Atom and periodic table history Flashcards
Who first used the term atom?
Democritus - Greek philosopher
What term does ‘atom’ derive from and what is it’s meaning?
Atomos - meaning indivisible
What did Democritus’ ‘Theory of the Universe’ consist of?
- All matter consists of atoms, which are small bits of matter too small to be seen
- There is an empty space between atoms
- Atoms are solid and have no internal structure
- Each atom of a different substance is different in size, shape and weight
Who formally proposed atomic theory? When?
John Dalton - English chemist, physicist and meteorologist - 1804
What were the main points of Dalton’s atomic theory?
- Everything is composed of atoms, which are the indivisible building blocks of matter and cannot be destroyed.
- All atoms of an element are identical.
- The atoms of different elements vary in size and mass.
- Compounds are produced through different whole-number combinations of atoms.
- A chemical reaction results in the rearrangement of atoms in the reactant and product compounds.
What was Dalton’s atomic model?
While all atoms of an element were identical, different elements had atoms of differing size and mass.
Who is credited for discovering the electron? When?
J.J Thomson - English physicist - 1897
How did he discover the electron?
https://youtu.be/Rb6MguN0Uj4
What was his atomic model called and what did it consist of?
Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged “soup.”
What else did Thomson find?
- Electrons are in everything and 1000 times smaller than the smallest atom
- Positive item are missing electrons and negative items have too many electrons
- Current is the flow of electrons from negative to positive
Who discovered the nucleus? When?
Ernest Rutherford - New Zealand physicist - 1911
How did Rutherford discover the nucleus?
Rutherford aimed alpha particles at gold foil and recorded the location of the alpha particle “strikes” on a fluorescent screen as they passed through the foil. Most of the alpha particles went straight through but some were slightly deflected when they came close to the positively charged nucleus while some bounced back as they hit the nucleus head on.
When did Rutherford conduct the experiment? What is it called?
1909 - The alpha-scattering experiment
Who discovered the proton and when?
Ernest Rutherford - 1920
Who discovered the neutron? When?
James Chadwick - British physicist - 1932
