History Of The Atompre-ap

Greeks Atom • Greek philosophers Democritus, Aristotle, Leucippus, and Epicurus • The 4th century B.C. • Believed all matter is made up of atoms • Beliefs and ideas of their atom… – Everything was made up of tiny and indivisible bodies called atoms – They were different size, shape, and made up of different types of atoms

Greek Model

Geometric Shapes

First Modern Atomic Ideas • Law of Definite Proportions – A compound always contains the same elements in the same proportion by mass. (No matter what amount you analyze.) • Law of Multiple Proportions – If 2 (or more) elements can make more than one compound, then the compounds made always have mass ratios of small whole #s.

Dalton’s Atom • John Dalton (1766 – 1844) • Dalton discovered that matter is made up of atoms of different weights. • Dalton’s atomic theory led by his observations – All matter is made of atoms – Atoms of a certain element are identical/atoms of different elements are different (not quite true) – Atoms cannot be subdivided, created, or destroyed (not true) – Atoms combine in simple, whole # ratios to form compounds – In chemical reactions, atoms are rearranged

Dalton’s Model

Sphere – no subatomic particles

Thomson’s Atom • J.J. Thomson (1856 – 1940) • Discovered electrons in 1897. • Performed experiment on passing electric current through gas at low pressure using a cathode ray tube. • Concluded: – Electrons must be parts of the atoms of all elements.

Thomson’s Model Electrons

Rutherford’s Atom • • • •

Ernest Rutherford (1871 – 1937) Discovered the atom has a nucleus in 1911 Tested his theory using a thin sheet of gold foil. Concluded: – An atom is mostly empty space – All the positive charge of an atom is concentrated in a small region called the nucleus. – The nucleus is composed of protons and neutrons. – Nearly all mass of an atom is in its nucleus

Gold Foil Experiment

Rutherford’s Model

Nucleus

Electrons

Bohr’s Atom • Neils Bohr (1885-1962) • Student of Rutherford • Concluded: – Proposed electrons are arranged in concentric circular paths, or orbits, around the nucleus. – Electrons in a particular path have a fixed energy – Energy levels of an electron is where the electron is likely to be moving.

Bohr’s Model

Quantum Mechanical Atom • Erwin Schrodinger (1887 – 1961) • Used a mathematical equation to describe the location and energy of an electron in a hydrogen atom. • Does not define a direct path an electron takes around the nucleus.

Quantum Mechanical Model

Electron Cloud

Atoms • Atom – the smallest particle of an element that retains the properties of that element. • Overall, typical atoms have no charge (# protons = # electrons). • Short range nuclear forces hold the nucleus together (proton-proton, proton-neutron, neutron-neutron)

Subatomic particles • Nucleus – center of atoms, contains neutrons and protons. • Neutron – a subatomic particle with no charge found in the nucleus of an atom. – Mass of 1 amu or 1.7 X 10 -27 kg

• Proton – a positively charged subatomic particle found in the nucleus of an atom.

• Mass of 1 amu or 1.7 X 10 -27 kg • Electron – a negatively charged subatomic particle. – Tiny mass (0.00055 amu or 9.1 X 10-31 kg)

The Atom

Trivia! If you were to spell out numbers, how far would you have to go until you would find the letter "A"?

One thousand