INTRODUCTIONBasic Chemistry I

Gasal 2011/2012

Chemistry 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 whenyou 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 composi-

tion)

Mixture of two or more substances

Elements Compounds

Solutions(homogenous

composition-onephase)

HeterogenousMixture (two orMore 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 TheoryAnd 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) & othersno 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 RutherfordNuclear 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

Electron

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 atom of an element

mass

number

atomic number

XA

Z

• 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

Mass of substance moles

Number ofatomsMolar mass

Avogadro’s

number

x x

: :

• 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