Chemistry is scientific discipline:

1
Chemistry is scientific discipline a)
Experimental b) Empirical c) Exact
(quantitative) a) New achievements are derived
from results of experiments (analysis and
synthesis) b) New chemical results are compared
to experience of other scientific disciplines
(physics, mathematics, biology, philosophy,) c)
Results of chemical experiments are expressed in
quantitative systems of units and converted into
mathematical abstractions (laws, equations,
formulae, numbers) and then treated in this
representation by the rules valid for these
mathematical objects to gain new insight
theoretical chemistry.
2
What are the objects of interest for chemical
studies?
Matter
Constituents of the material sample
Multiple entities MIXTURE
Number of phases
1 Homogeneous mixtures
gt1 Heterogeneous mixtures
Separation of mixture components
Single chemical entity SUBSTANCE
Molecules COMPOUND
Synthesis
Atoms ELEMENT
Analysis
Elementary particles
Protons, neutrons, electrons (nucleus and
electron configuration)
ENERGY
3
ATOM
Nucleus
Electron shell
Most of the mass of the atom
Most of the atom chemical properties
Atom quality element name is determined by
the number of protons () in the nucleus.
Electrons organized in discrete orbitals
differing in energy that is required to place an
electron in the orbital.
Neutrons
Isotopes (mass)
Nucleus stability (radioactivity)
Energy to reorganize nucleons gtgtgtgt Energy to
reorganize electrons
Nuclear reactions (explosions)
Chemical reactions
4
Atomic composition of substances molecules
(that forms the matter anyway) explains the
empirically derived laws of definite proportions
and multiple proportions. Proportions of atoms
(integer numbers!) in any molecule define the
stoichiometry - first term used in chemistry to
describe molecular structure
Sulfurous acid H2SO3
5
How to go from a single atom/molecule to
macroscopic quantities of compounds ? Mass of
atom Mass(protons) Mass(neutrons)
Mass(neutrons) These masses can be experimentally
determined (physics, mass spectroscopy)
Mass(p) Mass(no) 1.674 x 10-24
g Mass(e-) 9.1094 x 10-31 g Largest
atom n(p) n(no) n(e-) 100 2 x 1.674 x
10-24 x 102 9.1094 x 10-31 x 102 3.35 x
10-22 Typical atom n(p) n(no) n(e-) 10 2
x 1.674 x 10-24 x 10 9.1094 x 10-31 x 10 3.35
x 10-23 If we have 1022 - 1023 atoms, the mass
of the sample will be in the order of grams
6
Quantitative approach Needed convenient but
exact unit to determine mass of atoms and
molecules (scale)
Invariant mass particular isotope of an
atom Why? See fractional abundance of isotopes
6 protons carbon 6 neutrons 12C isotope
Atomic mass unit mass of one nucleon 1/12 of
the mass of 12C atom
Mass of 12C atom 1.992648 x 10-23 g
To get the equivalent of mass of 1 nucleon in
grams we need NA 12C atoms so the mass of these
NA 12C atoms will be 12.0 grams.
Mathematically 1.992648 x 10-23 x NA 12.0 g
gt NA 12.0/ 1.992648 x 10-23 6.022 x 1023
Avogadros number
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In the same way as we call 12 eggs one dozen of
eggs, we call NA6.022 x 1023 eggs one MOLE of
eggs. Analogously, NA6.022 x 1023 students is
one MOLE of students, NA6.022 x 1023 bricks
is one MOLE of bricks and NA6.022 x 1023
molecules or atoms is one MOLE of
molecules/atoms. NO MYSTERY HERE!
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Stoichiometry of molecules counted in moles has
one important consequence from known number of
molecules and from their molecular formula we can
exactly calculate the number of individual atoms
that constitute the molecule
12x336 oxygen atoms 12x112 sulfur atoms 12x224
hydrogen atoms 12x672 atoms altogether
Dozen of sulfurous acid molecules 12 x H2SO3
NAx33 moles of oxygen atoms NAx11 mole of
sulfur atoms NAx22 moles of hydrogen
atoms NAx67 moles of atoms altogether
Mole of sulfurous acid molecules NA x H2SO3