Download INTRODUCTION Basic Chemistry I

INTRODUCTION
Basic Chemistry I
Gasal 2011/2012
Chemistry
?
• The science of composition, structure,
properties, and reaction of matter.
• The science that deals with the materials of the
universe and the changes that these materials
undergo.
• Not only concern with the composition and
changes in composition of matter, but also with
the energy & energy changes associated with
matter.
• Why do we have to study chemistry?
• What’s the relevance with food science?
The branches of chemistry
1.
2.
Inorganic chemistry
It deals with all elements but carbon, as well as
with some carbon compounds  derived mainly
from mineral sources.
Organic chemistry
Concern with compounds containing the element
carbon  derived from living organisms.
Why does soda fizz when
you open the bottle?
How to make candy?
How pop corn pops?
• Popcorn kernels contain oil and water with starch, surrounded
by a hard and strong outer coating.
• When popcorn is heated, the water inside the kernel tries to
expand into steam, but it cannot escape through the seed
coat (the popcorn hull).
• The hot oil and steam gelatinizes the starch inside the
popcorn kernel, making it softer and more pliable.
• When the popcorn reaches a temperature of 180 °C (356 °F)
the pressure inside the kernel is around 135 psi (930 kPa),
which is sufficient pressure to rupture the popcorn hull,
essentially turning the kernel inside-out. The pressure inside
the kernel is released very quickly, expanding the proteins
and starch inside the popcorn kernel into a foam, which cools
and sets into the familiar popcorn puff.
Liquid Nitrogen Ice Cream
• When we make liquid
nitrogen ice cream the
nitrogen boils off
harmlessly into the air
rather than becoming an
ingredient in the recipe.
• Nitrogen is used to cool
ice cream so that you
don't have to wait around
for a freezer or ice cream
maker.
Classification and
Properties of Matter
Matter:
- anything that has mass & occupies space.
- It exists in 3 physical states: solid, liquid & gas.
Substance:
A particular kind of matter
with a definite, fixed
composition.
Element:
• A substance that cannot be broken down into other
substances by chemical methods.
• Examples of elements are iron, aluminum, oxygen, and
hydrogen.
• Elements are defined by the number of protons they
possess.
Compound:
• A substance compose of a given combination of
elements that can be broken down into those elements
by chemical methods. Ex: water
Mixture:
• Something that has variable composition.
• Mixtures can be separated into pure substances:
elements and/or compounds.
• Mixtures can be classified as either homogeneous (ex:
salt solution) or heterogeneous.
Matter
Pure substances
(homogenous composition)
Elements
Compounds
Mixture of two or
more substances
Solutions
(homogenous
composition-one
phase)
Heterogenous
Mixture (two or
More phases)
Atom
 the fundamental unit of a chemical substance
(Greek, atomos: uncut-able)
 An atom is the smallest possible particle of an
element; extremely small
Molecule
 A combination of two or more atoms held
together in a specific shape by attractive forces
 Most chemistry deals with the behavior of
molecules
Atomic Theory
And Structure
The development of atomic theory
• Democritus (470-380 BC)
atomos: indivisible; the smallest bit of matter that cannot be
divided further
• Aristotle (384-322 BC) & others
no matter how small the portion of matter, it remains uniform
in composition.
• John Dalton (1766-1844)
• J. Jakob Berzelius (1779-1848)
Substances always combine in fixed proportions
• J.J. Thomson (1890s)
The atoms of any element can be made to emit
tiny negative particles, called electrons.
• Ernest Rutherford
Nuclear atom—an atom with a dense center of
positive charge (the nucleus) around which tiny
electrons moved in a space that was otherwise
empty.
Atomic theory
• The essential features of atoms:
- all matter is composed of tiny particles called atoms
- all atoms of a given element have identical chemical
properties
- atoms of different elements have distinct properties
- atoms form chemical compounds by combining in
whole-number ratios. All samples of a pure compound
have the same combination of atoms
- in chemical reactions, atoms change the ways they
are combined, but they are neither created or
destroyed
- Water always contains 1.0 g of hydrogen for every
8.0 g of oxygen  the composition doesn’t
change although the amount does.
