Chapter 4 Atoms, Ions, and Compounds. The Composition of Compounds The law of multiple proportions...

transcript

Chapter 4Atoms, Ions, and Compounds

The Composition of Compounds• The law of multiple proportions states

that the masses of element Y that combine with a fixed mass of elements X to form two or more different compounds are in the ratios of small whole numbers.

• Examples: NO, NO2, N2O, N2O5, etc.

Atomic Structure• J. J. Thomson discovered the subatomic

particle know as the electron.• Thomson used cathode ray tube.

Mass of An Electron• Robert Millikan

determined the mass of an electron with his oil-droplet experiment.

Thomson Model of the Atom• J. J. Thomson’s Plum-pudding model of the atom.

Radioactivity and the Nuclear Atom• Henri Becquerel discovered that some

samples produced invisible radiation.• One type is a steam of beta () particles

(high energy electrons).• A second type consists of alpha ()

particles, which have a +2 charge and a mass equivalent to that of a helium nucleus.

Rutherford’s Experiment• Rutherford and two of his students

bombarded a thin foil of gold with particles to test Thomson’s model of the atom.

• Theory would predict that the particles would travel through the foil without deflection, but the results didn’t confirm the model.

Rutherford’s Experiment

The Nuclear Atom• The nucleus of an atom contains all the

positive charge and nearly all the mass in an atom.

• The nucleus is about 1/10,000 the size of the atom.

• A proton is a positively charged subatomic particle present in the nucleus of an atom.

The Third Subatomic Particle• A neutron is an electrically neutral or

uncharged subatomic particle found in the nucleus of an atom.

• Atomic Mass Units (amu) comprise a relative scale used to express the masses of atoms and subatomic particles.

• The scale is based on the definition that the mass of 1 atom of carbon with 6 protons and 6 neutrons in its nucleus is exactly 12 amu.

Aston’s Experiment• Francis W. Aston built a postive-ray analyzer.

• Data from neon gas samples demonstrated that two different kinds of atoms or isotopes existed.

• Isotopes are atoms of an element whose nuclei have the same number of protons but different numbers of neutrons.

Aston’s Positive-ray Analyzer

• Elements are pure substances made up of identical atoms.

• There are 115 known kinds of atoms. Each has its own symbol.

• The first character in an atoms symbol is an uppercase letter that corresponds the first letter of the elements name.

• Most elements have a second character in their symbol which is is a lowercase letter usually the second letter of the elements name.

Elements

Symbol and names for the known atoms are given in Table 2.1.

Elements discovered long ago have names and symbols with Latin or other origins, such as Au for gold (from aurum, meaning “bright dawn”), or Pb for lead (plumbum). Tungsten has a symbol of W, which is the first letter of its German name, wolfram.

Element Names

The symbol and names for

the known atoms are given

in Table 2.1.

Symbols of Isotopes• Each element consists of atoms with the

same number of protons in the nucleus. This number is called atomic number (Z).

• Protons and neutrons in atomic nuclei are called nucleons.

• The mass number (A) is the total number nucleons in one atom of an element.

Writing the Symbol of an Isotope

• A is the mass number

• Z is the atomic number

• X is the atomic symbol

Average Atomic Masses

• A mass spectrometer is an instrument that measures precise masses and relative amounts of ions of atoms and molecule.

• The natural abundance of an isotope is its relative proportion among all the isotopes found a natural sample.

• The average atomic mass of an element is calculated by multiplying the natural abundance of each isotope by its exact mass in atomic mass units and then summing these products.

ExampleIsotope Mass (amu) Natural abundance (%)

Neon-20 19.9924 90.4838Neon-21 20.99395 0.2696Neon-22 21.9914 9.2465

Neon is found in three isotopes in nature.

19.9924 x 0.904838 = 20.99395 x 0.002696 =21.9914 x 0.092465 =

18.0898323 amu0.056599689 amu2.033434801 amu

20.1797 amu

Mendeleev’s Periodic Table• Dmitrii I. Mendeleev

arranged elements in the periodic table by their chemical and physical properties.

• He left open spaces in his periodic table to account for elements not yet discovered.

The Modern Periodic Table• The modern periodic table is also based on a

classification of elements in terms of their physical and chemical properties.

• The horizontal rows are called periods.• Columns contain elements of the same family

or group.• Transition metals are the elements in group 3

through 12 in the periodic table.

Groups of Elements• Group 1 contains the alkali metals.

• Group 2 contains the alkaline earth metals.

• Group 17 contains the halogens.

Broad Categories of Elements• Metals are elements on the left-hand side of

the table. Metals are shiny solids that conduct heat and

electricity well and are malleable and ductile.

• Nonmetals have properties opposite to those of the metals and are on the right side of table

• Metalloids are the elements between the metals and nonmetals.

Continued

• Main group elements or representative elements are the elements in groups 1,2 and 13 through 18.

• The noble gases are the elements in Group 18.

Kinds of Compounds• Molecular Compounds are composed of

atoms held together by covalent bonds.• Covalent bonds are shared pairs of electrons

that chemically bond atoms together.• Ionic Compounds are composed of positively

and negatively charged ions that are held together by electrostatic attraction.

• Ions with negative charge are called anions.• Ions with positive charge are called cations.

Continued• Molecular compounds are made of

nonmetals

• Ionic compounds are made of a metal and a nonmetal.

• Metal form cations and nonmetals form anions.

Terms• Molecular formulas describe the exact

number and type of atoms present in one molecule of a compound.

• An empirical formula gives the simplest whole-number ratio of elements in a compound.

