Atoms, Molecules and Ions

Atoms, Molecules and Ions

Atoms, Molecules and Ions 2 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atomic structure mass p mass n 1840 x mass e3 Atomic number, Mass number and Isotopes 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) with different numbers of neutrons in their nuclei

Mass Number A ZX Atomic Number 1 1H H isotopes names: hydrogen tritium 235 92

2 1H U Element Symbol (D) deuterium 238 92

3 1H U (T) 4 Atomic number, Mass number and Isotopes The Isotopes of Hydrogen hydrogen tritium deuterium

5 Atomic number, Mass number and Isotopes How many protons, neutrons, and electrons are 14 in 6 C ? 6 protons, 8 (14 - 6) neutrons, 6 electrons How many protons, neutrons, and electrons are 11 in 6 C ?

6 protons, 5 (11 - 6) neutrons, 6 electrons 6 Atomic number, Mass number and Isotopes Find number of electrons, protons, and neutrons? 63 29 Cu 239 Pu 94

26 Al 13 17 8 O 202 8 Hg

48 Ti 22 e 29 94 13 8

80 22 p 29 94 13 8

80 22 n 34 145 13 9 122

26 Atomic number, Mass number and Isotopes 8 The Modern Periodic Table of elements discovered between (1800-1900) Only noble gases exists as single atoms called monoatomic 9 Noble Gas

Halogen Group Alkali Earth Metal Alkali Metal Period Group : similar chemical properties Period : increasing Z metals

Metals metalloids nonmetals -good conductors of heat and electricity -occupy most of the table Nonmetals -good conductors of heat and electricity -only 17 elements METALLOIDS - INTERMEDIATE BETWEEN METALS AND NON METALS

-ONLY 8 ELEMENTS Molecules and Ions A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces H2 H2O NH3 CH4 A diatomic molecule contains only two atoms

H2, N2, O2, Br2, HCl, CO diatomic elements A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4 11 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. Na

11 protons 11 electrons Na + 11 protons 10 electrons anion ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Cl

17 protons 17 electrons Cl - 17 protons 18 electrons 12 A monatomic ion contains only one atom Na+, Cl-, Ca2+, O2-, Al3+, N3A polyatomic ion contains more than one atom OH-, CN-, NH4+, NO3-

13 How many protons and electrons are in 27 3+ 13 Al ? 13 protons, 10 (13 3) electrons How many protons and electrons are in 78 2Se ?

34 34 protons, 36 (34 + 2) electrons 14 Chemical Formulas 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 molecular empirical

H2O H2O C6H12O6 CH2O O3 O N2H4

NH2 15 ionic compounds consist of a combination of cations and an anions The formula is usually 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 16 The most reactive metals (green) and the most reactive

nonmetals (blue) combine to form ionic compounds. 17 o If the charges on the cation and anion are numerically different, we apply the following rule to make the formula electrically neutral: The subscript of the cation is numerically equal to the charge on the anion, and the subscript of the anion is numerically equal to the charge on the cation. Aluminum Oxide. The cation is Al3+ and the oxygen anion is O2-. The sum of the charges is 2(+3) + 3(-2) = 0. Thus, the formula for aluminum oxide is

Formula of Ionic Compounds 2 x +3 = +6 Al 3 x -2 = -6 Al2O3 3+ O 1 x +2 = +2

Ca - Br 2 x +1= +2 Na 2 x -1 = -2 CaBr2 2+

+ 2- 1 x -2 = -2 Na2CO3 2- CO3 Common Ions Shown on the Periodic Table

20 Naming Compound Ionic Compounds Often a metal + nonmetal Anion (nonmetal), add ide to element name BaCl2 barium chloride K2 O potassium oxide Mg(OH)2

magnesium hydroxide KNO3 potassium nitrate 21 22 Transition metal ionic compounds indicate charge on metal with Roman numerals FeCl2

2 Cl- -2 so Fe is +2 iron(II) chloride FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide 23

If transition metals can form more tha one type of cations we use (ic ) for higher charge and (-ous ) for lower charge . FeCl2 iron(II) chloride becomes ferrous chloride FeCl3 iron(III) chloride becomes ferric chloride CuCl cupper(I) chloride becomes cupperous chloride CuCl2 cupper(II) chloride becomes cupperic chloride 25 26 27

Molecular compounds They are usually composed of nonmetallic elements. Many molecular compounds are binary compounds. Naming binary molecular compounds is similar to naming binary ionic compounds. We place the name of the first element in the formula first, and the second element is named by adding ide to the root of the element name. HCl hydrogen chloride HBr hydrogen bromide

SiC silicon carbide If a pair of elements form more than one compound, use prefixes to indicate number of each kind of atom Notes in naming compounds with prefixes: The prefix mono- may be omitted for the first element. For example, PCl3 is named phosphorus trichloride,

not monophosphorus trichloride. For oxides, the ending a in the prefix is sometimes omitted. For example, N2O4 may be called dinitrogen tetroxide rather than dinitrogen tetraoxide. Name the following compounds? HI hydrogen iodide NF3

nitrogen trifluoride SO2 sulfur dioxide N2Cl4 dinitrogen tetrachloride NO2 nitrogen dioxide N2O

dinitrogen monoxide 30 31 32 Acids An acid can be defined as a substance that yields hydrogen ions (H+) when dissolved in water. For example: HCl gas and HCl in water Pure substance, hydrogen chloride Dissolved in water (H O+ and Cl), 3

hydrochloric acid Anions whose names end in -ide form acids with a hydro- prefix and an -ic ending. HCl HCl hydrogen chloride hydrochloric acid Some Examples of acids Naming Oxoacids and Oxoanions An oxoacid is an acid that contains hydrogen, oxygen, and another element. phosphoric acid

carbonic acid nitric acid The formulas of oxoacids are usually written with the H first, followed by the central element and then O. H2CO3 (carbonic acid), HClO3 (chloric acid), HNO3 (nitric acid), H3PO4 (phosphoric acid), H2SO4 (sulfuric acid) 35 Two or more oxoacids have the same central atom but a different number of O atoms; the following rules to name these compounds. 1. Addition of one O atom to the -ic acid: The acid is

called per . . -ic acid. ( --ate) HClO3 chloric acid HClO4 perchloric acid 2. Removal of one O atom from the -ic acid: The acid is called -ous acid. ( --ite) HNO3 nitric acid HNO2 nitrous acid 3. Removal of two O atoms from the -ic acid: The acid is called hypo . . . -ous acid. HBrO3 Bromic acid

HBrO hypobromous acid. o The rules for naming oxoanions, anions of oxoacids, are as follows: 1. When all the H ions are removed from the -ic acid, the anions name ends with -ate. 2. When all the H ions are removed from the -ous acid, the anions name ends with -ite. 3. The names of anions in which one or more but not all the hydrogen ions have been removed must indicate the number of H ions present. For example: phosphoric acid H3PO4

H2PO4- dihydrogen phosphate HPO4 2- hydrogen phosphate PO43- phosphate parent acid for all halogenic acids is HXO3 Halogenicic acid

39 40 Bases 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 41 Hydrated compounds Hydrates are compounds that have a specific number of water molecules attached to them. BaCl22H2O barium chloride dihydrate LiClH2O

lithium chloride monohydrate MgSO47H2O magnesium sulfate heptahydrate Sr(NO3)2 4H2O strontium nitrate tetrahydrate CuSO45H2O CuSO4 42

43

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