AT Chemistry
2013
Chapter 2 Notes
Atoms, Molecules and Ions
Brief History Leading to Atomic View of Matter:
Aristotle:
Democritus:
Alchemy:
Robert Boyle: quantitative physical experiments ("The Skeptical Chemist")
Joseph Priestly: HgO(s)  Hg(l) + O2(g) (discovered oxygen – air cannot be an
“element”.
Henry Cavendish:
Zn + HCl(aq)  ZnCl2(aq) + H2(g) (discovered hydrogen)
FUNDAMENTAL CHEMICAL LAWS
* Law of Conservation of Mass (Laviosier)
MASS reactants = MASS products
In a combustion reaction, 46.0 g of ethanol reacts with 96.0 g of oxygen to
produce water and carbon dioxide. If 54.0 g of water is produced, how much carbon
dioxide is produced?
* Law of Definite Proportions (Proust)
A given compound always contains exactly the same proportion of elements by
weight. e.g. water = 11% H and 89% O by mass. Another way of saying this is that the
ratios of the masses of the elements in a compound are constant.
A sample of choloroform is found to contain 12.0 g of carbon, 106.4 g of chlorine,
and 1.01 g of hydrogen. If a second sample of chloroform is found to contain 30.0 g of
carbon, how many grams of chlorine and grams of hydrogen does it contain?
* Law of Multiple proportions (Dalton)
When two elements form a series of compounds, the ratio of the masses of the
second element that combine with 1 gram of the first element can always be reduced to
small whole numbers.
Mass of oxygen that combines
with 1 gram of tin
compound I
0.13 g SnO
compound II
0.26 g SnO2
Water, H2O, contains 2.02 g of hydrogen and 16.0 g of oxygen. Hydrogen
peroxide, H2O2, contains 2.02 g of hydrogen and 32.0 g oxygen. Show how these data
illustrate the law of multiple proportions.
Text problem 35
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Dalton's Atomic Theory (1808)
1.
Each element is made up of tiny indivisible particles called atoms.
2.
The atoms of a given element are identical; the atoms of different elements are
different in some fundamental way or ways.
3. Chemical compounds are formed when atoms combine with each other. A given
compound always has the same relative numbers and types of atoms.
4. Chemical reactions involve reorganization of atoms - changes in the way they are
bound together. The atoms themselves are not changed in a chemical reaction.
Law of Combining Volumes (Guy-Lusaac):
Under the same conditions of temperature and pressure, gases are found to react in
simple proportions by volume, and the volume of any gaseous products bears a wholenumber ratio to that of any gaseous reactant. Thus,
2 volumes hydrogen + 1 volume oxygen  2 volumes water
(at constant temperature and pressure)
3
Avogadro's Hypothesis:
At the same temperature and pressure, equal volumes of different gases contain
the same number of particles.
2 volumes hydrogen + 1 volume oxygen  2 volumes water
2 molecules hydrogen + 1 molecule oxygen  2 molecules water
Some Observations Experiments That Led to the Nuclear Model of the Atom
During the century that Dalton’s atomic model, evidence accumulated which indicated
that atoms had structure (i.e. an atom consisted of subatomic particles). What was this
evidence?
J.J. Thompson - classic experiment in which he subjected a cathode ray (a beam of
electrons exhibiting both wave and particle properties) to perpendicular electric and
magnetic fields inside an (almost) evacuated vessel.
Thompson realized that the amount of deflection is directly proportional to charge and
inversely proportional to mass; by adjusting the direction and strength of the magnetic
field, he caused the deflected beam to return to its original position. When this occurred
the force of electric field = force of magnetic field. He set the variables describing both
forces into an equation which had two unknowns: the charge and mass of the electron.
He solved for the charge to mass ratio:
Felectric = Fmagnetic
from this, e/m = 1.759 X 108 C/g
e = charge of electron
m = mass of electron
4
Robert Millikan - famous "oil-drop" experiment in determining the charge on the
electron. Millikan obtained a mist of very fine oil drops by spraying oil from an atomizer
in a chamber containing two electrically charged plates. Those oil drops that fell through
the hole of the positive plate were zapped with high energy waves (X-rays) which carry
enough energy to knock off the outermost electrons from the oil drops (i.e. to ionize
them). This leaves positively charged oil drops (which immediately descend to the
negative plate) and free electrons flying around. Now some of these electrons are
absorbed by other oil drops (in whole numbers of electrons) and these oil drops become
negatively charged. The negatively charged oil drops have two opposing forces acting
on them: the force of gravity pulling them down and the electric force on the negative
plate repelling them back up. If the electric charge on the plate is adjusted just so that the
charge remains suspended between the plates (as viewed through the eyepiece) then we
can say the two forces equal each other. Now using the variables representing these
forces and setting them equal to each other in an equation, Millikan was able to determine
the charge on the oil drops. He found this number to be 1.60 X 10-19 C (or some multiple
of 1.60 - representing two or more electrons on an oil drop).
