the great variety of colors in a garden scene the texture of the fabric in your clothes
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Look Around You. The great variety of colors in a garden scene The texture of the fabric in your clothes The solubility of sugar in a cup of coffee The transparency of a window. How Do We Explain?. - PowerPoint PPT PresentationTRANSCRIPT
The great variety of colors in a garden scene
The texture of the fabric in your clothes
The solubility of sugar in a cup of coffee
The transparency of a window
LOOK AROUND YOU
What makes diamonds transparent and hard,
while table salt is brittle and dissolves in water?
Why does paper burn, and why does water
quench fires?
Where does the beautiful colors of flowers come
from?
The structure and behavior of atoms are key to
understanding the properties of matter.
HOW DO WE EXPLAIN?
The diverse properties results from only about 100 different elements
How do atoms combine with one another? What rules govern the ways in which atoms can
combine? How do the properties of a substance relate to
the kinds of atoms it contains? What is an atom like, and what make their
difference?
VARIETY OF ELEMENTS
2.1 THE ATOMIC THEORY OF MATTER
Democritus and Greek philosophers (BC 400)•The material world must be made up of tiny indivisible
particles•atomos: indivisible or uncuttable
Plato and Aristotle• There can be no ultimately indivisible particles• The “atomic” view of matter faded for many centuries
Newton (1642-1727)• Air is composed of something invisible and in constant
motion• Still very different from thinking of atoms as the
fundamental building blocks
HISTORY
Chemists learned to measure the amounts of elements
that reacts with one another to form new substances
Dalton’s atomic theory
•Introduced during the period from 1803 to 1807
•The theory was based on the four postulates given in
the figure in the next page
2.1 THE ATOMIC THEORY OF MATTER
DALTON’S ATOMIC THEORY
Dalton’s theory explains several simple laws of chemical combination.
The law of constant composition• In a given compound, the relative numbers and kinds of
atoms are constant The law of conservation of mass (matter)
• The total mass of materials present after a chemical reaction is the same as the total mass present before the reaction
The law of multiple proportions• If two elements A and B combine to form more than one
compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers (H2O and H2O2)
2.1 THE ATOMIC THEORY OF MATTERDALTON’S
POSTULATES
2.2 THE DISCOVERY OF ATOMIC STRUCTURE
Dalton had no direct evidence for the existence of atoms Scientists have developed methods for more detailed
probing of the nature of matter Today, we can measure the properties of individual
atoms and even provide images of them
FIGURE 2.2 An image of the surface of silicon obtained by scanning tunneling microscopy (STM)
ATOMIC IMAGES
CATHODE RAYS AND ELECTRONS Thomson found that cathode rays are streams of
negatively charged particles
2.2 THE DISCOVERY OF ATOMIC STRUCTURE
CATHODE RAYS AND ELECTRONS
The charge/mass ratio: 1.76 X 108 C/g
2.2 THE DISCOVERY OF ATOMIC STRUCTURE
MILLIKAN’S OIL DROP EXPERIMENT Robert Millikan (University of Chicago) determined the
charge on the electron in 1909.
2.2 THE DISCOVERY OF ATOMIC STRUCTURE
Radioactivity is the spontaneous emission of radiation by an atom.
It was first observed by Henri Becquerel. Marie and Pierre Curie also studied it. Three types of radiation were discovered by Ernest Rutherford:
• a particles• b particles• g rays
RADIOACTIVITY 2.2 THE DISCOVERY OF ATOMIC STRUCTURE
The prevailing theory was that of the “plum pudding” model, put forward by Thomson.
It featured a positive sphere of matter with negative electrons imbedded in it.
THE NUCLEAR MODEL2.2 THE DISCOVERY OF ATOMIC STRUCTURE
Ernest Rutherford shot a particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.
THE NUCLEAR MODEL2.2 THE DISCOVERY OF ATOMIC STRUCTURE
THE NUCLEAR MODEL Since some particles were deflected
at large angles, Thompson’s model could not be correct.
Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom.
Most of the volume of the atom is empty space.
Protons were discovered by Rutherford in 1919.
Neutrons were discovered by James Chadwick in 1932.
