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