Chem 121 Exam 1 Flashcards
Democritus (What was he known for?)
Democritus (around 450BC) was one of the first to suggest that matter consisted of small invisible particles called Atomos
Aristotle (What was he known for?)
Aristotle suggested that matter was indefinitely divisible
John Dalton (What is he known for?)
John Dalton (1808) published an atomic theory which included
1. An element is composed of extremely small invisible particles called atoms
2. All atoms of a given element have identical properties, which differ from those of other elements
4. Compounds are formed when atoms of different elements combine with each other in small whole number ratios
5. The number and kinds of atoms are consistent in a given compound
Antione Lavoisier (What was he known for?)
- Atoms cannot be created, destroyed or transformed into atoms of other elements
i. Dalton is not credited with this it was Antione Lavoisier
Benjamin Franklin (What did he discover?)
Benjamin Franklin was the first to designate charges as positive and negative
Humphry Davy’s (What is he known for?)
Humphry Davy’s experiments in the 1800’s showed that when electric current was passed through some substances they decomposed (electrolysis). Davy proposed that the elements n compounds were held together by electrical forces.
Michael Faraday (What did he Discover?)
Michael Faraday’s experiments in 1832-1833. Faraday, one of Davy’s students determined the quantitative relationship between the electricity used in electrolysis and the extent to which the chemical reaction occurred
Henri Becquerel (What did he discover?)
The discovery of radioactivity by Henri Becquerel in 1896. Becquerel discovered that uranium would darken a photographic plate even in the absence of light. Marie and Pierre Curie worked with Becquerel on identifying radioactive substances
Ernest Rutherford (What did he Discover?)
Ernest Rutherford characterized three types of radiation
- He invented the nuclear model of the atom
- Alpha radiation was found to have a relative charge of +2 and a relatively large mass
- Beta radiation was found to have a relative charge of -1 and a relatively small mass
- Gamma radiation has no detectable charge or mass
J.J. Thompson (What did he discover?)
J.J. Thompson in 1897 studied the deflection of the cathode rays as a function of the strength of the applied electric and magnetic fields
- He invented the plum pudding model of the atom
- He used the results to calculate the charge (e) to mass (M) ratio of the electron
- The ratio was the same regardless of the nature of the gas in the tube the composition of the electrodes or the nature of the electric power source
- This indicates that the elections are fundamental particles present in all matter
Robert Millikan (What did he discover?)
Robert Millikan in 1909 designed an experiment to determine the fundamental charge of the electron
- His experiment is known as the oil-drop experiment
Tiny spherical oil droplets were produced an atomizer
H.G.J. Moseley (What did he discover?)
- In 1913 H.G.J. Moseley studied the x-rays given off by different elements
- Moseley correlated the wavelengths of the emitted x-rays with the number of the protons and developed the concept of the atomic number
- The atomic number is the number of protons in the nucleus determines the identity of the element
- For neutral atoms the number of protons is equal to the number of electrons
- For neutral atoms the number of protons is equal to the number of electrons
James Chadwick (What did he discover?)
The neutron was discovered in 1932 by James Chadwick who discovered that neutrons were produced when BE was bombarded by high-energy alpha particles
Isotopes (Definition)
Isotopes = atoms of the same element with the same atomic numbers and different mass numbers. They have the same numbers of protons but different numbers of neutrons
Number of neutrons (How to calculate neutrons?)
Number of neutrons = mass number - atomic number
