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Chemistry
CH 3 Tutorial
Chemical Reactions
Reactants  Products
Laws
1.
2.
3.
Law of conservation of Mass-mass is neither created or destroyed during chemical reactions
Mass of reactants = Mass of products
Law of Definite Proportions –it does not matter how much you have of a specific compound or where it comes from the mass ratios
are always the same. If you have a 1.0 grams of NaCl or 100 grams of NaCl their mass ratios will always be 39.3 % by mass Na
combining with 60.7% by mass Cl.
(% mass of NaCl 1 atom of Na = 23.0amu 1 atom of Cl = 35.5 amu so NaCl would have a total mass of 58.5 amu
% mass of Na 23.0/58.5 = 39.3% % mass of Cl 35.5/58.5 = 60.7%)
Law of Multiple Proportions- Two elements can combine in different ratios (multiple) to form different compounds, NO, NO2, N2O3
Daltons Atomic Theory (1800’s)
1.
2.
3.
4.
5.
Matter is composed of extremely small particles called atoms. (Still true)
Atoms of a given element are identical in size, mass and other properties (Not true today, since Dalton we have discovered isotopes.
Isotopes are atoms of the same element that differ in number of neutrons and atomic mass KNOW-(Hydrogen has 3 isotopes,
protium 11H (1 proton and 0 neutrons), deuterium 21H (1 proton and 1 neutron), tritium 31H (1 proton and 2 neutrons)
Atoms cannot be subdivided, created, or destroyed (Not true today, since Dalton we now have nuclear reactions where we are able
to split the nucleus of the atom and create new atoms)
Atoms of different elements combine in simple whole number ratios to form compounds (Still true)
In chemical reactions, atoms are combined, separated, or rearranged. (Still true)
Structure of the Atom
Concept that atoms existed occurred around 400 BC by Aristotle and Democritus.
Atom- the smallest part of an element that retains the chemical properties of that element
Cathode Ray Tube Experiment-(Thomson-1897) led to the discovery and properties of electrons (cathode rays were stream of electrons that
traveled from the cathode (-) to the anode (+).
Proton discovered (Thomson- 1907)
Neutron discovered (Chadwick-1932)
Thomson’s Plum Pudding Model of the Atom compared to the modern model above. (1907)
Rutherford’s Gold Foil Experiment (1911)
Shot alpha (positive particles) through gold foil with most of the particles going straight through (proving the atom is mostly empty space) but
occasionally one of the alpha particles were deflected or bounced back (hitting a massive positive core, which he called the nucleus). Thus
discovering the positively charged nucleus.
We know that the nucleus of an atom is extremely massive and extremely small in size when compared to the overall size of the atom and has a
positive charge.
Nuclear Force: One would think that since the nucleus is made up of positive protons and neutral neutrons crammed into an extremely small
space, that the positive protons would repel each other being right next to each other, so what holds and prevents the nucleus from breaking
apart. Nuclear force is an extremely strong force which hold it together, much stronger than the repulsion force.
Size of atom: Imagine an atom magnified to the size of a football stadium. The nucleus of the atom would be the size of a pea in the center of
the stadium, and the electrons would be whizzing around the outer stands. Everything in between would be empty space.
Particle
Proton
Found
nucleus
Neutron
Nucleus
Electrons
Electron cloud outside nucleus
Mass number
1
(1.007 amu)
1
(1.009 amu)
0
(1/1836 that of a proton)
Charge
+
0
-
Atomic Number (Z) represents the number of protons in the nucleus and gives the atom its identity (no two different atoms have the same
number of protons) atomic # 3050X atomic number is the smaller number of the two numbers given in a nuclear symbol. The periodic table is
arranged based on atomic number.
Mass Number represents the number of protons and neutrons within the nucleus. Protons are given a mass of 1 amu, neutrons are given a
Mass number 50 X mass number is the larger number of the two numbers given in
mass of 1 amu, and electrons are assigned a mass of 0 amu.
30
a nuclear symbol
Isotopes are atoms of the same element that differ in the number of neutrons and thus differ in their mass numbers. Their chemical properties
do NOT differ. KNOW-(Hydrogen has 3 isotopes, protium 11H (1 proton and 0 neutrons), deuterium 21H (1 proton and 1 neutron), tritium 31H
(1 proton and 2 neutrons)
Calculating the number of protons-neutron and electrons
Atomic # = protons Mass # = Protons + Neutrons Neutral Atom (+ protons = - electrons)
Ions (charged atoms) Ca+2 cations P-3 anions (For an atom to become charged it must gain or lose electrons, NOT PROTONS) so Ca+2 has
LOST 2 electrons P-3 has GAINED 3 electrons
Nuclear symbol
80 Br
35
31 P-3
15
56
+3
26Fe
Atomic #
35
15
26
Mass #
80
31
56
Protons
35
15
26
Neutrons
45
16
30
Electrons
35
18
23
Average Atomic Mass (found on periodic table 56137.327Ba) 137.327 amu (atomic mass units, the units of mass of an atom) Average Atomic Mass
is the average mass of all the atoms isotopes and their relative abundance in nature (relative abundance is the % of how often that particular
isotope is found in nature)
Calculating A.A.M.
AAM = Mass Isotope (Relative Abundance) + Mass Isotope (Relative Abundance) +………
30
15X
56.17%
31 X
15
34.22%
31(0.3422) +
32 X
15
9.61%
32(0.0961) =
30(0.5617) +
30.5344 amu
100% (relative abundance must equal 100%)
Calculate the mass of the second isotope and its relative abundance given the average atomic mass to be 138.48 amu and the mass of one of
the isotopes to be 137.48 amu with its relative abundance 58.72%. AAM = Mass Isotope(Relative Abundance) + MI(RA)
137.48= 137.48(0.5872) + X (0.4128)100-58.72 (percent’s have to equal 100)
X = 137.48 amu
Calculate the relative abundance of each isotope given the average mass is 158.15 amu and the mass of the most abundant is 157.20 amu and
the second is 159.48 amu
AAM = Mass Isotope(Relative Abundance) + MI(RA)
158.15=157.20(X) + 159.48(1-X)since expressed as decimals instead of 100 use 1
158.15=157.20X + 159.48 – 159.48X
-1.33 = -2.28X
X = 58.33% 41.67%