Chapter 2 Atoms, Molecules and Ions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 2 (p.49-68) Atomic number, mass number and isotopes. The periodic table. Molecules and ions. Chemical formulas. Naming compounds. Tables – 2.3 – – 2.6 – 2.7 Examples – 2.3 – 2.4 – 2.5 – 2.6 – 2.7 – 2.8 – 2.9

mass p = mass n = 1840 x mass e - 2.2

Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) ; the same atomic number, with different numbers of neutrons in their nuclei X A Z H 1 1 H (D) 2 1 H (T) 3 1 U U Mass Number Atomic Number Element Symbol 2.3 Atomic number, Mass number and Isotopes

2.3 The Isotopes of Hydrogen

6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons Do You Understand Isotopes? 2.3 How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ?

Chemistry In Action Natural abundance of elements in Earth’s crust Natural abundance of elements in human body 2.4

The monatomic molecules are the single atoms of noble gases; He, Ne, Ar, Kr, Xe, Rn. A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces. H2H2 H2OH2ONH 3 CH 4 A diatomic molecule contains only two atoms H 2, N 2, O 2, Br 2, HCl, CO A polyatomic molecule contains more than two atoms O 3, H 2 O, NH 3, CH Allotrope is one of tow or more distinct forms of an element as O 2, O 3.

An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons 2.5

A monatomic ion contains only one atom A polyatomic ion contains more than one atom 2.5 Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- OH -, CN -, NH 4 +, NO 3 -

13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons Do You Understand Ions? 2.5 How many protons and electrons are in ?Al How many protons and electrons are in ?Se

2.6

2.5 الأيونات Ions

Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal 2.4 Periodic table is a chart in which elements having similar chemical and physical properties are grouped together in this table the elements are arranged by atomic number.

A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance An empirical formula shows the simplest whole-number ratio of the atoms in a substance H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH 2 2.6

A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance An empirical formula shows the simplest whole-number ratio of the atoms in a substance CH C2H2C2H2 molecularempirical C 8 H 10 N 4 O 2 C4H5N2OC4H5N2O S8S8 S N2ON2ON2ON2O 2.6

ionic compounds consist of a combination of cations and an anions the formula is always the same as the empirical formula the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl 2.6

Formula of Ionic Compounds Al 2 O x +3 = +63 x -2 = -6 Al 3+ O 2- CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br - Na 2 CO 3 2 x +1 = +21 x -2 = -2 Na + CO 3 2-

1. An anion is defined as A.a charged atom or group of atoms with a net negative charge. B.a stable atom. C.a group of stable atoms. D.an atom or group of atoms with a net positive charge. 2. Atoms of the same element with different mass numbers are called A.ions. B.neutrons. C.allotropes. D.chemical families. E.isotopes. 3. How many neutrons are there in an atom of lead whose mass number is 208? A.82 B.126 C.208 D.290 E.none of them

4. An atom of the isotope sulfur-31 consists of how many protons, neutrons, and electrons? (p = proton, n = neutron, e = electron) A.15 p, 16 n, 15 e B.16 p, 15 n, 16 e C.16 p, 31 n, 16 e D.32 p, 31 n, 32 e E.16 p, 16 n, 15 e 5. A magnesium ion, Mg 2+, has A.12 protons and 13 electrons. B.24 protons and 26 electrons. C.12 protons and 10 electrons. D.24 protons and 22 electrons. E.12 protons and 14 electrons. 6. A sulfide ion, S 2-, has: A.16 protons and 16 electrons B.32 protons and 16 electrons C.16 protons and 14 electrons D.16 protons and 18 electrons E.32 protons and 18 electrons

7.Which compound has the same empirical formula as C 6 H 12 O 6 ? A)C 12 H 24 O 12 B)C3H3O3C3H3O3 C)CH 2 ON D)CHO 2 8.Which one of the following represented three molecules ? A)3 O 3 B)O3O3 C)3 O D)H 2 O

Answer Key 1-A 2-E 3-B 4-B 5-C 6-D 7-A 8-A Problems 2.10 – 2.11 – 2.12 – 2.14 – 2.16 – – 2.36 – 2.44 – 2.46 – 2.50

Chemical Nomenclature Ionic Compounds –often a metal + nonmetal –First named the cation (metal) then the anion (nonmetal) by adding “ide” to the first part of the element name. Binary compounds are compounds formed from just two elements and ternary compounds are compounds formed from three elements. BaCl 2 barium chloride K2OK2Opotassium oxide Mg(OH) 2 magnesium hydroxide KSCN potassium thiocyanate 2.7

Transition metal ionic compounds –In the Stock system the different cations charge are designated with Roman numerals FeCl 2 2 Cl - -2 so Fe is +2 iron(II) chloride FeCl 3 3 Cl - -3 so Fe is +3 iron(III) chloride Cr 2 S 3 3 S so Cr is +3 (6/2) chromium(III) sulfide 2.7

Molecular compounds nonmetals or nonmetals + metalloids element further left in periodic table is 1 st element closest to bottom of group is 1 st common names H 2 O, NH 3, CH 4 The Greek prefixes was used to donate the number of atoms of each element in the molecular compounds The prefix “mono” may be omitted for the first element For oxides the ending “a” in the prefix is sometimes omitted. last element ends in ide 2.7

HIhydrogen iodide NF 3 nitrogen trifluoride SO 2 sulfur dioxide N2O4N2O4 dinitrogen tetroxide NO 2 nitrogen dioxide N2ON2Odinitrogen monoxide Molecular Compounds 2.7 TOXIC ! Laughing Gas

2.7

An acid can be defined as a substance that yields hydrogen ions (H + ) when dissolved in water. HCl Pure substance, hydrogen chloride Dissolved in water (H + Cl - ), hydrochloric acid An oxoacid is an acid that contains hydrogen, oxygen, and another element. HNO 3 nitric acid H 2 CO 3 carbonic acid H 2 SO 4 sulfuric acid 2.7 HNO 3 H 3 PO 4 phosphoric acid

2.7

A base can be defined as a substance that yields hydroxide ions (OH - ) when dissolved in water. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH) 2 barium hydroxide 2.7

Hydrates are compounds that have a specific number of water molecules attached to them. BaCl 2 2H 2 O 2.7 LiClH 2 O MgSO 4 7H 2 O Sr(NO 3 ) 2 4H 2 O barium chloride dihydrate lithium chloride monohydrate magnesium sulfate heptahydrate strontium nitrate tetrahydrate CuSO 4 5H2O CuSO4

2.7

Worked Example 2.9

9.Which of the following compounds is named lithium carbonate? A)Na 2 CO 3 B)LiHCO 3 C)LiCO D)Li 2 CO 3 10.What is the name of KClO? A)potassium chlorite B)potassium chloride C)potassium hypochlorite D)potassium oxide 11.What is the formula for ammonium sulfate? A)NH 4 SO 4 B)NH 4 (SO 4 ) 2 C)(NH 4 ) 2 SO 4 D)NH 4 S

Answer Key 9-D 10-C 11-C Problems 2.58 – 2.60 – 2.94