INTRODUCTION basic chemistry i

39 4 0
  • Loading ...
1/39 trang

Thông tin tài liệu

Ngày đăng: 01/12/2016, 23:40

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 we have to study chemistry? • What’s the relevance with food science? The branches of chemistry 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 • 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 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 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 Mass 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)  atoms H & 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 [...]... 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...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... 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... 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) ... • 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... 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... 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... 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... 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... 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
- Xem thêm -

Xem thêm: INTRODUCTION basic chemistry i , INTRODUCTION basic chemistry i , INTRODUCTION basic chemistry i

Gợi ý tài liệu liên quan cho bạn

Nạp tiền Tải lên
Đăng ký
Đăng nhập