Ancient and modern scientists have significantly contributed to our understanding of the fundamental nature of matter and the forces governing it. Kanada, an ancient Indian philosopher, proposed that everything is composed of indivisible particles called '
Mosley's Perodioc Law
- In 1914, Mosley was able to determine the atomic number ( number of protons) of all the known elements.
- He rearranged the elements by increasing atomic number.
The Periodic Law was restated:
"As the generalization that there is that there is a recurring pattern in the proporties of the elements when arranged in order of occuring atomic number
The Strong Nuclear Force
How are the Positively Charged Subatomic Particles (Protons) Held Together in the Nucleus?
Ernest Rutherford's Posulates (based on the gold foil experiment);
- The atom is mostly empty space
- There is a dense middle that is positively charged
- The positive and negative charges exist separately
- It carries most of the atom's mass
The Gold Foil Expirement
- A beam of Alpha Particles was shot through a gold foil
- Most went straight through, although some were deflected
There must be positive subatomic particles to counteract the electrons.
What else are Atoms Composed of?
Invention of the Mass Specrometer by Francis Aston
Confirmed the existence of the first subatomic particle, the electron.
Robert Millikan
- Found the charge of an electron by doing an oil drop experiment
J.J. Thomson (1856- 1940)
- He deduced that cathode rays are composed of a single, negatively-charged particle that has a constant charge to mass ratio using CRT.
R q/m = constant
- He theorized that this is what all chemical elements are composed of.
Wilhelm Röntgen (1845- 1923)
- Discovered X-rays (a form of elctromagentic radiation) through vaccum tube expirements
Vacuum Tubes & Electricity
- Geissler Tubes and Crook's Tubes helped discover cathode rays.
- They also showed that cathode rays have mass.
Hans Christians Örsted (1777- 1851)
In 1820, he performed an experiment that showed there was a connection between electricity and magnetism.
Örsted's principle states that an when a steady electric field passes through a wire, it created a magnetic field around it.
Dmitri Mendeleev (1834-1907)
- In the 1870s, he organized the known elements into a chart according to thier atomic mass.
The first perodioc law stated, "the properties of the elements are a periodic function of thier atomic masses"
- Found a pattern between the elements and realized, logically, there must be missing, undiscovered elements.
Basic Laws of Chemistry After The 1700s
- Law of Conservation of Mass
- Law of Constant Composition
John Dalton (1766-1844)
In 1804, he bought back the ideas theorized by the Greek Philosophers and tested them using science.
He postulated:
- Matter is made up of fundamental particles
- These particles are invisible and indestructible
- They have a unique mass and fixed valences
- They are the units of chemical change
He also discovered the Law of Multiple Proportions
Empirical
Theoretical
Created Atomism (the idea that the word is made up of small, invisible things called atoms.)
How Can We Test This?
The Ancient Greek Atomic Theory
Leucippus (Early 5th century BCE)
He proposed that:
- Everything is made of two things, atoms and the void (empty space)
- They are infinite
- Atoms are indivisible, indestructible and join to form objects
- Without the void, there would be no motion
Democritus (460 BCE)
- Leucippus's Pupil
He proposed that:
- Atoms were specific to the objects they formed
- Atoms were different in sizs and shape
- Atoms were in constant motion in a void, and, if they collidided, they'd stick together or rebound. He believed this caused changes in mattet.
What are Objects Made Up Of?
Epicurus (341- 270 BCE)
He:
- Attributted mass to these particles
- Proposed that there are two types of motion, the motion of atoms and the motions of visible objects
- Proposed the idea of atomic 'swerve' (the idea that atoms swereve randomly, which is what provides free will.)
Asclepaides (~100 BCE)
-He considered atoms capable of forming clusters
Kanada (~ 600 BCE)
- Born in India
He proposed that:
- Objects can be broken down to a fundamental essence (he called it 'parmanu')
- Paramanu cannot be divided and are eternal.
- He said that parmanu are either in a state of motion or absolutely still
