Chapter 2 Atoms, Molecules and Ions

Outline Atoms and Atomic Theory Atoms and Atomic Theory Components of the Atom Components of the Atom Quantitative Properties of the Atom Quantitative Properties of the Atom Introduction to the Periodic Table Introduction to the Periodic Table Molecules and Ions Molecules and Ions Formulas of Ionic Compounds Formulas of Ionic Compounds Names of Compounds Names of Compounds

The Structure of Matter Atoms Atoms Composed of electrons, protons and neutrons Composed of electrons, protons and neutrons Molecules Molecules Combinations of atoms Combinations of atoms Ions Ions Charged particles Charged particles

Atoms and Atomic Theory An element is composed of tiny particles called atoms An element is composed of tiny particles called atoms All atoms of the same element have the same chemical properties All atoms of the same element have the same chemical properties In an ordinary chemical reaction In an ordinary chemical reaction There is a change in the way atoms are combined with each other There is a change in the way atoms are combined with each other Atoms are not created or destroyed Atoms are not created or destroyed Compounds are formed when two or more atoms of different elements combine Compounds are formed when two or more atoms of different elements combine

Figure John Dalton and Atomic Theory

Fundamental Laws of Matter There are three fundamental laws of matter There are three fundamental laws of matter Law of conservation of mass Law of conservation of mass Matter is conserved in chemical reactions Matter is conserved in chemical reactions Law of constant composition Law of constant composition Pure water has the same composition everywhere Pure water has the same composition everywhere Law of multiple proportions Law of multiple proportions Compare Cr 2 O 3 to CrO 3 Compare Cr 2 O 3 to CrO 3 The ratio of Cr:O between the two compounds is a small whole number The ratio of Cr:O between the two compounds is a small whole number

Figure A – The Law of Multiple Proportions Two different oxides of chromium

Fundamental Experiments J.J. Thomson, Cavendish Laboratories, Cambridge, England J.J. Thomson, Cavendish Laboratories, Cambridge, England Ernest Rutherford Ernest Rutherford McGill University, Canada McGill University, Canada Manchester and Cambridge Universities, England Manchester and Cambridge Universities, England

Electrons First evidence for subatomic particles came from the study of the conduction of electricity by gases at low pressures First evidence for subatomic particles came from the study of the conduction of electricity by gases at low pressures J.J. Thomson, 1897 J.J. Thomson, 1897 Rays emitted were called cathode rays Rays emitted were called cathode rays Rays are composed of negatively charged particles called electrons Rays are composed of negatively charged particles called electrons Electrons carry unit negative charge (-1) and have a very small mass (1/2000 the lightest atomic mass) Electrons carry unit negative charge (-1) and have a very small mass (1/2000 the lightest atomic mass)

Figure 2.3 – Cathode Ray Apparatus

The Electron and the Atom Every atom has at least one electron Every atom has at least one electron Atoms are known that have one hundred or more electrons Atoms are known that have one hundred or more electrons There is one electron for each positive charge in an atom There is one electron for each positive charge in an atom Electrical neutrality is maintained Electrical neutrality is maintained

The Plum-Pudding Model J.J. Thomson proposed the atom as a positively charged sphere J.J. Thomson proposed the atom as a positively charged sphere Within the sphere are electrons Within the sphere are electrons Plum-pudding or raisin- bread model Plum-pudding or raisin- bread model

Protons and Neutrons – The Nucleus Ernest Rutherford, 1911 Ernest Rutherford, 1911 Bombardment of gold foil with α particles (helium atoms without electrons) Bombardment of gold foil with α particles (helium atoms without electrons) Expected to see the particles pass through the foil Expected to see the particles pass through the foil Found that some of the alpha particles were deflected by the foil Found that some of the alpha particles were deflected by the foil Led to the discovery of a region of heavy mass at the center of the atom Led to the discovery of a region of heavy mass at the center of the atom

Figure 2.5 – Rutherford Backscattering

Rutherford’s Model Rutherford’s experiment revealed a small, dense core with positive charge Rutherford’s experiment revealed a small, dense core with positive charge Electrons are outside this core Electrons are outside this core Most of the atom is empty space Most of the atom is empty space