2 H2(g) + O2(g)  2 H2O(l)
- Hydrogen & Oxygen as the reactants or starting
materials
- Water is the reaction product
- Balanced chemical equation
• Atoms combine (in whole-number ratios) to make
compounds
• Atoms are constantly in motion
- Brownian motion (1828, Robert Brown)
- Diffusion of one liquid into another
• Dynamic equilibrium
- A system at equilibrium shows no change in its
observable properties
A dynamic system contains objects
that move continuously
Atomic architecture
- Are atoms made of other, still smaller particles, and
if they are, what are these particles?
- How are atoms bound together in chemical
compounds?
• Gravitational force
- Every mass exerts a gravitational attraction on all
other masses
• Electrical force
- For tiny objects electrical for is the most important
Coulomb’s law
• Magnetism
- A charged object in motion is also subject to
magnetism
• Electrons
- Experiments that used electrical force 
electrodes  atoms are made up of smaller
fragments that possess + & - charges
- J.J.Thomson  a cathode ray tube  able
to calculate
- Robert A. Millikan  mass of single electron
• The nucleus
- 1909, Ernest Rutherford: every atom contains a
tiny central core where all the positive charge &
most of the mass is concentrated
- Nucleus is surrounded by the electrons
- Nucleus contains 2 types of subatomic fragments:
protons & neutrons
- Protons  positive charges of nuclei
- Neutrons  contribute mass but are electrically
neutral
- A proton’s positive charge is equal in magnitude to
the negative charge of an electron
- The mass of a proton is almost 2000 times greater
than the mass of electron
Atomic building blocks
Name
Symbol
Charge
Mass
Electro
n
Proton
e
-1.6022 x 10-19 C
p
Neutron
n
+1.6022 x 10-19
C
0
9.1094 x 10-31
kg
1.6726 x 10-27
kg
1.6749 x 10-27
kg
Atomic diversity
• An element is identified by the charge of its nucleus
- every elements has specific & unchanging number of
protons ( atomic number - Z).
- ex.: Hydrogen (Z=1), Helium (Z=2), etc  see
- Mass number (A  g/mol) is the total number of
neutrons and protons presents in the nucleus of an
atom of an element
mass
number
A
Z
X
atomic number
• Isotopes
- Two atoms with the same number of protons but
different numbers of neutrons
- Usually specified by giving its mass number (A)
- E.g.: hydrogen, uranium
• Atomic masses
• The mass of an atom is related to the number of
electrons, protons and neutrons in the atom 
atomic mass unit (amu).
• We usually use the average atomic mass.
• Molar mass of an element & Avogadro’s number
• One mole is the number of atoms in exactly 12g
of the pure isotope carbon-12
• Using mass spectrometers, the mass of a 12C
atom is m = 1.992648 x 10-23 g/atom. Combining
this experimental mass with the definition of the
mole gives the number of atoms in one mole.
• (12g 12C/mol) / (1.992648 x 10-23g 12C/atom) =
6.022137 x 1023 atoms/mol
 Avogadro’s number (N, No, or NA)
• Mass-Mole-Atom Conversions
x
Mass of
substance
Molar mass
x
moles
Avogadro’s
number
:
:
Number of
atoms
• Empirical formula
Indicates which elements are present and the
simplest whole-number ratio of their atoms.
Ex:
Hydrogen peroxide (H2O2)  2 atoms H & 2
atoms O  ratio H:O = 2:2 or 1:1  the
empirical formula is HO.
Hydrazine (N2H4 )  NH2
• Molecular mass
The sum of the atomic masses in the molecule.
Charged atoms : Ions
• When is an atom called neutral?
• Ion? Atomic or molecular particles with
electrical charge
• Ionic compounds
- The simplest collection of oppositely charged
ions is a solid in which the cations & anions
alternate in a regular pattern
- Ionic compound contains cations & anions in
fixed whole-number ratios
- Example: Sodium chloride (NaCl)
Conservation laws
• Conservation of atoms
- Atoms are neither created nor destroyed
- Atoms are conserved in chemical & physical
processes
• Conservation of electrons
• Conservation of mass
- Mass is neither created nor destroyed during
physical & chemical transformations
 The conservation of atoms, electrons, & mass is
the fundamental principle of stochiometry
 Conservation of energy:
“Energy is neither created nor destroyed in any
process, although it may be transferred from
one body to another or converted from one
form into another”.
 Forms of energy:
- Kinetic energy
- Potential energy
- Chemical energy
- Thermal energy
- Radiant energy