Chapter 4 review
Whose work is credited with being the beginning of the modern atomic theory? Distinguish between the ancient ideas and modern ideas of an atom. John Dalton Ancient: atoms were indivisible, solid piece of matter Modern: subatomic particles, can be divided
State the main points of Dalton’s atomic theory. All matter is composed of atoms Atoms of an element are identical Atoms cannot be subdivided, created or destroyed Atoms combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged
Define matter and give 2 examples Term for substance Ex. Pen, paper, book, elements, etc What is found in the nucleus of an atom? Neutrons, protons What is the charge of the nucleus Positive (because of the protons)
Who developed the “plum pudding” model of the atom? J.J. Thompson Describe the positive charge distributed in the plum pudding model. Evenly distributed throughout atom “positively charged pudding”
Explain why atoms are electrically neutral. Arrange the subatomic particles in order of increasing mass: neutron, electron, proton Electron is smallest, neutron is largest Explain why atoms are electrically neutral. The number of protons = number of electrons Which particles account for most of an atom’s mass? Protons and neutrons – they are the largest subatomic particles
Which subatomic particle was discovered by researchers working with cathode-ray tubes? Electrons What happened to the cathode-ray stream when a negatively charged plate was beside the tube? The stream moved away from the negatively charged plate
What kind of particles were used in the gold foil experiment? What caused the deflection of the alpha particles in Rutherford's gold foil experiment? The nucleus, which is very dense What kind of particles were used in the gold foil experiment? Alpha particles
How is an atom’s atomic number related to its number of protons How is an atom’s atomic number related to its number of protons? To electrons? How do isotopes differ? How are they similar? How is the mass number related to the number of protons and neutrons an atom has? Atomic number = # protons, # electrons Different # of neutrons, same # protons Mass number = # protons + neutrons
Define atomic mass unit. What are the benefits of developing the atomic mass unit as a standard unit of mass? Does the existence of isotopes contradict part of Dalton’s original atomic theory? Explain. Standard unit for subatomic particle Easier to work with compared to grams Yes – Dalton’s theory stated that atoms were identical in mass
Magnesium has 3 isotopes. Calculate its average atomic mass. Exact weight % abundance Mg – 24 23.99 amu 79% 23.99 x 0.79 = 18.95 amu Mg – 25 24.99 amu 10% 24.99 x 0.10 = 2.499 amu Mg – 26 25.99 amu 11% 25.99 x 0.11 = 2.859 amu 18.95 + 2.499 + 2.859 = 24.31 amu
Silver has 2 isotopes. Ag-107 has a percent abundance of 52% and Ag-109 has a percent abundance of 48%. What is the average atomic mass? Exact weight % abundance Ag – 107 107 amu 52% 107 x 0.52 = 55.64 amu Ag – 109 109 amu 48% 109 x 0.48 = 52.32 amu 55.64 + 52.32 = 107.96 amu