Nuclear Particles 1. Protons Mass nearly equal to the H atom Mass nearly equal to the H atom Positive charge Positive charge 2. Neutrons Mass slightly greater than that of the proton Mass slightly greater than that of the proton No charge No charge

Mass and the Atom More than 99.9% of the atomic mass is concentrated in the nucleus More than 99.9% of the atomic mass is concentrated in the nucleus The volume of the nucleus is much smaller than the volume of the atom The volume of the nucleus is much smaller than the volume of the atom

Table 2.1 – Subatomic Particles

Terminology Atomic number, Z Atomic number, Z Number of protons in the atom Number of protons in the atom Mass number, A Mass number, A Number of protons plus number of neutrons Number of protons plus number of neutrons

Isotopes Isotopes are two atoms of the same element Isotopes are two atoms of the same element Same atomic number Same atomic number Different mass numbers Different mass numbers Number of neutrons is A minus Z Number of neutrons is A minus Z Number of neutrons differs between isotopes Number of neutrons differs between isotopes

Nuclear symbolism A is the mass number A is the mass number Z is the atomic number Z is the atomic number X is the chemical symbol X is the chemical symbol

The Chemists’ Shorthand: Atomic Symbols K  Element Symbol Mass number  Atomic number 

Two Isotopes of Sodium Copyright © Cengage Learning. All rights reserved

Atomic Masses: The Carbon-12 Scale The atomic mass of an element indicates how heavy, on average, an atom of an element is when compared to an atom of another element The atomic mass of an element indicates how heavy, on average, an atom of an element is when compared to an atom of another element Unit is the atomic mass unit (amu) Unit is the atomic mass unit (amu) Mass of one 12 C atom = 12 amu (exactly) Mass of one 12 C atom = 12 amu (exactly) Note that 12 C and C-12 mean the same thing Note that 12 C and C-12 mean the same thing

Determining Atomic Masses Atomic masses can be determined to highly precise values by using a mass spectrometer Atomic masses can be determined to highly precise values by using a mass spectrometer The mass spectrometer separates matter based on its mass and charge The mass spectrometer separates matter based on its mass and charge The resulting data is plotted with abundance on the y-axis and mass on the x-axis The resulting data is plotted with abundance on the y-axis and mass on the x-axis

Figure 2.6: The Mass Spectrometer

Carbon 12 C has a mass of exactly amu 12 C has a mass of exactly amu Carbon in the periodic table has a mass of amu Carbon in the periodic table has a mass of amu Why isn’t it exactly ? Why isn’t it exactly ? Why are most atomic masses not whole numbers? Why are most atomic masses not whole numbers?

Isotopic Abundance To determine the mass of an element, we must know the mass of each isotope and the atom percent of the isotopes (isotopic abundance) To determine the mass of an element, we must know the mass of each isotope and the atom percent of the isotopes (isotopic abundance) The mass spectrometer can determine the isotopic abundance The mass spectrometer can determine the isotopic abundance

Chlorine There are two isotopes of chlorine There are two isotopes of chlorine Atomic mass Abundance Cl amu 75.53% Cl amu 24.47%

Weighted Averages For an element with two isotopes, Y 1 and Y 2 : For an element with two isotopes, Y 1 and Y 2 : For chlorine: For chlorine:

Example 2.2

Example 2.2, (Cont’d)

Relative Atomic Masses The mass of an element is indicated below the symbol for the element The mass of an element is indicated below the symbol for the element Consider He Consider He On average, one He atom weighs amu On average, one He atom weighs amu This is about 1/3 the mass of a carbon-12 atom This is about 1/3 the mass of a carbon-12 atom

Masses of Individual Atoms For many purposes, relative masses are not sufficient For many purposes, relative masses are not sufficient It is necessary to know the mass of an atom in grams so the quantity of matter can be determined by weighing It is necessary to know the mass of an atom in grams so the quantity of matter can be determined by weighing The number that converts the mass of an atom in atomic mass units to the mass of a collection of atoms in grams is called Avogadro’s Number The number that converts the mass of an atom in atomic mass units to the mass of a collection of atoms in grams is called Avogadro’s Number