2.2 THE DISCOVERY OF ATOMIC STRUCTURE
2.3 THE MODERN VIEW OF ATOMIC STRUCTURE
SUBATOMIC PARTICLES Protons and electrons are the only particles that have a
charge. Protons and neutrons have the same mass. The mass of an electron is so small we ignore it.
FIGURE 2.11 The structure of an atom.
SUBATOMIC PARTICLES Every atom has an equal number of electrons and
protons, so atoms have no net charge.
Atomic mass unit, 1 amu = 1.66054 X 10-24 g
Atom’s size: 1-5 Å
2.3 THE MODERN VIEW OF ATOMIC STRUCTURE
Sample Exercise 2.1 Atomic Size
The diameter of a US dime is 19 mm, and the diameter of a silver atom is 2.88 Å. How many silver atoms could be arranged side by side across the diameter of a dime?
The diameter of a carbon atom is 1.54 Å. (a) Express this diameter in picometers. (b) How many carbon atoms could be aligned side by side across the width of a pencil line that is 0.20 mm wide?
Practice Exercise
2.3 THE MODERN VIEW OF ATOMIC STRUCTURE
THE DIAMETERS OF ATOMIC NUCLEI About 10-4 Å
Density of nucleus: 1013 ~ 1014 g/cm3
A match box full of nuclei would weigh over 2.5 billion tons!
2.3 THE MODERN VIEW OF ATOMIC STRUCTURE
ATOMIC NUMBERS, MASS NUMBERS, & ISOTOPES What makes the difference between carbon and oxygen?
•The atoms of each element have a characteristic number of protons
Atomic number: the number of protons in the nucleus Isotopes: atoms with identical atomic numbers but different
mass numbers.
2.3 THE MODERN VIEW OF ATOMIC STRUCTURE
2.5 THE PERIODIC TABLE
The most significant tool that chemists use for organizing and remembering chemical facts
2.4 ATOMIC WEIGHTS
THE ATOMIC MASS SCALE The atomic mass unit (amu)
•Defined by assigning a mass of exactly 12 amu to an atom of 12C
1H: 1.0078 amu, 16O: 15.9949 amu
AVERAGE ATOMIC MASSES Most elements occur in nature as mixtures of isotopes. 12C: 98.93%, 13C : 1.07%
(0.9893)(12 amu) + (0.0107)(13.00335 amu) = 12.01 amuatomic weight
▲FIGURE 2.12 A mass spectrometer. ▲FIGURE 2.12 Mass spectrum of atomic chlorine.
2.5 THE PERIODIC TABLE
Many elements show very strong similarities to one another When one looks at the chemical properties of elements,
one notices a repeating pattern of reactivities.
PERIODICITY
2.5 THE PERIODIC TABLE
The most significant tool that chemists use for organizing and remembering chemical facts
It is a systematic catalog of the elements. Elements are arranged in order of atomic number.
2.5 THE PERIODIC TABLE
The rows on the periodic chart are periods.
Columns are groups.
Elements in the same group have similar chemical properties.
2.5 THE PERIODIC TABLE
Many groups are known by their names. “Coinage metals”: Group 11
2.5 THE PERIODIC TABLEGROUPS
2.5 THE PERIODIC TABLEMETALS, NONMETALS, AND METALLOIDS
Nonmetals generally differ from the metals in appearance and in other physical properties.
A metalloid is a chemical element with properties that are in-between or a mixture of those of metals and nonmetals
2.5 THE PERIODIC TABLE
◄ FIGURE 2.17
Isolated Pu Identified the elements having
atomic numbers 95 through 102 Identified element
number 106 ACS proposed
that element number 106 be named seaborgium
2.6 MOLECULES AND MOLECULAR COMPOUNDSMOLECULES
Only the noble-gas elements are normally found in nature as isolated atoms.
A molecule is an assembly of two or more atoms tightly bound together.
Molecules behave in many ways as a single, distinct object
atoms
a molecule
2.6 MOLECULES AND MOLECULAR COMPOUNDSMOLECULES AND CHEMICAL FORMULAS
Many elements are found in nature in molecular form
Two different molecular forms of oxygen•O2: a diatomic molecule, essential for life, odorless•O3: a triatomic molecule, toxic, pungent smell
Diatomic molecules
2.6 MOLECULES AND MOLECULAR COMPOUNDSMOLECULES AND CHEMICAL FORMULAS
Molecular compounds are composed of two or more different atoms
Molecules vs Compounds Most molecular substances that we will
encounter contain only nonmetals.
