Chapter 2 Flashcards
(52 cards)
The concept of atoms was first proposed by the Greek philosophers ____ and ____ in the fifth century BC
Leucippus and Democritus
____, a term derived from the Greek word for “indivisible”
atomos
Later, Aristotle and others believed that matter consisted of various combinations of the four “elements”— ____, ____, ____, and ____
fire, earth, air, and water
In 1807, English schoolteacher John Dalton proposed his ____ ____.
atomic theory
What are the five postulates of Dalton’s Atomic Theory?
- Matter is composed of exceedingly small particles called atoms. An atom is the smallest unit of an element that can participate in a chemical change.
- 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.
- Atoms of one element differ in properties from atoms of all other elements.
- A compound consists of atoms of two or more elements combined in a small, whole-number ratio. In a given compound, the number of atoms of each of its elements are always present in the same ratio.
- Atoms are neither created nor destroyed during a chemical change, but instead rearrange to yield a different type(s) of matter.
Dalton’s atomic theory provides a ____ ____ of the many ____ ____ of matter that you’ve learned about.
microscopic explanation . . . macroscopic properties
What law is this? If atoms are neither created nor destroyed during a chemical change, then the total mass of matter present when matter changes from one type to another will remain constant
the law of conservation of matter
What is the Law of definite proportions? Another name for it?
Who discovered it?
Law of definite proportions or the law of constant composition: All samples of a pure compound contain the same elements in the same proportion by mass.
(Illustrated by experiments performed by French chemist Joseph Proust.)
What is the law of multiple proportions?
The law of multiple proportions states that when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small, whole numbers.
Briefly describe J/J/ Thomson’s cathode ray tube experiments?
J.J. Thomson experimented with cathode ray tubes.
Cathode ray tube:
-A sealed glass tube from which almost all the air had been removed
-Contained two metal electrodes
-When a high voltage was applied across the electrodes, a visible beam called a cathode ray appeared between them.
Regardless of the metals used, this beam was always deflected toward the positive charge and away from the negative charge.
Thompson was able to calculate the charge-to-mass ratio of the cathode ray particles.
The cathode ray particles were much lighter than atoms.
These particles are negatively charged.
These particles are indistinguishable, regardless of the source material.
This cathode ray particle is what we now call an electron
What did J.J. Thomson’s experiment determine and electron was?
A negatively charged, subatomic particle with a mass more than one thousand times less than that of an atom
How did Millikan conclude the charge of an electron?
The charge of an oil drop was always a multiple of a specific charge, 1.6 × 10–19 C.
Millikan concluded that 1.6 × 10–19 C was the charge of a single electron.
Thompson already showed the charge to mass ratio of an electron to be 1.759 × 1011 C/kg.
What did Ernest Rutherford’s fold foil scattering experiment set-up and what did it demonstrate?
Aimed a beam of alpha particles (alpha particles) at a very thin piece of gold foil.
alpha particles are positively charged.
The scattering of these a particles was examined using a luminescent screen that would glow briefly when hit.
The volume occupied by an atom must consist of a large amount of empty space. (because of small amounts of deflection)
A small, relatively heavy, positively charged body, the nucleus, must be at the center of each atom. (because of small amounts of deflection)
The nucleus contains most of the atom’s mass.
Negatively charged electrons surround the nucleus.
The proton, a positively charged, subatomic particle is located in the nucleus.
What are isotopes?
Atoms of the same element that differ in mass
(Frederick Soddy of England. Noble Prize in 1921.)
What are neutrons?
Where are they found?
Neutrons: Uncharged, subatomic particles with a mass approximately the same as that of protons
(Discovered by James Chadwick in 1932.)
Neutrons are also found in the nucleus.
The ____ contains the majority of an atom’s mass.
____ and ____ are much heavier than ____.
____ occupy almost all of an atom’s volume.
Diameter of an atom ____ m
Diameter of a nucleus is ____________________ m
nucleus
Protons and neutrons . . . electrons
Electrons
10^-10
100,000 times smaller 10^-15
If an atom could be expanded to the size of a ____ ____, the nucleus would be the size of a single ____.
football stadium . . . blueberry
Atoms and subatomic particles are very small
Example: A carbon atom weighs less than _______ g
Electrons have a charge of less than ____C
2x10^-23
2x10^-19
Small units are needed
____ ____ ____ (____)
1 ____ = 1.6605 x 10^-24 g
Mass of a carbon-12 atom = 12 ____
Fundamental unit of charge (e)
e = 1.602 × 10–19 C
Small units are needed
Atomic mass unit (amu)
1 amu = 1.6605 x 10-24 g
Mass of a carbon-12 atom = 12 amu
Fundamental unit of charge (e)
e = 1.602 × 10–19 C
Proton mass and charge?
Proton
Mass = 1.0073 amu
Charge = +1
Neutron mass and charge?
Neutron
Mass = 1.0087 amu (slightly heavier than a proton)
Charge = 0
Electron mass and charge?
Electron
Mass = 0.00055 amu
Charge = –1
The number of protons in the nucleus of an atom is its ____ ____ (____).
Atomic number (Z)
What is atomic number?
The number of protons in the nucleus of an atom is its atomic number (Z).
This is the defining trait of an element: Its value determines the identity of the atom.
For example, any atom that contains six protons is the element carbon and has the atomic number 6, regardless of how many neutrons or electrons it may have.