Masses of Atoms in Grams It is usually sufficient to know the relative masses of atoms It is usually sufficient to know the relative masses of atoms One He atom is about four times as heavy as one H atom One He atom is about four times as heavy as one H atom Therefore Therefore The mass of 100 He atoms is about four times the mass of 100 H atoms The mass of 100 He atoms is about four times the mass of 100 H atoms The mass of a million He atoms is about four times the mass of a million H atoms The mass of a million He atoms is about four times the mass of a million H atoms

Example 2.3

Example 2.3, (Cont’d)

Introduction to the Periodic Table

Periods and Groups Horizontal rows are periods Horizontal rows are periods First period is H and He First period is H and He Second period is Li-Ne Second period is Li-Ne Third period is Na-Ar Third period is Na-Ar Vertical columns are groups Vertical columns are groups IUPAC convention: use numbers 1-18 IUPAC convention: use numbers 1-18

Blocks in the Periodic Table Main group elements Main group elements 1, 2, , 2, Transition Transition Post-transition metals (aka Other Metals) Post-transition metals (aka Other Metals) Elements in groups to the right of the transition metals Elements in groups to the right of the transition metals Ga, In, Tl, Sn, Pb, Bi, Po Ga, In, Tl, Sn, Pb, Bi, Po

Families with Common Names Alkali Metals, Group 1 Alkali Metals, Group 1 Alkaline Earth Metals, Group 2 Alkaline Earth Metals, Group 2 Halogens, Group 17 Halogens, Group 17 Noble Gases, Group 18 Noble Gases, Group 18

Importance of Families (Groups) Elements within a family have similar chemical properties Elements within a family have similar chemical properties Alkali metals are all soft, reactive metals Alkali metals are all soft, reactive metals Noble gases are all relatively unreactive gases; He, Ne and Ar do not form compounds Noble gases are all relatively unreactive gases; He, Ne and Ar do not form compounds

Arrangement of Elements Periods Periods Arranged by increasing atomic number Arranged by increasing atomic number Families Families Arranged by chemical properties Arranged by chemical properties

Mendeleev Dmitri Mendeleev, Dmitri Mendeleev, Arranged elements by chemical properties Arranged elements by chemical properties Left spaces for elements yet unknown Left spaces for elements yet unknown Predicted detailed properties for elements as yet unknown Predicted detailed properties for elements as yet unknown Sc, Ga, Ge Sc, Ga, Ge By 1886, all these elements had been discovered, all with properties similar to those he predicted By 1886, all these elements had been discovered, all with properties similar to those he predicted

Metals and Nonmetals Diagonal line starting with B separates the metals from the nonmetals Diagonal line starting with B separates the metals from the nonmetals Elements along this diagonal have some of the properties of metals and some of the properties of nonmetals Elements along this diagonal have some of the properties of metals and some of the properties of nonmetals Metalloids Metalloids B, Si, Ge, As, Sb, Te B, Si, Ge, As, Sb, Te

Figure 2.9 – Biologically Important and Toxic Elements

Molecules Two or more atoms may combine to form a molecule Two or more atoms may combine to form a molecule Atoms involved are often nonmetals Atoms involved are often nonmetals Covalent bonds are strong forces that hold the atoms together Covalent bonds are strong forces that hold the atoms together Molecular formulas Molecular formulas Number of each atom is indicated by a subscript Number of each atom is indicated by a subscript Examples Examples Water, H 2 O Water, H 2 O Ammonia, NH 3 Ammonia, NH 3

Structural Formulas Structural formulas show the bonding patterns within the molecule Structural formulas show the bonding patterns within the molecule

Example 2.4

Molecular Elements Some elements exist as molecules, including such common ones as oxygen, hydrogen and nitrogen Some elements exist as molecules, including such common ones as oxygen, hydrogen and nitrogen

Ions When atoms or molecules lose or gain electrons, they form charged particles called ions When atoms or molecules lose or gain electrons, they form charged particles called ions Na → Na + + e - Na → Na + + e - O + 2e - → O 2- O + 2e - → O 2- Positively charged ions are called cations Positively charged ions are called cations Negatively charged ions are called anions Negatively charged ions are called anions There is no change in the number of protons in the nucleus when an ion forms. There is no change in the number of protons in the nucleus when an ion forms.

