Chemistry Unit 2 Quiz Review

Democritus

Greek philosopher who supported the particle theory of matter, made the term atomos, his ideas were challenged by other philosophers, including Aristotle and Plato

Atomos

invisible

Atom

the smallest particle of an element that retains its identity in a chemical reaction

John Dalton Model

Solid Sphere Model

Dalton proposed

• all matter is made up of indivisible atoms

• atoms of a given element are identical in size, mass, and properties

• atoms combine in simple whole-number ratios to form compounds

• atoms are combined, separated, or rearranged in chemical reactions

Dalton’s atomic theory (postulates of modern atomic theory)

• elements are made of tiny particles called atoms

• all atoms of the same element are considered identical (modern science has shown this is not completely true because of isotopes)

• atoms of one element are different from those of any other element

• atoms of one element combine with atoms of other elements to form chemical compounds

• Atoms are changed during chemical reactions, but they are never created or destroyed (Dalton wasn’t referring to nuclear reactions)

J.J. Thomson Model

Plum Pudding Model

Thomson’s experiment

Cathode ray tube

Thomson’s proposal

• atoms was a uniform, positively charged sphere with negative electrons embedded throughout (atoms contain both positive and negative charges)

Robert Millikan experiment

Oil drip experiment

Millikan proposed

• electrons are present in atoms of all elements

• atoms must contain a positive charge to balance the negative electrons

• He calculated the charge and the mass of an electron

Ernest Rutherford model

Nuclear model

Rutherford experiment

Gold foil experiment

Rutherford experiment conclusion

• most particles passed through undeflected

• some particles were deflected slightly

• some were deflected at large angles

• some particles even bounced directly back

Rutherford proposal

• much of the volume of an atom is empty space

• a densely packed, positively charged core contains most of the atom’s mass

• this central core is called the nucleus

Nucleus

the central core of an tom, composed of protons and later discovered neutrons

Niels Bohr model

Planetary model

Bohr proposed

• orbit the nucleus at fixed energy levels

• have higher energy when they are farther from the nucleus

• require more energy to move farther away from the nucleus

• When electrons return to a lower energy level, they emit energy in the form of light

• (problem with his model: model only works for the hydrogen atom)

Erwin Schrodinger model

Quantum model (also known as the wave mechanical model)

Schrodinger proposal

• developed and solved a mathematical equation to describe electrons in atoms

• his equation gives the energies an electron can have, which are called energy levels

• electrons are found in an area of probability called an orbitals

Heisenberg Uncertainty principle

states that the position and velocity of an electron cannot be determined

James Chadwick discovery

Discovery of the Neutron

Chadwick concluded

• he bombarded beryllium with alpha particles, which produced radiation that was electrically neutrally charged radiation

• radiation came from a new particle, which he called the neutron

• he also showed that the neutron is located in the nucleus

Solid Sphere model

• matter is made up of atoms

• atoms are considered discrete units

Plum Pudding model

• atoms have positive parts and negative parts

Nuclear model

• positive parts of the atom is located in the center (nucleus)

• this led to the discovery of the nucleus

Planetary model

• electrons orbit around the nucleus

• electrons occupy specific energy levels

Quantum model

• electrons move in complicated paths called orbitals rather than simple circular orbits

Proton (p+)

• positive

• about equal to a neutron (~1 amu)

Neutron (n0)

• neutral

• slightly greater than a positive charge (~1 amu)

Electron (e-)

• negative

• negligible (~0.0005 amu)