INTRODUCTION basic chemistry i

 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 mor

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 Inorganic chemistry

It deals with all elements but carbon, as well as with some carbon compounds  derived mainly from mineral sources.

2 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

- 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.

• 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

• 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.

Elements Compounds

Solutions (homogenous composition-one

phase)

Heterogenous Mixture (two or More phases)

 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)

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

• 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

Atomic building blocks

Name Symbol Charge Mass

Electro

n e -1.6022 x 10

-19 C 9.1094 x 10 -31 kg Proton p +1.6022 x 10 -19 C 1.6726 x 10 -27 kg Neutron n 0 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

• 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

• Mass-Mole-Atom Conversions

Mass of

substance moles

Number of atoms Molar mass Avogadro’s

number

• 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”