Ch.2 Flashcards
(39 cards)
Who were the early philosophers that discussed the basic structure of matter?
Leucippus and Democritus
What term did Leucippus and Democritus use to describe the smallest particles of matter?
atomos
What did Aristotle believe about the composition of matter?
Matter consisted of various combinations of the four elements: fire, earth, air, and water
This view dominated for over two thousand years
Who revolutionized chemistry with atomic theory in the early 19th century?
John Dalton
(Dalton Postulate 1) What is the smallest unit of an element that can participate in a chemical change?
Atom
(Dalton Postulate 2) Fill in the blank: An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all _______.
atoms of that element
What does Dalton’s atomic theory state about compound’s ratios?
The number of atoms of each element are always present in the same ratio. Whole number ratio
What does Dalton’s atomic theory state (postulate 5) about atoms during a chemical change?
Atoms are neither created nor destroyed but are rearranged
What is the law of conservation of matter?
The total mass of matter remains constant during a chemical change
What does the law of definite proportions state?
All samples of a pure compound contain the same elements in the same proportion by mass
True or False: Samples that have the same mass ratio are necessarily the same substance.
False
Many compounds other than isooctane also have a carbon-to-hydrogen mass ratio of 5.33:1.00.
What is the law of multiple proportions?
When two elements react to form more than one compound, a fixed mass of one element reacts with masses of the other element in a ratio of small, whole numbers
What does this ratio demonstrate?
1.116 g Cl/1 g Cu – brown compound
(divided by)
0.558 g Cl/1 g Cu – green compound
= 2/1
The law of multiple proportions
The brown compound has twice the amount of chlorine per amount of copper as the green compound
What was physicist J.J. Thomson’s main experiment?
A cathode ray tube experiment investigating electrical discharges in low-pressure gases.
What did J.J. Thomson find in his cathode ray tube experiment?
Particles in the cathode ray were negatively charged, less massive than atoms, and fundamental subatomic constituents of all atoms. They are now called electrons.
What was Robert A. Millikan’s main experiment?
The oil drop experiment, where microscopic oil droplets were electrically charged and suspended using an electric field to determine the charge of a single electron.
How did Millikan’s experiment confirm the charge of an electron?
The charge of an oil droplet was always a multiple of 1.6 × 10⁻¹⁹ C, meaning it must be the fundamental charge of a single electron.
How was the mass of an electron determined?
Since Thomson had already found the charge-to-mass ratio (1.759 × 10¹¹ C/kg), and Millikan found the charge, the mass was calculated using a simple equation.
What was J.J. Thomson’s model of the atom?
The “plum pudding” model (1904), which described a positively charged mass with electrons embedded in it.
What was Ernest Rutherford’s experiment?
A beam of high-speed, positively charged alpha (α) particles was directed at a thin gold foil to observe how they scattered.
What surprising result did Rutherford observe in his experiment?
Most α particles passed through the foil, but some were slightly deflected, and a few bounced almost straight back.
How did Rutherford describe his unexpected findings?
He compared it to firing a 15-inch shell at a piece of tissue paper and having it bounce back.
What did Rutherford conclude about the volume of an atom?
Most of the atom consists of empty space.
What did Rutherford determine about the nucleus of an atom and why?
The nucleus is small, heavy, and positively charged because some α particles deflected sharply when they encountered its concentrated positive charge.