Fweight = Felectric
Mxg = Ex e
e
mg
E
e = 1.60 X 10-19C
m = mass of oil drop
g = gravitational constant
E = charge on plates
e = charge on oil drop
5
Then from Thompson’s e/m ratio we can calculate the mass of an electron:
m = 1.60 X 10-19C/1.759 X 108C/g = 9.11 X 10-28 g
Thomson recognized that if atoms contained negatively charged electrons then they must
contain an equal amount of positive charge. Since the electrons made such a small mass
contribution, he speculated that the positive portion contributed not only most of the
mass, but also most of the volume of an atom. His model of the atom was a sphere of
positively charged matter in which tiny electrons were embedded (the “plum-pudding”
model). At the time, this was consistent with experimental evidence.
Ernst Rutherford – conducted an experiment that was expected to support Thomson’s
model. Alpha particles (or helium nuclei) are emitted by some radioactive substances.
When these alpha particles were allowed to strike a thin gold foil (only a few atoms
thick), most of the alpha particles passed through and a small percentage was deflected.
The degree of deflections was measured. The Thomson model, with its diffuse
distribution of positive charge, predicted that only small deflections of the positive, but
quite massive, alpha particle would occur. This is what was mostly observed, but once in
a while an alpha particle was deflected by a large angle (even 180o!). THIS was
incredible! Rutherford likened this behavior to a “15 inch shell fired at a piece of tissue
paper and bouncing back”. He concluded that something incredibly dense and positively
charged was present in the atom. Rutherford proposed that all of the positive charge and
most of the mass of an atom is concentrated within an extremely small central region
which he called the nucleus. This experiment became known as the classic "Gold-Foil"
experiment in which Rutherford proposed a nuclear model of the atom. (See schematic
next page). A valid size analogy would be comparing the size of a baseball (the nucleus)
ion the middle of Yankee stadium (the atom).
Rutherford was able to discover that the positive charge in a nucleus was due to a particle
that we call a proton. The proton has a charge equal in magnitude, but opposite in sign,
to the charge of an electron. The proton is approximately 2000 times more massive than
the electron, as one would expect from the properties of hydrogen. However, the helium
atom was known to possess only two electrons and two protons and the ratio of the
nuclear mass to electron mass (about 4000:1) was too high! This ratio was observed to
also be too high in atoms of other elements. The resolution of this difficulty was to
propose that there must be another massive, but uncharged, particle in the nucleus. This
particle, called the neutron, was not experimentally verified until the 1930’s due to the
difficulty of detecting an uncharged particle.
6
Conclusions:
1. atoms are mostly empty space - most alpha particles were not deflected
2. alpha particles deflected came close to a concentration of positive charge - the
nucleus
7
note: 1 atomic mass unit (amu) = 1.66 X 10-24 g
Modern Atomic Structure
A
X
Z
X = the element symbol
Z = atomic number = number of protons
A = mass number = number of protons plus neutrons
Fill in the following table:
Symbol
S2______
Cl-
Protons
Neutrons
Electrons
Charge
Mass
______
______
______
______
32.0
______
_____
______
_____
56
______
81
20
54
______
Text problems 53, 55, 59
8
NAMING COMPOUNDS
YOU MUST MEMORIZE the names and charges of the following ions:
1+
ammonium
cesium
copper(I)
potassium
silver
sodium
2+
NH4+
Cs+
Cu+
K+
Ag+
Na+
barium
beryllium
cadmium
calcium
cobalt(II)
copper(II)
iron(II)
lead(II) Pb2+
magnesium
mercury(I)
mercury(II)
nickel
strontium
zinc
1acetate
bromate
bromide
chlorate
chlorite
chloride
cyanide
fluoride
hydrogen carbonate
(bicarbonate)
hydrogen sulfate
hydroxide
iodide
iodate
nitrate
nitrite
permanganate
hydride
C2H3O2BrO3BrClO3ClO2ClCNFHCO3HSO4OHIIO3NO3NO2MnO4H-
Ba2+
Be2+
Cd2+
Ca2+
Co2+
Cu2+
Fe2+
3+
aluminum
chromium(III)
cobalt(III)
iron(III)
nickel(III)
Al3+
Cr3+
Co3+
Fe3+
Ni3+
Mg2+
Hg22+
Hg2+
Ni2+
Sr2+
Zn2+
2carbonate
chromate
dichromate
oxalate
oxide
peroxide
sulfate
sulfide
sulfite
tartrate
thiosulfate
CO32CrO42Cr2O72C2O42O2O22SO42S2SO32C4H4O62S2O32-
3phosphate
nitride
PO43N3-
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Symbol
Name
Symbol
Traditional
Stock
Co
cobalt
Co2+
Co3+
cobaltous
cobaltic
cobalt(II)
cobalt(III)
Cu
copper
Cu+
Cu2+
cuprous
cupric
copper(I)
copper(II)
Fe
iron
Fe2+
Fe3+
ferrous
ferric
iron(II)
iron(III)
Hg
mercury
Hg22+
Hg2+
mercurous
mercuric
mercury(I)
mercury(II)
Pb
lead
Pb2+
Pb4+
plumbous
plumbic
lead(II)
lead(IV)
Sn2+
stannous
tin(II)
4+
Sn
stannic
tin(IV)
-------------------------------------------------------------------------------------------------------1. Binary Salts
Sn
tin
A binary salt contains only one kind of cation (positive ion) and one kind of anion
(negative ion).
