Main Ideas The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800's. An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus. The number of protons and the mass number define the type of atom. Unstable atoms emit radiation to gain stability.
John Dalton revived the idea of the atom in the early 1800s based on numerous chemical reactions.
Dalton’s atomic theory easily explained conservation of mass in a reaction as the result of the combination, separation, or rearrangement of atoms.
Dalton’s Atomic Theory Even though some of the theory was incorrect, It provided the basis we have today for atomic theory. As is common with science, his theory has since been revised and additional information learned.
STM Scanning tunneling microscopy (STM) is the highest resolution imaging and nanofabrication technique available. It relies on quantum tunneling of electrons from a sharp metal tip to a conducting surface. The 71 Angstrom diameter "quantum corral" shown above was created and imaged with an ultra-high vacuum cryogenic STM. Each sharp peak in the circle is an iron atom resting on atomically flat copper
Gamma rays are high-energy radiation with no mass and are neutral and cannot, by themselves, result in the formation of a new atom.
Gamma rays account for most of the energy lost during radioactive decay.
Question ? A reaction that changes one element into another is called what? A. chemical reaction B. beta radiation C. nuclear reaction D. physical reaction
Question ? Why are radioactive elements rare in nature? A. They do no occur on Earth. B. Most have already decayed to a stable form. C. They take a long time to form. D. They are too hard to detect.
Chemical reactions involve changes in the electrons surrounding an atom. Nuclear reactions involve changes in the nucleus of an atom.
There are three types of radiation: alpha (charge of 2+), beta (charge of 1–), and gamma (no charge).
The neutron-to-proton ratio of an atom’s nucleus determines its stability.
Question? Whose work led to the modern atomic theory? A. Dalton B. Rutherford C. Einstein D. Aristotle
Question? Which particle is not found in the nucleus of an atom? A. neutron B. proton C. dust D. electron
Question? Two isotopes of an unknown element have the same number of: A. protons B. neutrons C. electrons D. both A and C
Question? Lithium has an atomic mass of 6.941 and two isotopes, one with 6 neutrons and one with 7 neutrons. Which isotope is more abundant? A. 6 Li B. 7 Li C. Both isotopes occur equally. D. unable to determine
Question? What happens when an element emits radioactive particles? A. It gains energy. B. It gains neutrons. C. It loses stability. D. It loses energy.
Question? What is the smallest particle of an element that still retains the properties of that element? A. proton B. atom C. electron D. neutron
Question? How many neutrons, protons, and electrons does 124 54 Xe have? A. 124 neutrons, 54 protons, 54 electrons B. 70 neutrons, 54 protons, 54 electrons C. 124 neutrons, 70 protons, 54 electrons D. 70 neutrons, 70 protons, 54 electrons
Question? The primary factor in determining an atom's stability is its ratio of neutrons to ____. A. protons B. electrons C. alpha particles D. isotopes
Question? What is the densest region of an atom? A. electron cloud B. nucleus C. isotopes D. atomic mass
Question? Why are electrons attracted to the cathode in a cathode ray tube? A. The cathode is more stable. B. The cathode has a positive charge. C. The cathode has a negative charge. D. The cathode has no charge.
CIM Table 4.3 Properties of Subatomic Particles Figure 4.12 Rutherford's Experiment Figure 4.14 Features of an Atom Figure 4.21 Types of Radiation
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