Chapter 2 Flashcards
How did Leucippus, Democritus, and Aristotle conceptualize atoms?
According to Leucippus and Democritus the world is made up of two fundamental elements, atoms and the void. They believed atoms to be the smallest unit of matter, thus making them indivisible. In their model, atoms make up all physical objects and are uniform. Aristotle famously rejected atomism in On Generation and Corruption.
What are the postulates of Dalton’s Atomic Theory?
A theory of chemical combination, first stated by John Dalton in 1803. It involves the following postulates: (1) Elements consist of indivisible small particles (atoms). (2) All atoms of the same element are identical; different elements have different types of atom. (3) Atoms can neither be created nor destroyed.
How is Dalton’s Atomic Theory consistent with the Law of Conservation of Mass?
That mass can neither be created nor be destroyed.
What does the Law of Definite Proportions tell us?
The law of definite proportions states that a given chemical compound always contains the same elements in the exact same proportions by mass.
What does the Law of Multiple Proportions tell us?
The law of multiple proportions states that whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.
What did Thomson discover with the results of his cathode ray experiments?
Thomson’s experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons.
What information came from Millikan’s oil drop experiment?
The oil drop experiment allowed Millikan to determine the charge on the electron. He later used this data to determine the mass of the electron.
What were the features of the atom models proposed by JJ Thomson and Hantaro Nagaoka?
Thomson, a British scientist, discovers the electron. The later leads to his “plum-pudding” model. He pictures electrons embedded in a sphere of positive electrical charge. Hantaro Nagaoka, a Japanese physicist, suggests that an atom has a central nucleus.
What were the results of Rutherford’s gold foil experiments, and how did this disprove earlier models of the atom?
Rutherford’s gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus. Based on these results, Rutherford proposed the nuclear model of the atom.
What model did Rutherford propose based on his experiments?
Based on these results, Rutherford proposed the nuclear model of the atom.
What discovery did Frederick Soddy make about the masses of elements?
In 1913, he was the first to announce the concept that atoms can be identical chemically and yet have different atomic weights.
How did Chadwick account for the non-proton mass in the nucleus?
Using the kinetic energy and momentum of emitted protons, Chadwick showed that the mass of a neutron is slightly greater than that of a proton.
What are the charges and relative sizes of the different subatomic particles?
The size of the charges is the same, but the sign is opposite. Protons have a charge of +1, neutrons have a charge of 0, and electrons have a charge of -1.
How is an atomic mass unit (amu) defined?
AMU is defined as one-twelfth the mass of an atom of carbon-12 (12C). 12. C is the most abundant natural carbon isotope, accounting for over 98% of carbon found in nature. It has an AMU of 12.
What property defines what element an atom is?
The number of protons in the nucleus determines which element an atom is, while the number of electrons surrounding the nucleus determines which kind of reactions the atom will undergo.
