Atoms Flashcards
Greek atom
By Greek philosopher Democritus. Said, if you divided a mass again and again and again, you would end up with an indivisible particle, held together by hooks, called an atomos.
John Dalton
Developed an atomic theory: Atoms are tiny particles that make up elements; atoms can’t be divided; all atoms of a given element are the same; atoms of one element are different to all other elements. Developed first table of atomic masses
JJ Thompson
Discovered electron using cathode rays (emitted from cathode in cathode-ray tubes). Found cathode rays were a stream of particles with a negative charge, could be deflected by a magnetic and electric field and had a very very small mass. Concluded these particles came from the atoms in the electrode. Proposed plum pudding model.
Plum pudding model
Atom is a sea of positive charge, containing negatively charged particles
Ernest Rutherford
Proposed nuclear atom model. Geiger and Marsden fired alpha particles at gold foil and measured deflection. Found that they were deflected, disproving plum pudding model. From the deflections measured, Rutherford calculated an atom’s positive charge must be concentrated in the centre.
Neils Bohr and others
Proposed that electrons orbited nucleus in shells, otherwise they would spiral into the nucleus. Rutherford discovered the proton in 1918.
James Chadwick
Discovered the neutron when bombarding light elements with alpha particles.
Mass of an electron
1/2000 the mass of a proton
Isotope
Atoms of an element with different numbers of neutrons and different masses
Atomic (proton) number
Number of protons in the nucleus of an atom
Mass (nucleon) number
Number of particles (protons and neutrons) in the nucleus
Ion
Positively or negatively charged atom or (covalently bonded) group of atoms
Relative molecular mass or relative formula mass?
RMM for simple molecules; RFM for giant compounds
Standard measurement of relative masses
Carbon-12
Relative isotopic mass
Mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12
Relative atomic mass
The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12
RAM=
(sum of RIM x proportion)/total amount of stuff
Relative molecular mass
Weighted mean mass of a molecule unit compared with 1/12 of the mass of an atom of carbon-12
Relative formula mass
Weighted mean mass of a formula unit compared with 1/12 of the mass of an atom of carbon-12