2.6 MOLECULES AND MOLECULAR COMPOUNDS
MOLECULAR AND EMPIRICAL FORMULAS Molecular formulas
•H2O•H2O2
•C2H4
•C6H12O6
Empirical formulas•H2O•HO•CH2
•CH2O
Why do we need empirical formulas?•Certain common methods of analyzing
substances lead to the empirical formula only
2.6 MOLECULES AND MOLECULAR COMPOUNDS
PICTURING MOLECULES A structural formula shows which
atoms are attached to which within the molecule.
A perspective drawing gives some sense of three dimensional shape
Ball-and-stick models show the accurate angles between bonds
A space-filling model shows the relative sizes of the atoms.
When atoms lose or gain electrons, they become ions.• Cations are positive and are formed by elements on the
left side of the periodic chart (metal atoms).• Anions are negative and are formed by elements on the
right side of the periodic chart (nonmetal atoms).
2.7 IONS AND IONIC COMPOUNDS
CATIONS AND ANIONS
Many atoms gain or lose e- to make the same number of e- as the noble gas.
PREDICTING IONIC CHARGES
2.7 IONS AND IONIC COMPOUNDS
Figure 2.20. Predictable charges of some common ions
A compound that contains both positively and negatively charged ions.
Generally combinations of metals and nonmetals
IONIC COMPOUNDS
2.7 IONS AND IONIC COMPOUNDS
WRITING EMPIRICAL FORMULAS FOR IONIC COMPOUNDS
2.7 IONS AND IONIC COMPOUNDS
The ionic compound formed from Mg2+ and N3-
97% of the mass of most organisms: O, C, H, N, P, and S 70% of the mass of most cells: H2O C is the most prevalent element in the solid components of
cells
NAMES AND FORMULAS OF IONIC COMPOUNDS
2.8 NAMING INORGANIC COMPOUNDS
Positive ions (Cations)•Cations formed from metal atoms
•Ions of the same element that have different charges exhibit different properties
•Metals that form only one cation - group 1A/2A, Al3+, Ag+, Zn2+ • Cations from nonmetals
2.8 NAMING INORGANIC COMPOUNDS
Fe(II)
Fe(III)
NAMES AND FORMULAS OF IONIC COMPOUNDS
2.8 NAMING INORGANIC COMPOUNDS
Negative ions (Anions)•Monatomic and simple polyatomic anions
•Oxyanions
NAMES AND FORMULAS OF IONIC COMPOUNDS
2.8 NAMING INORGANIC COMPOUNDS
Negative ions (Anions)•Anions containing H+
•Older method: HCO3
- bicarbonate ion; HSO4- bisulfate ion
(a) SeO42- (b) SeO3
2-
2.8 NAMING INORGANIC COMPOUNDS
NAMES AND FORMULAS OF IONIC COMPOUNDS
2.8 NAMING INORGANIC COMPOUNDS
Ionic compounds•Cation name followed by anion name
NAMES AND FORMULAS OF ACIDS2.8 NAMING INORGANIC COMPOUNDS
NAMES AND FORMULAS OF ACIDS2.8 NAMING INORGANIC COMPOUNDS
(a) Hydrocyanic acid or hydrogen cyanide.(b) Nitric acid(c) Sulfuric acid.(d) Sulfurous acid
(a) HBr, (b) H2CO3
NAMES AND FORMULAS OF BINARY MOLECULAR
COMPOUNDS
2.8 NAMING INORGANIC COMPOUNDS
(a) sulfur dioxide, (b) phosphorus pentachloride, and (c) dichlorine trioxide.
(a) SiBr4, (b) S2Cl2
ALKANES2.9 SOME SIMPLE ORGANIC COMPOUNDS
Organic compounds•Compounds that contain carbon
Alkanes•Compounds that contain only carbon and hydrogen
SOME DERIVATIVES OF ALKANES2.9 SOME SIMPLE ORGANIC COMPOUNDS
An alcohol is obtained by replacing an H atom with a –OH group