Unveiling Atoms: From the Ancient Greeks to Modern Models
Explore the evolution of atomic theory from Democritus to John Dalton and the discoveries of electrons and nucleus by J.J. Thomson and Ernest Rutherford. Learn about sub-atomic particles, atomic models, and important atomic properties like isotopes and the periodic table.
Unveiling Atoms: From the Ancient Greeks to Modern Models
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Presentation Transcript
How small is an atom? • http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/
Atoms vs. Hyle • Atom - the smallest particle of an element. It can exist alone, or combined with other atoms. • Atoms were first suggested by Democritus (Greek philosopher, 400B.C.). • People that supported Democritus view were called “Atomists”. • Aristotle(300B.C.) did not support the idea of atoms. He believed that all matter was a continuous substance called hyle. Hyle was composed of: earth, air, fire and water.
John Dalton….THE MAN! • John Dalton-(English school teacher) first to explain the existence of atoms and disspelling Aristotle’s theory of matter.
John Dalton • Formulates Atomic Theory: • Each element is made up of tiny indivisible particles called atoms. • The atoms of a given element are identical, atoms of different elements are different. • Chemical compounds are formed when atoms come together, in simple whole number ratios. • Chemical reactions involve the reorganization of the atoms; combined, separated or rearranged.
1903: J.J. THOMSON • Discovers the electron, using his famous Cathode Ray Tube (CRT), which turns out to be a primitive TV or computer monitor.
Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle, the electron. Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
1911 Ernest Rutherford • Rutherford discovers the nucleus of an atom, using his famous gold foil experiment.
Rutherford’s Gold Foil Experiment • Alpha () particles are helium nuclei • Particles were fired at a thin sheet of gold foil • Particle hits on the detecting screen (film) are recorded
Characteristics of sub-atomic particles Particle symbol charge location mass Proton p+ +1 nucleus 1 amu Neutron no 0 nucleus 1 amu Electron e- -1 orbital 1/1840 amu amu = atomic mass unit, unit used to mass very small objects. (1 amu = 1/12 the mass of a carbon-12 nucleus) Orbital – the 3-dimensional space around the nucleus of an atom, where electrons are found most of the time.
Atomic Models • JJ Thomson model(Plum pudding model) electrons are scattered throughout the atom, like raisins in plum pudding. • Rutherford Model-The atom has a central dense core, but is mostly empty space. • Bohr Model(Planetary model)Electrons orbit the nucleus in circular paths, called energy levels • Quantum Model (Modern, Shrodinger model)- Electrons move randomly in spaces called orbitals, around the nucleus.
Thomson’s Atomic Model Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.
Rutherford’s Findings • Most of the particles passed right through • A few particles were deflected • VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions: • The nucleus is small • The nucleus is dense • The nucleus is positively charged
The Bohr Model of the Atom I pictured electrons orbiting the nucleus much like planets orbiting the sun. But I was wrong! They’re more like bees around a hive. Neils Bohr
Quantum MechanicalModel of the Atom Mathematical laws can identify the regions outside of the nucleus where electrons are most likely to be found.
Important definitions about atoms: atomic number= number of protons in the nucleus of an atom. The number of protons determines the element of an atom. atomic mass number= mass of the atom in amu, it includes the number of protons and neutrons. (electrons are not counted) Isotopes = atoms of the same element, with a different number of neutrons in the nucleus. Isotopes of each element have the same atomic number, but different mass numbers.
Find the number of protons, neutrons and electrons in each: • Carbon-14 • Nitrogen-15 • U-235 • Hydrogen-3 • Carbon-13 • Helium-3 • B-11 • Cu-64
List the Element Family: Element FamilyElement Family Br Fe K U Sr Si Ce C Ar Cs
Orbital- the 3-d space around the nucleus of an atom where an electron is found most of the time. Each orbital can hold up to 2 electrons of opposite spin.
Orbitals have different shapes: Orbital shape s spherical p dumbbell d clover or dumbbell/donut f too complex
energy electron sublevels # of orbitals capacity s 1 2 p 3 6 d 5 10 f 7 14 g* 9 18 *orbitals exist, but not used most of the time. Energy sublevels around an atom
Aufbau Order- Energy levels & orbital types around the atom Aufbau order- Electrons fill orbitals closest to the nucleus first. • 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p,6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
Pre AP Chemistry: Nuclear Equations • Nuclear Reactions(transmutation reactions) are represented with Nuclear Equations. • Transmutation reactions – a reaction where one nucleus changes element. (# of protons)
Nuclear equations • See board
Half-life: the amount of time it takes for ½ of a sample to react or decay. • The half life of Ti-48 is 47 hrs. How much of a 250 gram sample remains after 94 hrs? • A 100gram sample of Cd-114 decays until only 12.5 grams remain in a total of 41years. What is the half-life for this isotope?
Electron orbitals • Orbital – a 3-dimensional space around the nucleus which can hold up to 2 electrons, with opposite spin. *electrons are found in their orbitals 99.9% of the time. Orbitals have different shapes: s, p, d, f
Orbitals have different shapes: Orbital shape s spherical p dumbbell d clover or dumbbell/donut f too complex
energy electron sublevels # of orbitals capacity s 1 2 p 3 6 d 5 10 f 7 14 g* 9 18 *orbitals exist, but not used most of the time. Energy sublevels around an atom
