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 + O2  2 H2O
- Hydrogen & Oxygen as the reactants or starting
materials
- Water is the reaction product
- Balanced chemical equation
(g)

(g)

(l)

• 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