Example 2.5

Example 2.5 (Cont’d)

Polyatomic Ions Groups of atoms may carry a charge; these are the polyatomic ions Groups of atoms may carry a charge; these are the polyatomic ions OH -, hydroxide ion OH -, hydroxide ion NH 4 +, ammonium ion NH 4 +, ammonium ion

Compounds can form between anions and cations Compounds can form between anions and cations Sodium chloride, NaCl Sodium chloride, NaCl Sodium cations and chloride anions ions associate into a continuous network Sodium cations and chloride anions ions associate into a continuous network Ionic Compounds

Forces Between Ions Ionic compounds are held together by strong forces called ionic bonds Ionic compounds are held together by strong forces called ionic bonds Electrostatic attraction of + and – for each other Electrostatic attraction of + and – for each other Compounds are usually solids at room temperature Compounds are usually solids at room temperature High melting points High melting points May be water-soluble May be water-soluble

Solutions of Ionic Compounds When an ionic compound dissolves in water, the ions are released from each other When an ionic compound dissolves in water, the ions are released from each other Presence of ions in the solution leads to electrical conductivity Presence of ions in the solution leads to electrical conductivity Strong electrolytes Strong electrolytes When molecular compounds dissolve in water, no ions are formed When molecular compounds dissolve in water, no ions are formed Without ions, solution does not conduct electricity Without ions, solution does not conduct electricity Nonelectrolytes Nonelectrolytes

Formulas of Ionic Compounds Charge balance Charge balance Each positive charge must have a negative charge to balance it Each positive charge must have a negative charge to balance it Calcium chloride, CaCl 2 Calcium chloride, CaCl 2 Ca 2+ Ca 2+ Two Cl - ions are required for charge balance Two Cl - ions are required for charge balance

Predicting Charges on Monatomic Ions KNOW THESE !!!! Cd +2

The Other Metals All other metals can have various positive charges from +1 to +7 All other metals can have various positive charges from +1 to +7 Roman Numerals are used to tell the charge Roman Numerals are used to tell the charge

Monatomic Ions

Flow Chart for Naming Ionic Compounds

Naming Postive Ions With group 1, 2, Al, Zn, Cd, and Ag you just give the name of the atom With group 1, 2, Al, Zn, Cd, and Ag you just give the name of the atom Na + is Sodium Na + is Sodium Mg +2 is Magnesium Mg +2 is Magnesium Ag + is Silver Ag + is Silver Al +3 is Aluminum Al +3 is Aluminum

All the other metals With all other metals you give the name Metal followed by a roman numerial With all other metals you give the name Metal followed by a roman numerial Cu + - Copper (I) Cu + - Copper (I) Cu +2 – Copper (II) Cu +2 – Copper (II) Fe +2 – Iron (II) Fe +2 – Iron (II) Fe +3 – Iron (III) Fe +3 – Iron (III) U +6 – Uranium (VI) U +6 – Uranium (VI)

Naming negative ions All negative ions have their endings changed to –ide All negative ions have their endings changed to –ide Oxygen becomes oxide Oxygen becomes oxide Fluorine becomes Fluoride Fluorine becomes Fluoride Nitrogen becomes Nitride Nitrogen becomes Nitride Chlorine becomes Chloride Chlorine becomes Chloride

Formulas of Ionic Compounds Formulas of ionic compounds are determined from the charges on the ions atoms ions atoms ions     –     – Na  +  F :  Na + : F :  NaF         sodium + fluorine sodium fluoride formula Charge balance: = 0 Charge balance: = 0

Writing a Formula Write the formula for the ionic compound that will form between Ba 2+ and Cl . To cancel out Ba’s +2, then two -1 Cl’s are needed. Solution: 1. Balance charge with + and – ions 2. Write the positive ion of metal first, and the negative ion Ba 2+ Cl  Cl  negative ion Ba 2+ Cl  Cl  3. Write the number of ions needed as subscripts BaCl 2 subscripts BaCl 2

Balancing a formula by math Every ionic compound should have a formula that has a charge that equals zero. Every ionic compound should have a formula that has a charge that equals zero. Barium Fluoride Barium Fluoride Ba +2 F - Ba +2 F - How many F’s are needed to balance Ba +2 ? How many F’s are needed to balance Ba +2 ? Two Two Formula is BaF 2 Formula is BaF 2

