History of Atom Ted Ed https://www.youtube.com/watch?v=xazQRcSCRaY Crash Course: https://www.youtube.com/watch?v=thnDxFdkzZs

The History of Atomic Theory The atom the smallest particle of an element that has the same the properties of the element Early ideas about matter Greek philosophers believed that matter was made of atomos that were the smallest pieces of matter. Aristotle believed matter was made of different combinations of earth, air, fire, and water. Alchemists experimented with matter and tried to turn common metals into gold. Their activities marked the beginning of our understanding of matter.

Democritus (460 BC) Greek philosopher believed everything was made up of TINY PARTICLES in empty space He called them Atomos, meaning “UNCUTTABLE”. He did not use experiments to support his ideas, just reason and logic. He pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called

Aristotle Philosopher Aristotle disagreed because he didn’t believe empty space could exist. Believed everything was made of 4 “Elements” Earth, Air, Water, Fire. Denial of existence of atoms persisted for 2000yr

First Concept of an Atom Democritus

1. all matter was made up of TINY SPHERES called ATOMS John Dalton 1766-1844 Suggested that: 1. all matter was made up of TINY SPHERES called ATOMS Introduced his ideas in 1803

John Dalton Developed Atomic Theory Atoms cannot be CREATED, DESTROYED, or DIVIDED into smaller particles. All atoms within the same element are IDENTICAL, but are different from atoms of other elements. Atoms combine in DEFINITE PROPORTINS to form Compounds. Considered the Father of Atomic Theory Introduced his ideas in 1803 John Dalton school teacher (1766 - 1844) developed a theory that was a new way of explaining matter. Conducted experiments He studied gases that make up Earth’s atmosphere. Based on his studies, he suggested that: matter is made of small, hard spheres that are different for different elements the smallest particle of an element is called an atom

Dalton’s Model

J.J. Thomson 1856-1940 1897 – Cathode Ray Experiment Discovered electron 1897 – Cathode Ray Experiment Discovered isotopes 1913

JJ Thomson’s Ideas

J. J. Thomson (1856 - 1940) Studied electric currents in gas discharge tubes (cathode ray tube) From his studies, he determined that the currents were streams of negatively charged particles. Discovered ELECTRONS JJ Thompson, British physicist who studied electrical current in cthode ray tubes Cathode rays were streams of negatively charged particles All substances produced these particles

J. J. Thomson (1856 - 1940) Proposed that atoms were made up of negatively charged particles scattered unevenly within a sphere surrounded by a positively charged matrix. Called it Plum Pudding or “RAISIN BUN” model JJ Thompson, British physicist who studied electrical current in cthode ray tubes Cathode rays were streams of negatively charged particles All substances produced these particles

Raisin Bun Model

Ernest Rutherford (1910) Gold Foil Experiement: Fired Helium nuclei at a piece of gold foil which was only a few atoms thick. Oversaw Geiger and Marsden carrying out his famous experiment.

Alpha Particle Experiment

Ernest Rutherford (1871 - 1937) Found that although most of them passed through, about 1/10,000 hit. He suggested that the deflection of the charged particles was because the atom contained a TINY DENSE CORE. Scientist from New Zealand Exposed thin sheet of gold to a stream of high speed particles with a positive charge, (alpha particles). The alpha particles cted like tiny bullets. Some particles went through and hit screen on other side., consistent with Thomson’s model (bullet through a muffin) but some rebounded from the foil like a ball bouncing off a wall. Discovered nucleus – tiny dense positively charged center of atom. According to him, all mass was in nuc

Atom is mostly EMPTY SPACE. Atoms contains a tiny dense NUCLEUS Ernest Rutherford 1871-1937 Atom is mostly EMPTY SPACE. Atoms contains a tiny dense NUCLEUS Atom’s MASS is mostly in the nucleus. Electrons circle around OUTSIDE central nucleus. Nucleus contains POSITIVE and NEUTRAL particles (later called protons and neutrons) Scientist from New Zealand Exposed thin sheet of gold to a stream of high speed particles with a positive charge, (alpha particles). The alpha particles cted like tiny bullets. Some particles went through and hit screen on other side., consistent with Thomson’s model (bullet through a muffin) but some rebounded from the foil like a ball bouncing off a wall. Discovered nucleus – tiny dense positively charged center of atom. According to him, all mass was in nuc

Rutherford Model

Niels Bohr (1885 - 1962) studied gaseous samples of atoms, which were made to glow by passing an electric current through them. Added that the electrons were in ORBITS. Proposed that electrons surround the nucleus in specific “ENERGY LEVELS” or “SHELLS.” Each orbit could only hold a SET NUMBER of electrons. Danish physicist, student in Rutherford’s lab, Each gas produced a characteristic spectrum of light as a result, called a line spectrum. Light emitted by the gases was a result of high-energy electrons releasing energy. But electrons of a given gas emitted light only of certain wavelengths.  energy levels gaseous samples of atoms, which were made to glow by passing an electric current through them. Utilized Planck’s Quantum Energy theory Worked on the Manhattan Project (US atomic bomb)

Bohr Model

James Chadwick 1932 James Chadwick bombarded beryllium atoms with alpha particles. An unknown radiation was produced.

James Chadwick 1932 Chadwick interpreted this radiation as being composed of particles with a NEUTRAL charge and the approximate MASS of a proton. This particle became known as the NEUTRON.

Chadwick Model

James Chadwick 1932 Neutrons help to reduce the repulsion between protons and stabilize the atom’s nucleus

Electrons are particles and waves at the same time Ernst Schrödinger 1887-1961 Werner Heisenberg 1901-1976 Quantum Mechanical Model 1926: Electrons are in probability zones called “ORBITALS”, not orbits and the location CANNOT be pinpointed Electrons are particles and waves at the same time Developed quantum numbers based on theories of Einstein and Planck

Orbitals

Electron Orbitals

History of Atom Crash Course: https://www.youtube.com/watch?v=thnDxFdkzZs

Homework ATOMIC HISTORY TIME LINE WORKBOOK P

Atomic Theory Continues to Develop According to Dalton’s theory, atoms were indivisible and indestructible. Then Thomson discovered the electron and Rutherford discovered the nucleus, which was later found to be made up of neutrons and protons. The atom was not indivisible at all: it was made up of even smaller particles –subatomic particles. Discoveries that some of these subatomic particles were made up of still smaller particles.

I. Early Ideas about Matter and Atoms Researcher Idea Model Ancient Greeks Atomos- smallest piece of matter (n/a)   John Dalton (1766-1844) particles are small hard spheres that are different for different elements J. J. Thomson (1856-1940) Atoms have smaller particles called electrons (= raisin bread model) Ernest Rutherford (1871-1937)  electrons move around the nucleus and the nucleus is made up of protons and neutrons Neils Bohr (1885-1962) Electrons circle the nucleus in predetermined shells Ancient Greeks: Democritus believed everything was made up of tiny particles in empty space. Atomos. Uncuttable. No proof, just theory Aristotle disagreed. Didn’t believe empty space could exist. Denial for 2000yr John Dalton school teacher (1766 - 1844) developed a theory that was a new way of explaining matter. Conducted experiements He studied gases that make up Earth’s atmosphere. Based on his studies, he suggested that: matter is made of small, hard spheres that are different for different elements the smallest particle of an element is called an atom