Early Models of the Atom (2.1) Flashcards
Which law did Antoine Lavoisier introduce?
Law of Conservation of Mass
Which law did Joseph Proust introduce?
Law of Definite Proportions
Which law did John Dalton introduce?
Law of Multiple Proportions
What were the 4 key points of Dalton’s atomic theory?
- Elements are made of atoms
- Atoms of a given element are identical; different elements have different atoms
- Compounds form when atoms join together; a given compound always has the same numbers and types of atoms
- Reactions involve the rearrangement of atoms (but don’t change the atoms themselves)
Who created the billiard ball model?
John Dalton
What is the charge-to-mass ratio of an electron?
charge on the electron (e) in coulombs (C) / mass in grams = -1.76 x 10⁸ C/g
Which model did J.J. Thompson create and how does it work?
Plum pudding model: entire atom is positively charged with negative electrons embedded in it
What did Ernest Rutherford conclude when he tested Thomson’s model?
The center of the atom must be positively charged and dense; used the term “protons” for the positively charged particles; most of the atom is empty space
Which model did Rutherford create and how does it work?
Nuclear atom model: an atom with a dense positive nucleus containing protons with electrons moving around the nucleus
Who suggested the existence of neutrons and why?
Rutherford; found that protons and electrons could only account for about half the mass of any atom
Who proved the existence of neutrons?
James Chadwick
Who first explained the idea of isotopes and what are they?
James Chadwick; atoms of the same element with different masses
Describe the nucleus
Very dense; contains nearly all of the atom’s mass
In standard atomic notation, what does each letter stand for?
A - the number of protons + neutrons (mass number)
Z - the number of protons (atomic number)
X - element symbol
What changes and what stays the same in isotopes?
The number of electrons and neutrons CAN change; the number of protons NEVER changes for any element
Describe how protons behave
Protons are tightly packed inside the nucleus - these particles repel each other
Describe how neutrons behave
Neutrons separate the protons reducing repulsion and stabilizing the nucleus
What force attracts protons and neutrons to each other?
Strong nuclear force
What is needed to make an atom stable?
The right balance of protons and neutrons
What happens when protons and neutrons are not properly balanced?
The nucleus becomes unstable and decays into a more stable nucleus
Define radioisotopes
Isotopes with unstable nuclei that decay into different (often more stable) isotopes
Define isotopic abundance
The percentage of a given isotope in a sample of an element
What is a mass spectrometer?
A measuring instrument used to determine the mass and abundance of isotopes
What do we call the data produced by mass spectrometers?
Mass spectrum
Define nuclear radiation
Energy or small particles emitted as an isotope decays
What are the 3 common types of nuclear radiation?
- Alpha particles
- Beta particles
- Gamma radiation
Define alpha particle
Same as He-4 atom (2 protons and 2 neutrons) with +2 charge; low energy - can be blocked by paper
Define beta particle
A negatively charged electron that can pass through paper but not metals
Define gamma radiation
High energy electromagnetic radiation; travels at speed of light and can penetrate most things except for lead
Define atomic mass unit
The mass of an element shown in the periodic table (atomic mass units, u); one atomic mass unit is equal to one twelfth the mass of a carbon-12 atom
How do you calculate average atomic mass?
Sum the known isotopes for an element multiplied by their percentage abundance
Define electromagnetic radiation
One of the many ways energy travels; travels at the speed of light through a vacuum
Define wavelength
The distance between peaks or troughs in a wave
What is frequency?
The number of waves (cycles) per second that pass a given point per second
Which wavelength radiation has the highest frequency?
Short-wavelength radiation
What’s the speed of light formula?
(wavelength in m)(frequency in Hz) = C (speed of light)
What did Max Planck discover about matter?
Matter could not absorb or emit any quantity of energy