• The formula unit of an ionic compound is the smallest electrically neutral unit within the crystal of the compound.

Binary means two different elements

Ionic means metal and nonmetal

Step 1First give the name of the metal, followed by thenonmetal name using the “ide” suffix.

Step 2 If the metal is to the right of group IIA, then aRoman numeral is used after the metal to todescribe the charge of the metal. Except Ag,Zn,and Al

ExamplesNaCl Al2O3

FeCl2 FeCl3

NOMENCLATUREI. Binary Ionic compounds

ExamplesNaCl Sodium chloride Al2O3

FeCl2 FeCl3

ExamplesNaCl Sodium chloride Al2O3 Aluminum oxide

FeCl2 FeCl3

FeCl2 Iron(II) chloride FeCl3

FeCl2 Iron(II) chloride FeCl3 iron(III) chloride

II. Nonbinary Ionic compoundsNonbinary means more than two different elements

Step 1First give the name of the metal, followed by the memorized polyatomic ion name.

Step 2

If the metal is to the right of group IIA, then aRoman numeral is used after the metal to describe the charge of the metal. Except Ag, Zn, and Al.

ExamplesNaOH Fe(NO3)3

Fe(SO4)2Zn(C2H3O2)2

Formula Name Formula NameNH4

+ Ammonium O22- Peroxide

C2H3O2- Acetate NO3

- NitrateCO3

2- Carbonate NO2- Nitrite

HCO31- Hydorgen

carbonateSO4

2- Sulfate

ClO4- Perchlorate SO3

2- SulfiteClO3

- Chlorate PO43- Phosphate

ClO2- Chlorite PO3

3- PhosphiteClO- Hypochlorite CrO4

2- ChromateCN- Cyanide Cr2O7

2- DichromateOH- Hydroxide

Memorized Polyatomic Ion List

Step 2

Fe(SO4)2Zn(C2H3O2)2

Sodium hydroxide

Step 2

Fe(SO4)2Zn(C2H3O2)2

Sodium hydroxide

Iron(III) nitrate

Step 2

Fe(SO4)2Zn(C2H3O2)2

Sodium hydroxide

Iron(III) nitrate

Iron(II) sulfate

Step 2

Fe(SO4)2Zn(C2H3O2)2

Sodium hydroxide

Iron(III) nitrate

Iron(II) sulfate Iron(II) sulfate

III. Binary molecular Compounds

Step 1First give the name of the first nonmetal,followed by the nonmetal name using the “ide”

suffix.Step 2

Give each nonmetal a Latin prefix describing the number of atoms present in the compound.

ExamplesCO CO2

P2O5 CCl4

Molecular means nonmetals

You will need to learn the Greek numerical prefixes (Table 4.6):

Number Prefix1 Mono-*2 Di-3 Tri-4 Tetra-5 Penta-6 Hexa-7 Hepta-8 Octa-9 Nona-

10 Deca-

*Note 1 Compound names never start with mono

Note 2 When adding a prefix two vowls cannot next to each other

III. Binary Molecular Compounds

suffix.Step 2

ExamplesCO Carbon monoxide CO2

P2O5 CCl4

suffix.Step 2

ExamplesCO Carbon monoxide CO2 Carbon dioxide

P2O5 CCl4

suffix.Step 2

P2O5 CCl4

II. Binary Ionic molecular

suffix.Step 2

P2O5 Diphosphorus Pentoxide

Molecular means combination of nonmetals

II. Binary Ionic molecular

suffix.Step 2

P2O5 Diphosphorus Pentoxide

CCl4 Carbon tetrachloride

Molecular means combination of nonmetals

III. Nonbinary Molecular Compounds

Step 1Write down the memorized polyatomic ions present in the compound.

Step 2

Look to see if any monatomic ions are present. If so, then cations use the normal name. If it is an anion, then its name comes last with the “ide” suffix.

Examples

Note: Do not use Latin prefixes

Step 2

Examples

Ammonium chloride

Step 2

Examples

Ammonium chloride

Ammonium hydroxide

Compounds that Start with HydrogenCase 1

Case 2

Case 3

Case 4

If the anion ends in “ide” and it is aqueous, then use the prefix hydro and suffix “ic acid”

If the anion ends in “ate” then drop it and add the suffix “ic acid”

If the anion ends in “ite” then drop it and add the suffix “ous acid”

If the anion ends in” ide” and is a gas, or liquid, then leave the name and do not use Latin prefiex

Compounds that Start with HydrogenExamples

HCl (aq)

H2O (l)

HCl (aq)

H2O (l)

HCl (aq)

chloride

HCl (aq)

H2O (l)

HCl (aq)

chloride chloric acid

HCl (aq)

H2O (l)

HCl (aq)

chloride chloric acid hydrochloric acid

HCl (aq)

H2O (l)

HCl (aq)

nitrate

HCl (aq)

H2O (l)

HCl (aq)

nitrate nitric acid

HCl (aq)

H2O (l)

HCl (aq)

nitrate nitric acid

nitrite

HCl (aq)

H2O (l)

HCl (aq)

nitrate nitric acid

nitrite nitrous acid

HCl (aq)

H2O (l)

HCl (aq)

nitrate nitric acid

HCl (aq)

H2O (l)

HCl (aq)

nitrate nitric acid

oxide hydrogen oxide

HCl (aq)

H2O (l)

HCl (aq)

nitrate nitric acid

chloride

HCl (aq)

H2O (l)

HCl (aq)

nitrate nitric acid

chloride hydrogenchloride

The End

Chapter 4 Atoms, Ions, and Compounds. The Composition of Compounds The law of multiple proportions...

Documents