History Of The Atom Flashcards
What is an element?
It is a substance that cannot be broken down further into simpler substances.
What is an atom?
An atom is the smallest unit of an element, having the properties of that element
What is a compound?
A compound is a substance formed when two or more chemical elements are chemically bonded together.
What is a molecule?
A molecule is a particle made up of two or more atoms that are chemically bonded together.
John Dalton-Model and Year
1803
Solid Sphere Model
What was Dalton right about?
-Recognized atoms of a particular element differ from other elements
What was Dalton wrong about?
Atoms aren’t indivisible-they’re composed from subatomic particles
J.J. Thomson-Model and Year
Plum Pudding Model
1904
What did Thomson’s theory suggest?
- He discovered electrons
- His model shows the atom as composed of electrons scattered throughout a spherical cloud of positive charge.
Rutherford-Model and Year
Nuclear Model
1911
What was Thomson right about?
Recognized electrons as components of atoms
What was Thomson wrong about?
No, nucleus; didn’t explain later experimental observation
What was Rutherford’s experiment?
He fired positively charged alpha particles at a thin sheet of gold foil. Most passed through with little deflection but some deflected at large angles.
What was Rutherford wrong about?
Did not explain why electrons remain in orbit around the nucleus
What was Rutherford right about?
Realized positive charge was localized in the nucleus of an atom.
Bohr-Model and Year
Planetary Model
1913
What did Bohr modify?
He modified Rutherford’s model of the atom by stating that electrons moved around the nucleus in orbits of fixed sixes and energies. Electron energy was quantized.
What was Bohr right about?
Proposed stable electron orbits
What was Bohr wrong about?
Moving electrons should emit energy and collapse into the nucleus.
Erwin- Model and Year
Quantum Model
1926
What did Schrödinger suggest?
Erwin stated that electrons move around in set paths around the nucleus but rather in waves. Because it is impossible to know the exact location of an electron instead we have clouds of probability called orbitals.
What was Erwin right about?(2)
- Showed electrons don’t move around the nucleus in orbits, but in clouds where the position is uncertain.
- Still widely accepted as the most accurate model of an atom.
Name 4 important things regarding Dalton’s theory.
- All matter is made up of tiny indivisible particles called atoms
- All atoms of a given element are identical in mass and properties
- Atoms of different elements combine in simple whole number ratios to form chemical compounds
- In chemical reactions, atoms are combined, separated or rearranged
