Chem Unit II Flashcards
Explain Democritus’ earliest ideas about the atom:
Democritus believed the atom is invisible, and is the smallest unit of matter in the universe which could not be divided.
Explain the five postulates of Dalton’s Atomic Theory and identify those that were later disproved:
Matter is composed of tiny particles called atoms ✓
Atoms are indivisible and indestructible. In a reaction, they are combined or rearranged but never broken apart ✕ (protons, neutrons and electrons make up atom, therefore atoms are divisible and can be broken apart)
Atoms of a given element are identical in size, mass and chemical properties ✕ (isotopes contain different amounts of neutrons from each other, making the mass and size of the atoms of same elements (isotopes) different)
Atoms of one elements are different from those of another element ✓
Different atoms combine in simple, whole number ratios to form compounds ✓
Identify the major contributions of key scientists to the development of modern atomic theory, and be able to explain the experiments which led them to their conclusions:
Thompson – The Electron, Cathode Ray Tube:
Experiment: Add an electric field and measure the deflection of particles.
Conclusion: The negatively charged particles are electrons, and atoms are not indivisible.
Millikan – Electron Charge, Oil Drop Experiment:
Experiment: Drops of oil are ionized (made to have a charge) and the voltage is varied until the oil drop is perfectly suspended in space.
Conclusion: Determined the mass and charge of the electron.
Rutherford – The Nucleus, Gold Foil Experiment:
Experiment: Gold Foil Experiment – alpha particles (positively charged radioactive particles) emitted at a sheet of gold foil just a few atoms thick.
Conclusion: The atom is made up of mostly empty space and has a small, dense nucleus of positive charge (protons).
Distinguish between the billiard ball, plum pudding and nuclear models of the atom:
Billiard Ball: Depicted the atom as simply an indestructible solid sphere.
Plum Pudding: Depicted the atom as a circular disc which had electrons sporadically placed throughout.
Nuclear Model: Depicted the atom as a circle containing numerous small electrons revolving around a small, dense nucleus with positive charge (protons).
Define what an atom is and distinguish between subatomic particles: protons, neutrons and electrons with respect to mass, charge and location in the atom:
Atom: Smallest form of matter that retains the element’s properties.
proton
- 1.673*10^-24 amu
- positive (+)
- nucleus
nucleus
- 1.675*10^-24 amu
- neutral (o)
- nucleus
electron
- 9.11*10^-28 amu
- negative (-)
- space around nucleus
Define atomic number, mass number, atomic mass and charge and be able to identify each on an elemental symbol or periodic table: ✓
Atomic number: The number of protons in an element which can determine the identity of an element.
Mass number: The total number of protons and neutrons in the nucleus of an atom (whole #).
Atomic mass: The weighted average mass of the isotopes of an element.
Charge: The number of protons versus the number of electrons in an atom.
Explain the role of atomic number in determining the identity of an element:
The atomic number represents the number of protons an element has. Since the specific number of protons for each element will never change, the atomic number is a good indication of the identity of an element.
Define isotope:
Atoms of the same element with different numbers of neutrons.
Distinguish between alpha, beta and gamma radiation and compare them with respect to composition, mass, energy, charge and penetrating power:
alpha
- 24He2+
4 amu
2+
paper
beta
-1 0e-
0 amu
1-
aluminum
gamma
energy, photons
00Ɣ
Ɣ
0 amu
0
lead