Another way – Drop, Swap, Reduce Aluminum Oxide Aluminum Oxide Al is always +3 Al is always +3 Oxide is always -2 Oxide is always -2 Al +3, O -2 Al +3, O -2 DROP: Al 3 O 2 DROP: Al 3 O 2 SWAP: Al 2 O 3 SWAP: Al 2 O 3 REDUCE: 2 and 3 are lowest integers, so leave alone REDUCE: 2 and 3 are lowest integers, so leave alone

Another example Magnesium Oxide Magnesium Oxide Mg is +2 Mg is +2 Oxide is -2 Oxide is -2 Mg +2, O -2 Mg +2, O -2 DROP: Mg 2 O 2 DROP: Mg 2 O 2 SWAP: Mg 2 O 2 SWAP: Mg 2 O 2 REDUCE: MgO, 2 and 2 divide each other out. REDUCE: MgO, 2 and 2 divide each other out.

Naming Compounds Binary Ionic Compounds: 1. Cation first, then anion 1. Cation first, then anion 2. Monatomic cation = name of the element 2. Monatomic cation = name of the element Ca 2+ = calcium ion Ca 2+ = calcium ion 3. Monatomic anion = root + -ide 3. Monatomic anion = root + -ide Cl  = chloride Cl  = chloride CaCl 2 = calcium chloride CaCl 2 = calcium chloride

Naming Binary Ionic Compounds Examples: Examples:NaCl ZnI 2 Al 2 O 3 sodium chloride zinc iodide aluminum oxide

Transition Metals Elements that can have more than one possible charge MUST have a Roman Numeral to indicate the charge on the individual ion. 1+ or or 3+ Cu +, Cu 2+ Fe 2+, Fe 3+ copper(I) ion iron(II) ion copper (II) ion iron(III) ion

Names of Variable Ions These elements REQUIRE Roman Numerals because they can have more than one possible charge: anything except Group 1A, 2A, Ag, Zn, Cd, and Al (You should already know the charges on these!) Or another way to say it is: Transition metals and the metals in groups 4A and 5A (except Ag, Zn, Cd, and Al) require a Roman Numeral. FeCl 3 (Fe 3+ ) iron (III) chloride CuCl (Cu + ) copper (I) chloride SnF 4 (Sn 4+ ) tin (IV) fluoride PbCl 2 (Pb 2+ )lead (II) chloride Fe 2 S 3 (Fe 3+ )iron (III) sulfide Fe 2 S 3 (Fe 3+ )iron (III) sulfide

Examples of Older Names of Cations formed from Transition Metals (you do not have to memorize these)

Formulas and names Nitrate = NO 3 - Nitrate = NO 3 - Sulfate = SO 4 -2 Sulfate = SO 4 -2 Silver nitrate Silver nitrate Ag + NO 3 - Ag + NO 3 - DSR = AgNO 3 DSR = AgNO 3 Copper (I) Sulfate Copper (I) Sulfate Cu + SO 4 -2 Cu + SO 4 -2 Cu 2 SO 4 Cu 2 SO 4

More Polyatomics Lead (IV) Phosphate Lead (IV) Phosphate Pb +4 PO 4 -3 Pb +4 PO 4 -3 Pb 3 (PO 4 ) 4 Pb 3 (PO 4 ) 4 Notice: When more then one Polyatomic is present you surround it with () Notice: When more then one Polyatomic is present you surround it with () Big: The subscripts on Polyatomic ions are NEVER changed. Big: The subscripts on Polyatomic ions are NEVER changed.

More on Polyatomics Most polyatomic ions end in –ate. Most polyatomic ions end in –ate. The ending –ite means one less oxygen is present then in the ending –ate. The ending –ite means one less oxygen is present then in the ending –ate. Example: Nitrate versus Nitrite: Example: Nitrate versus Nitrite: NO 3 - NO 2 - NO 3 - NO 2 - NOTICE: Only the number of O’s changed, not the charge. NOTICE: Only the number of O’s changed, not the charge.

