Chapter 2 Atoms, Molecules and Ions

Conservation of Mass and the Law of Definite Proportions Law of Conservation of Mass: Mass is neither created nor destroyed in chemical reactions. Aqueous solutions of mercury(II) nitrate and potassium iodide will react to form a precipitate of mercury(II) iodide and aqueous potassium iodide. Hg(NO 3 ) 2 (aq) + 2KI(aq)  HI 2 (s) + 2KNO 3 (aq) 4.55 g g = 6.57 g 3.25 g g = 6.57 g

Conservation of Mass and the Law of Definite Proportions Law of Definite Proportions: Different samples of a pure chemical substance always contain the same proportion of elements by mass. By mass, water is:88.8 % oxygen 11.2 % hydrogen

Dalton’s Atomic Theory and the Law of Multiple Proportions Elements are made up of tiny particles called atoms. Each element is characterized by the mass of its atoms. Atoms of the same element have the same mass, but atoms of different elements have different masses. Chemical combination of elements to make different substances occurs when atoms join together in small whole-number ratios. Chemical reactions only rearrange the way that atoms are combined; the atoms themselves don’t change.

Dalton’s Atomic Theory and the Law of Multiple Proportions Law of Multiple Proportions: Elements can combine in different ways to form different substances, whose mass ratios are small whole- number multiples of each other. nitric oxide: 8 grams oxygen per 7 grams nitrogen nitrous oxide: 16 grams oxygen per 7 grams nitrogen

Dalton’s Atomic Theory and the Law of Multiple Proportions

The Structure of Atoms: Electrons Cathode-Ray Tubes: J. J. Thomson ( ) proposed that cathode rays must consist of tiny negatively charged particles. We now call them electrons.

The Structure of Atoms: Protons and Neutrons Atomic Nucleus: Ernest Rutherford ( ) bombarded gold foil with alpha particles. Although most of the alpha particles passed through the foil undeflected, approximately 1 in every 20,000 particles were deflected. A fraction of those particles were deflected back at an extreme angle. Rutherford proposed that the atom must consist mainly of empty space with the mass concentrated in a tiny central core—the nucleus.

The Structure of Atoms: Protons and Neutrons

The charge of the proton is opposite in sign but equal to that of the electron

Atomic Number Atomic Number (Z): Number of protons in an atom’s nucleus. Equivalent to the number of electrons around the atom’s nucleus. Mass Number (A): The sum of the number of protons and the number of neutrons in an atom’s nucleus. Isotope: Atoms with identical atomic numbers but different mass numbers.

Atomic Number carbon-14 C 14 6 atomic number mass number carbon-12 C 12 6 atomic number mass number 6 protons 6 electrons 8 neutrons 6 protons 6 electrons 6 neutrons

Examples Write the symbol for the magnesium atom (atomic number 12) with a mass number of 24. How many electrons and how many neutrons does this atom have? Write the symbol for the magnesium atom (atomic number 12) with a mass number of 24. How many electrons and how many neutrons does this atom have? Write the symbol for the silver atom (Z = 47) that has 61 neutrons Write the symbol for the silver atom (Z = 47) that has 61 neutrons The krypton atom has 48 neutron The krypton atom has 48 neutron

Example Given the number of protons, neutrons and electrons in the following atom Given the number of protons, neutrons and electrons in the following atom Co Co Cl Cl Hg Hg

Atomic Mass The mass of 1 atom of carbon-12 is defined to be 12 amu Atomic Mass: The weighted average of the isotopic masses of the element’s naturally occurring isotopes.

Atomic Mass Why is the atomic mass of the element carbon amu? carbon-12:98.89 % natural abundance12 amu carbon-13:1.11 % natural abundance amu mass of carbon = (12 amu)(0.9889) + ( amu)(0.0111) amu = amu amu

Examples Chlorine has two naturally occuring isotopes: Cl-35 with a naturally abundance of 75.77% and an isotopic mass of amu, and Cl-37 with the naturally abudance of 24.23% and an isotopic mass amu. What is the atomic mass of chlorine? Chlorine has two naturally occuring isotopes: Cl-35 with a naturally abundance of 75.77% and an isotopic mass of amu, and Cl-37 with the naturally abudance of 24.23% and an isotopic mass amu. What is the atomic mass of chlorine?