Cations fall into two general classes: elements that ionize to only one oxidation state and
those that can ionize to form several oxidation states (designated with roman numerals in
parentheses). The cation name is the name of the element plus the word "ion". In the
case of cations with multiple oxidation states the number of the oxidation state is
included.
The oxidation numbers for elements within the following groups is summarized:
Group 1 = +1
2 = +2
13 = +3
15 = -3 for N and -3 for P
16 = -2
17 = -1
Anions that are made up of a single element are named by replacing the suffix with "ide."
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The process of naming binary salts involves combining names which you separately
assign to the cation and anion halves. The only complication can be with determining
whether the cation requires a roman numeral. For those catoions that can have more than
one oxidation number we need to use Roman numerals top designate the charge on the
cation. Keep in mind:
a) The cation always comes first in a name
b) the total charge on a compound must equal zero.
example: calcium fluoride: __________
PbS2: ____________________
____________________
iron (III) chloride: _________
Hg2I2: ____________________
____________________
Text problems 63, 65
2. Ternary Salts (salts with polyatomic ions)
The same rules are followed when naming compounds involving polyatomic ions
as when naming binary salts. The only thing to keep in mind is that you don't change the
name of the polyatomic ion. In writing formulas, if you need to take the polyatomic ions
more than once to balance charge, you then write it in parentheses with the subscript
outside the parentheses.
Certain polyatomic anions contain different numbers of oxygen atoms combined with an
atom of a different element. These are called oxyanions. An oxyanion series normally
contains either 2 or 4 members. In a two member series, the anion with more oxygens
gets the suffix "ate," and the one with fewer oxygens gets the suffix "ite." When there are
4 atoms in the series, the sequence is:
IOIO2IO3IO4-
= hypoiodite
= iodite
= iodate
= periodate
Examples: NaBrO4 = ____________________
KIO3= ____________________
KMnO4 = ____________________
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3. Binary Covalent Compounds
Such compounds are formed between two nonmetals. These compounds can be
named using prefixes. Remember not to put mono in front of a single cation. The binary
covalent compound IF5, for example, could be named iodine pentafluoride. Using the
stock system we name it iodine(V) fluoride. Recall. 1 = mono, 2 = di, 3 = tri, 4 = tetra, 5
= penta, 6 = hexa, 7 = hepta, 8 = octa, 9 = nona, 10 = deca
traditional
stock
SO3
CO
N2O5
PCl3
Text problems 67, 71, 73, 75, 76
4. Acids
For now, we can define an acid as any substance containing hydrogen as the only
cation. To name an acid, determine if the anion contains oxygen (in which case it is
called an oxyanion). If the anion does not contain oxygen,
a. change the "ide" suffix to "ic acid,"
b. add the prefix "hydro" to the beginning of the name
For example, H2S is named hydrosulfuric acid. The one exception to the rule is CN(HCN is named hydrocyanic acid).
If the anion contain oxygen,
a. If the anion suffix is "ite," change it to "ous acid."
b. If the anion suffic is "ate,", change it to "ic acid."
Examples:
a) HF
____________________
b) HC2H3O2
____________________
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c) HBrO3
____________________
d) HBrO
____________________
e) HI
____________________
f) HNO2
_____________________
Additional Problems:
1. AlI3
____________________
2. Cd(HCO3)2
____________________
3. NaH
____________________
4. V2O5
____________________
5. P4O6
____________________
6. N2F4
____________________
7. SCl2
____________________
8. NaMnO4
____________________
9. Sn(IO3)4
____________________
10. (NH4)2C2O4
____________________
11. Sr(BrO3)2
____________________
12. Hg2I2
____________________
13. HgI2
____________________
14. HIO3
____________________
15. H2SO3
____________________
16. barium hydroxide
____________
13
17. sodium hypochlorite
____________
18. lithium peroxide
____________
19. calcium hydride
____________
20. plumbic acetate
____________
21. ferrous chromate
____________
22. nickel(III)oxide
____________
23. zinc sulfite
____________
24. periodic acid
____________
25. lead(IV)chloride
____________
26. potassium hydrogen sulfate
____________
27. gallium arsenide
____________
28. hydrofluoric acid
____________
29. silicon dioxide
____________
30. magnesium selenide
____________
Text problems 74, 77, 78, 80, 83, 85, 86
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