Even More The Prefix Hypo means two less oxygen’s are present then in –ate. The Prefix Hypo means two less oxygen’s are present then in –ate. Example: Hyposulfite:SO 2 -2 Example: Hyposulfite:SO 2 -2 The Prefix Per- means one extra oxygen is present then in –ate. The Prefix Per- means one extra oxygen is present then in –ate. Examples: Examples: PerchlorateClO 4 - PerchlorateClO 4 - ChlorateClO 3 - ChlorateClO 3 - ChloriteClO 2 - ChloriteClO 2 - HypoChloriteClO - HypoChloriteClO -

What if Hydrogen is in it? The Prefix Bi means that a Hydrogen is added, and the charge is reduced by one. The Prefix Bi means that a Hydrogen is added, and the charge is reduced by one. Example: Example: BiCarbonateHCO 3 -1 BiCarbonateHCO 3 -1 May also go by Hydrogen Carbonate. May also go by Hydrogen Carbonate.

Ionic Compounds Have to know what ions they form off table, polyatomic, or figure it out Have to know what ions they form off table, polyatomic, or figure it out CaS CaS K 2 S K 2 S AlPO 4 AlPO 4 K 2 SO 4 K 2 SO 4 FeS FeS CoI 3 CoI 3

Ionic Compounds Sodium sulfite Sodium sulfite calcium iodide calcium iodide Lead (II) oxide Lead (II) oxide Lead (IV) oxide Lead (IV) oxide Mercury (I) sulfide Mercury (I) sulfide Barium chromate Barium chromate Aluminum hydrogen sulfate Aluminum hydrogen sulfate Cerium (IV) nitrite Cerium (IV) nitrite

Naming Covalent Compounds Two words, with prefixes Two words, with prefixes Prefixes tell you how many. Prefixes tell you how many. mono, di, tri, tetra, penta, hexa, septa, nona, deca mono, di, tri, tetra, penta, hexa, septa, nona, deca First element whole name with the appropriate prefix, except mono First element whole name with the appropriate prefix, except mono Second element, -ide ending with appropriate prefix Second element, -ide ending with appropriate prefix

Covalent compounds The name tells you how to write the formula The name tells you how to write the formula duh duh Sulfur dioxide Sulfur dioxide diflourine monoxide diflourine monoxide nitrogen trichloride nitrogen trichloride diphosphorus pentoxide diphosphorus pentoxide

CO 2 CO 2 CO CO CCl 4 CCl 4 N 2 O 4 N 2 O 4 XeF 6 XeF 6 N 4 O 4 N 4 O 4 P 2 O 10 P 2 O 10 Naming Covalent Compounds

Covalent compounds The name tells you how to write the formula The name tells you how to write the formula Sulfur dioxide Sulfur dioxide diflourine monoxide diflourine monoxide nitrogen trichloride nitrogen trichloride diphosphorus pentoxide diphosphorus pentoxide

Acids Substances that produce H + ions when dissolved in water. Substances that produce H + ions when dissolved in water. All acids begin with H. All acids begin with H. Two types of acids: Two types of acids: Oxyacids Oxyacids Non-oxyacids Non-oxyacids

Naming acids If the formula has oxygen in it If the formula has oxygen in it write the name of the anion, but change write the name of the anion, but change ate to -ic acid ate to -ic acid ite to -ous acid ite to -ous acid Watch out for sulfuric and sulfurous Watch out for sulfuric and sulfurous H 2 CrO 4 H 2 CrO 4 HMnO 4 HMnO 4 HNO 2 HNO 2

Naming acids If the acid doesn’t have oxygen If the acid doesn’t have oxygen add the prefix hydro- add the prefix hydro- change the suffix -ide to -ic acid change the suffix -ide to -ic acid HCl HCl H 2 S H 2 S HCN HCN

Formulas for acids Backwards from names. Backwards from names. If it has hydro- in the name it has no oxygen If it has hydro- in the name it has no oxygen Anion ends in -ide Anion ends in -ide No hydro, anion ends in -ate or -ite No hydro, anion ends in -ate or -ite Write anion and add enough H to balance the charges. Write anion and add enough H to balance the charges.

Formulas for acids hydrofluoric acid hydrofluoric acid dichromic acid dichromic acid carbonic acid carbonic acid hydrophosphoric acid hydrophosphoric acid hypofluorous acid hypofluorous acid perchloric acid perchloric acid phosphorous acid phosphorous acid