chem atom

Nuclear Model

-Ernest Rutherford -1911 -Rutherford fired positively charged alpha particles at a thin sheet of gold foil. Most passed through with little deflection, but some deflected at large angles. This was only possible if the atom was mostly empty space, with the positive charge concentrated in the centre: the nucleus. -Realized positive charge was localized in the nucleus of an atom -Do not explain why electrons remain in orbit around the nucleus

Quantum Model

-Erwin Schrodinger -1926 -Schrondinger stated that electrons do not move in set paths around the nucleus, but in waves. It is impossible to know the exact location of the electrons; instead, we have 'clouds of probability' called orbitals, in which we are more likely to find an electron. -Shows electrons didn't move around the nucleus in orbits, but in clouds where the position is uncertain -Still widely accepted as the most accurate model of the atom

Plum Pudding Model

-J.J. Thomson -1904 -Thomson discovered electrons (which he called 'corpuscles') in atoms in 1897, for which he won a Nobel Prize. He subsequently produced the 'plum pudding' model of the atom. It shows the atom as composed of electrons scattered throughout a spherical cloud of positive charge. -Recognized electrons as components of atoms -No nucleus: didn't explain later experimental observations

Solid Sphere Model

-John Dalton -1803 -Dalton drew upon the Ancient Greek idea of atoms (the word 'atom' comes from the Greek 'atomos' meaning indivisible) -His history stated that atoms are indivisible, those of a given element are identical and compounds are combinations of different types of atoms -Recognized atoms of a particular element differ from other elements -Atoms aren't indivisible - They're composed from subatomic particles

Planetary Model

-Niels Bohr -1913 -Bohr modified Rutherford's model of the atom by stating that electrons moved around the nucleus in orbits of fixed sizes and energies. Electron energy in this model was quantized; electrons could not occupy values of energy between the fixed energy levels. -Proposed stable electron orbits; explained the emission spectra of some elements -Moving electrons should emit energy and collapse into the nucleus, model did not work well for heavier atoms

wave mechanical model (Modern Atomic Theory)

1926 Small, dense, nucleus positively charged nucleus surrounded by electrons moving in "electron cloud." "Orbitals" are areas where an electron with a certain amount of energy is most likely to be found -In the current model of the atom, electrons occupy regions of space (orbitals) around the nucleus determined by their energies.

Thomson - development of the Plum Pudding Model

1st Experiment

Dalton Model/

Atoms as billard balls 1. atoms are tiny, invisible particles 2. atoms of one element are all the same 3. atoms of different elements are different 4. Compounds form by combining atoms Solid sphere model or bowling ball model Proposed by John Dalton

Dalton: model

Cannonball 1803 -Elements are made of atoms -Atoms of an element are the same -Atoms of different elements are different; (different masses) -Compounds are formed from combinations of atoms -Dalton proposes the indivisible unit of an element is the atom.

Rutherford's Model - Planetary/

Discovered Protons & The Nucleus Found out Atoms are mostly empty space! -Nucleus has all the positive charge. -Electrons orbit the nucleus. Rutherford accepted the electron's presence, but he didn't have a reason to see them from his experiments. The inward force that the electric charge of the nucleus exerts on the electron keeps it in a circular orbit.

JJ Thomson's Model - The Plum Pudding Model/

Discovered the electron Posited the existence of protons -its name is supposed to make you think of a lump of stuff with little pieces floating inside it. -This model of the atom is that small negatively charged electrons are floating around inside a lump of positively charged material. -positively charged "pudding" -electron "plum"

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Each atom is made of a positively charged nucleus with one or more orbiting, negatively charged electrons.

Rutherford

Experiment - Gold Foil 1911 -Bombarded gold foil with alpha particles. Showed atoms were mostly empty space with small, dense positively charged "nucleus" -These positive charged particles inside the nucleus are call protons -Rutherford demonstrates the existence of a positively charged nucleus that contains nearly all the mass of an atom.

Democritus

Greeks philosopher -Matter cannot be divided into smaller pieces forever

Democritus/

He proposed that matter could NOT be divided into smaller pieces forever Matter was made of small, hard particles that he called "atmos"

Bohr model

Planetary model 1913 -Small, dense, positively charged nucleus surrounded by electrons in circular orbits 2-8-8-18 -Bohr proposes fixed circular orbits around the nucleus for electrons.

Thomson model

Plum pudding model 1904 -Experiment -Cathode Ray Tube -An atom contains small, negative charged particle. The particle is called "electron" -Electrons are evenly distributed and embedded in atoms -Thomson discovers electrons, believed to reside within a sphere of uniform positive charge (the plum pudding model).

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Protons and neutrons are found in the nucleus.

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Protons have a positive charge, neutrons no charge, and electrons a negative charge.

Bohr Model/

Rutherford could not account for atomic stability Electrons are in shells, which represent different energy levels. Atoms have specific number of shells

Electron Cloud Model/

Since the 1920s we have found that -Bohr proposes fixed circular orbits around the nucleus for electrons. move in discrete clouds around the nucleus. Circumferences of orbits Electron standing waves on the electron orbits

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The modern model of the atom has evolved over a long period of time through the work of many scientists.