? Powers of 10 At what point can you no longer see the objects with your eyes? What tools would help magnify things?

Size of an atom: 0. 00000002 cm or 2 hundred millionth of a cm

Excuse me, how can you discover a particle so small that nobody has ever seen one?

Democritus Greek Philosopher 400 B C Atomos

Democritus • 460 BC - Greek philosopher proposes the existence of the atom • He pounded materials until he made them into smaller and smaller parts • He called them atoma which is Greek for “indivisible”.

Democritus • His Theory: All atoms: – Are small hard particles – Are made of a single material formed into different shapes and sizes – Are always moving, and they form different materials by joining together

John Dalton • 1803 - British chemist; elements combine in specific proportions to form compounds Solid Sphere Model

John Dalton • His Theory: § All substances are made of atoms that cannot be created, divided, or destroyed. § Atoms join with other atoms to make new substances. § Atoms of the same element are exactly alike, and atoms of different elements are different in mass and size.

Edward Frankland • 1852 - English chemist; developed the valence theory • His theory: – Every atom has a fixed number of bonds that it can form – For the atom to be stable, all of these bonds must be used

J. J. Thomson • 1897 - English chemist and physicist; discovered 1 st subatomic particles Plum Pudding Model or Raisin Bun Model Proposed by J. J. Thomson

J. J. Thomson • His Theory: – Atoms contain negatively charged particles called electrons and positively charged matter. – Created a model to describe the atom as a sphere filled with positive matter with negative particles mixed in – Referred to it as the plum pudding model

Ernest Rutherford • 1912 - New Zealand physicist discovered the nucleus Nuclear Model Proposed by Ernest Rutherford

Ernest Rutherford • His Theory: § Small, dense, positively charged particle present in nucleus called a proton § Electrons travel around the nucleus, but their exact places cannot be described.

Niels Bohr • 1913 - Danish physicist; discovered energy levels Bohr Model or Planetary Model Proposed by Niels Bohr

Niels Bohr • His Theory: § Electrons travel around the nucleus in definite paths and fixed distances. § Electrons can jump from one level to a path in another level.

Erwin Shrodinger • 1912 - Austrian physicist; developed the electron cloud model Electron Cloud Model Proposed by Erwin Schrodinger

Erwin Shrodinger • His Theory: § The exact path of electrons cannot be predicted. § The region referred to as the electron cloud, is an area where electrons can likely be found.

James Chadwick • 1924 - English physicist; discovered neutrons • His Theory: § Neutrons have no electrical charge. § Neutrons have a mass nearly equal to the mass of a proton. § Unit of measurement for subatomic particles is the atomic mass unit (amu).

Modern Theory of the Atom • Atoms are composed of three main subatomic particles: the electron, proton, and neutron. • Most of the mass of the atom is concentrated in the nucleus of the atom.

Modern Theory of the Atom • The protons and neutrons are located within the nucleus, while the electrons exist outside of the nucleus. • In stable atoms, the number of protons is equal to the number of electrons.

Modern Theory of the Atom • The type of atom is determined by the number of protons it has. • The number of protons in an atom is equal to the atomic number.

Modern Theory of the Atom • The sum of the number of protons and neutrons in a particular atom is called the atomic mass. • Valence electrons are the outermost electrons.