Compounds and Mixtures

Variable properties Similar properties

Compounds and Mixtures Cannot be separated physically The same number of protons

Molecules, Ions, and Chemical Bonds Covalent Bond: Results when two atoms share several (usually two) electrons. Typically a nonmetal bonded to a nonmetal.

Molecules, Ions, and Chemical Bonds Ionic Bond: A transfer of one or more electrons from one atom to another. An electrostatic attraction between charged particles.Typically a metal bonded to a nonmetal. Ion: A charged particle. Cation: A positively charged particle. Metals tend to form cations. Anion: A negatively charged particle. Nonmetals tend to form anions.

Molecules, Ions, and Chemical Bonds In the formation of sodium chloride, one electron is transferred from the sodium atom to the chlorine atom. Na 1+ + Cl 1- Na + Cl 11 protons 10 electrons 17 protons 18 electrons 11 protons 11 electrons 17 protons 17 electrons

Molecules, Ions, and Chemical Bonds

Acids and Bases Acid: A substance that provides H1+ ions in water. HCl, HNO 3, H 2 SO 4, H 3 PO 4 Turns litmus red. Base: A substance that provides OH1- ions in water. NaOH, KOH, Ba(OH) 2 Turns litmus blue.

Acids H 2 O(l) HCl(aq) H + (aq) + Cl - (aq) HCl(aq) H + (aq) + Cl - (aq) H 2 O(l) HNO 3 H + (aq) + NO 3 - (aq) HNO 3 H + (aq) + NO 3 - (aq) H 2 O(l) H2SO4(aq) H + (aq) + HSO 4 - (aq) H2SO4(aq) H + (aq) + HSO 4 - (aq) H 2 O(l) HSO 4 - (aq) H + (aq) + SO 4 - (aq) HSO 4 - (aq) H + (aq) + SO 4 - (aq)

Bases H 2 O(l) NaOH(s) Na + (aq) + - OH(aq) NaOH(s) Na + (aq) + - OH(aq) H 2 O(l) Ba(OH) 2 (aq)Ba 2+ (aq) OH(aq) Ba(OH) 2 (aq)Ba 2+ (aq) OH(aq)

Binary Ionic compound Binary Ionic Compounds Binary Ionic Compounds Ionic compound ( contain a cation and anion) containing only two element Ionic compound ( contain a cation and anion) containing only two element The charge on the ion depends on the group number The charge on the ion depends on the group number

Charge Determination Main-group metal cations: charge = group number Group IA = +1 (M 1+ ) Group IIA = +2 (M 2+ ) Group IIIA = +3 (M 3+ ) Main group nonmetal anions: charge = group number - 8 E.g:Group VA = -3 Group VIA = -2 Group VIIA = -1

Naming Chemical Compounds

1- Naming Chemical Compounds Anion Charges for Typical Main-Group Ions 3-2-

Naming Chemical Compounds Ionic Compound: A neutral compound in which the total number of positive charges must equal the total number of negative charges. Electrical Neutrality – cations and anions combine in such a manner that the overall charge on the compound is equal to zero Total negative charge = total positive charge Formulas for ionic compounds always contain the smallest whole number ratio of cation to anion.

Examples Na + + Cl -  NaCl (+1) + (-1) = 0 K + + O 2-  K 2 O K + + K + + O 2-  K 2 O (+1) (+1) + (-2) = 0 Mg 2+ + N 3-  Mg 3 N 2

Rules for Naming Ionic Compound The cation is always named first and the anion second The cation is always named first and the anion second The name of cation stays the same The name of cation stays the same Na + = Sodium Na + = Sodium The name of anion takes the first part of the root name and adding –ide The name of anion takes the first part of the root name and adding –ide Cl- = Cloride Cl- = Cloride

Steps in naming a compound LiF LiF Step 1 Step 1 Identify the cations and anion (as well as the group number Identify the cations and anion (as well as the group number Step 2 Step 2 Name the cation Name the cation Step 3 Step 3 Name the anion Name the anion Step 4 Step 4 Name the compound by combining the names Name the compound by combining the names

