Chapter 2 - Atoms, Molecules, & Ions Flashcards
-Describe Dalton's atomic theory -Describe the key experiments that led to the discovery of electrons & to the nuclear model of the atom -Describe the structure of the atom (proton, neutron, electron) -Describe the electric charge & relative masses of atomic particles -Use chemical symbols w/ atomic # & mass # to express the subatomic composition of isotopes -Understand atomic weights & how they relate to the masses of individual atoms & their natural abundances -Describe how elements are
2.1
Define “Dalton’s atomic theory”.
- Each element is composed of atoms.
- All atoms of a given element are identical in mass & other properties, but atoms of one element are different from the atoms of others.
- The atoms of one element cannot be changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.
- Compounds are formed when atoms of >1 element combine; a given compound always has the same relative # & kind of atoms.
2.1 - Give It Some Thought (p. 39)
1 compound of C & O contains 1.333g of O per gram of C, whereas a second compound contains 2.666g of O per gram of C.
(a) What chemical law do these data illustrate?
(b) If the 1st compound has an equal # of O & C atoms, what can we conclude about the composition of the 2nd compound.
(a) Law of multiple proportions
(b) The 2nd compound must contain 2 O atoms for each C atom
2.1
Define “Law of Constant Composition”.
In a given compound, the relative numbers and kinds of atoms are constant.
Basis of Dalton’s Postulate 4.
2.1
Define “Law of Conservation of Mass”.
The total mass of materials present after a chemical reaction is the same as the total mass present before the reaction.
Basis of Dalton’s Postulate 3.
–Atoms always retain their identities & that atoms taking part in a chemical reaction rearrange to give new chemical combinations.
2.1
Define “Law of Multiple Proportions”.
If 2 elements A + B combine to form >1 compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers.
There are compounds that use the same elements, but are not the same compound due to the amount.
Ex. H2O & H2O2
- H2O: 1.0g H + 8.0g O
- H2O2: 1.0g H + 16.0g O
Ex. CO & CO2 … small whole numbers
2.2
J.J. Thomson - 1897
- Experiment
- Discovery
- Model
- Cathode Ray experiment.
- Discovered electrons.
- Plum pudding model - + charged sphere with electrons scattered throughout
2.2
Robert Millikan - 1909
- Experiment
- Discovery
Measured the charge of an electron.
Small drops of oil, which had picked up extra electrons, were allowed to fall btwn. 2 electrically charged plates.
1. Millikan monitored the drops, measuring how the voltage on the plates affected their rate of fall.
- Charges were always integral multiples of 1.602 x 10^-19 Coulombs - the charge of a single electron.
Discovered mass by dividing charge by charge-to-mass ratio. Mass is 9.10 x 10^-28g.
2.2
Henri Becquerel - 1896
Discovered radioactivity while studying a U compound
2.2
Ernest Rutherford
1.Gold foil experiment. Aimed alpha particles at gold tin foil. Most went straight through, but some deflected. Postulated that mots of the mass of each Au atom in his foil & all of its + charge reside in a very small, extremely dense region- nucleus.
- Nucleus, Protons
Alpha, beta, gamma radiation
2.2
James Chadwick - 1932
Neutrons
2.3
Why do atoms lack a net electrical charge?
Every atom has an equal number of electrons & protons.
2.3 Give It Some Thought (p. 43)
(a) If atom has 15 protons, how many electrons does it have?
(b) Where do the protons reside in an atom?
(a) 15
(b) Nucleus
2.3 Sample Ex.
The diameter of a US penny is 19 mm. The diameter of an Ag atom is only 2.88 A. How many Ag atoms could be arranged side by side in a straight line across the diameter of a penny?
(19 mm)(10^-3 m / 1 mm)(1 A / 10^-10 m)(1 Ag atom / 2.88 A) = 6.6 x 10^7 Ag atp,s/
2.3 Practice Ex.
The diameter of a C atom is 1.54 A.
(a) Express this diameter in pm.
(b) How many C atoms could be aligned side by side in a straight line across the width of a pencil line that is .20 mm wide?
a. (1.54 A)(10^-10 m / 1 A)(10^12 pm / 1 m) = 154 pm
b. (.20 mm)(10^-3 m / 1 mm)(1 A / 10^-10 m)(1 C atom / 1.54 A) = 1.3 x 10^12 C atoms
In calc… .2xE^-3/E-10/1.54
2,3
Define “atomic number”.
The number of protons in the nucleus of an atom of any particular element.
2.3
Define “mass number”.
The total number of protons + neutrons in the atom.
2.3
Indicate 3 ways to write Carbon-12.
12C ; carbon-12; 12C
6
2.3
Define “isotope”.
Atoms with identical atomic numbers, but different mass numbers (same proton #, different neutron #).
2.3 - Samp. Ex.
How many P, N, & E are in
(a) 1 atom of 197 Au
(b) 1 atom of Sr-90
(a) 79 P, 79 E, 118 N
(b) 38 P, 38 E, 52 N
2.3 - Samp. Ex.
Mg has 3 isotopes, w/ mass numbers 24, 25, and 26.
(a) Write the complete chemical symbol for each of them.
(b) How many neutrons are in an atom of each isotope?
(a)
24Mg ; 25Mg ; 26Mg
12 12 12
(b)
12, 13, 24
2.4
1 amu = x g
1.66054 x 10^-24g
2.4
1g = x amu
6.02214 x 10^23 amu
- 4
- 93% C-12; 1.07% C-13
Find amu.
(.9893)(12) + (.0107)(13) = 12.01 amu