Example Name each binary compound Name each binary compound AlCl 3 AlCl 3 SrS SrS BaH 2 BaH 2 MgO MgO Li 3 N Li 3 N

Naming Binary Ionic Compound Contains metals mostly from the transitional group Contains metals mostly from the transitional group Must use Roman numeral to indicate their charges Must use Roman numeral to indicate their charges E.g +2 = II +3 = III +4 = IV

Example Give the system of each of the following compounds Give the system of each of the following compounds PbCl 4 PbCl 4 CoCl 3 CoCl 3 Fe 2 S 3 Fe 2 S 3 CrI 3 CrI 3

5.3 Naming Binary Contain Only Nonmetals The first element in the formula is named first and the full element name is used The first element in the formula is named first and the full element name is used The second element is named as though it were an anion ( -ide ending) The second element is named as though it were an anion ( -ide ending) Prefixes is used to indicate the number of atoms present. (prefer to table 2.2) Prefixes is used to indicate the number of atoms present. (prefer to table 2.2) The prefix mono- is never used for naming the first element. The prefix mono- is never used for naming the first element.

Naming Chemical Compounds Molecular Compound (Molecule): The unit of matter that results when two or more atoms are joined by covalent bonds.

Naming Chemical Compounds N2F4N2F4 The second element listed is more anionlike and takes the name of the element with an “ide” modification to the ending. The first element listed is more cationlike and takes the name of the element. The prefix is added to the front of each to indicate the number of each atom. dinitrogen tetrafluoride

Example Name the following compound Name the following compound CCl 4 CCl 4 N 2 O 5 N 2 O 5 SiO 2 SiO 2 P 4 O 6 P 4 O 6 BrF 3 BrF 3

Naming Binary Compounds: a Review

5.5 Naming Compounds that Contain Polyatomic Ions Polyatomic ions – two or more nonmetals are covalently bonded and have charges Polyatomic ions – two or more nonmetals are covalently bonded and have charges Can be positively charge or negatively charge Can be positively charge or negatively charge Oxyanion – nonmetal is bonded to an oxygen element and carried a negative charge Oxyanion – nonmetal is bonded to an oxygen element and carried a negative charge

Naming Chemical Compounds

Polyatomic Ionic Compounds sodium carbonate:Na 2 CO 3 Na 1+ CO 3 2- iron(II) hydroxide:Fe(OH) 2 Fe 2+ OH 1- magnesium carbonate:MgCO 3 Mg 2+ CO 3 2- sodium hydroxide:NaOHNa 1+ OH 1-

Example Name the following compounds Name the following compounds Na 2 CO 3 Na 2 CO 3 CsClO 3 CsClO 3 Fe(OH) 2 Fe(OH) 2 Ca(HCO 3 ) 2 Ca(HCO 3 ) 2

Naming Acids Acids – substance that produces H+ when dissolve in water Acids – substance that produces H+ when dissolve in water Prefix hydro is used when the anion does not contain oxygen and the suffix –ic is attached to the root name of element Prefix hydro is used when the anion does not contain oxygen and the suffix –ic is attached to the root name of element When the anion contains oxygen, the acid name is formed from the root name of the central element of the anion or the anion name, with a suffix of –ic or -ous When the anion contains oxygen, the acid name is formed from the root name of the central element of the anion or the anion name, with a suffix of –ic or -ous

Naming Chemical Compounds “ate”“ic” “ite”“ous”

Flow Chart Prefix hydro: no oxgen Prefix hydro: no oxgen -ate  ic acid -ite  ous acid

Example Name the following acids Name the following acids HCl HCl HF HF HBrO 4 HBrO 4 H 2 SO 4 H 2 SO 4 HCN HCN

Writing Formulas from Name Provide the correct formula for the following compounds Provide the correct formula for the following compounds Potassium hydroxide Potassium hydroxide Lead(IV) oxide Lead(IV) oxide Sodium nitrate Sodium nitrate Carbon disulfide Carbon disulfide Hydrobromic acid Hydrobromic acid Hypoiodous acid Hypoiodous acid