Chapter 2 Atoms, Molecules, and Ions © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Dalton's Postulates Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Dalton's Postulates Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Subatomic Particles Protons and electrons are the only particles that have a charge. Protons and neutrons have essentially the same mass. The mass of an electron is so small we ignore it. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Symbols of Elements Elements are symbolized by one or two letters. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Symbols of Elements All atoms of the same element have the same number of protons, which is called the atomic number, Z. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Symbols of Elements The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Isotopes Isotopes are atoms of the same element with different masses. Isotopes have different numbers of neutrons. © 2012 Pearson Education, Inc.

Key Points The elements of The Periodic Table are classified into three groups – metals, nonmetals, and metalloids Elements in a group have similar chemical properties Elements in a in a period have different chemical properties

Metals, metalloids, and nonmetals. Figure 2.11 Metals, metalloids, and nonmetals. Cadmium Copper Lead Chromium Bismuth Arsenic Chlorine Silicon Antimony Bromine Sulfur Iodine Carbon (graphite) Boron Tellurium

The modern periodic table. Noble Gases Alkali metals Halogens Alkaline earth metals Transition Metals

The modern periodic table. Figure 2.10 The modern periodic table. +1 +2 +3 NC -3 -2 -1 12

© 2012 Pearson Education, Inc. Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound. © 2012 Pearson Education, Inc.

Diatomic Molecules These seven elements occur naturally as molecules containing two atoms: Hydrogen Nitrogen Oxygen Fluorine Chlorine Bromine Iodine © 2012 Pearson Education, Inc.

Chemical Formulas Molecular Formula Empirical Formula It only shows the exact number of atoms of each element in the smallest possible units of a substance Ex. H2O, O2, N2 Empirical Formula Tells us what elements are present and the simplest whole number ratio of their atoms Not necessarily the actual number of atoms in a given molecule. N2H4 molecular formula NH2 empirical formula

© 2012 Pearson Education, Inc. Ionic compounds (such as NaCl) are generally formed between metals and nonmetals. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Chemical Formulas Molecular (covalent or binary) compounds are composed of molecules and almost always contain only nonmetals. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Ions When atoms lose or gain electrons, they become ions. Cations are positive and are formed by elements on the left side of the periodic chart (donate electrons to non- metals) Anions are negative and are formed by elements on the right side of the periodic chart (gain electrons from metals) © 2012 Pearson Education, Inc.

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 18 electrons Cl 17 protons 17 electrons 2.5

© 2012 Pearson Education, Inc. Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: The charge on the cation becomes the subscript on the anion. The charge on the anion becomes the subscript on the cation. If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor. © 2012 Pearson Education, Inc.

Predicting Ionic Charge The sum of the charges on the cation and the anion have to add up to zero, thus the compound is electronically neutral Ex Al2O3 Predicting Ionic Charge The number of electrons an atom loses or gains is related to its position on the periodic table.

Naming Ionic Compounds cont.. Certain Metals especially transition metals can form more than one type of cation We use the Stock System to name them Mn 2+ MnO (manganese (II) oxide) Mn 3+ Mn2O3 (manganese (III) oxide) Mn 4+ MnO2 (manganese (IV) oxide)

Naming Ionic Compounds cont.. Binary compounds: made from just 2 elements Cation (electron donating number fixed) is named first and the name of the element stays the same Cation (electron donating more than one) follow the mentioned above rules Anion (electron accepting) is named second and you add -ide Ex. Oxygen turns to Oxide Ex Nitrogen turns to Nitride

Naming Binary Ionic Compounds Sample Problem 2.5 Naming Binary Ionic Compounds PROBLEM: Name the ionic compound formed from the following pairs of elements: (a) magnesium and nitrogen (b) iodine and cadmium (c) strontium and fluorine (d) sulfur and cesium SOLUTION: (a) magnesium nitride (b) cadmium iodide (c) strontium fluoride (d) cesium sulfide 24

Determining Formulas of Binary Ionic Compounds Sample Problem 2.6 Determining Formulas of Binary Ionic Compounds PROBLEM: Write empirical formulas for the compounds named in Sample Problem 2.5. SOLUTION: (a) magnesium nitride Mg2+ and N3-; three Mg2+(6+) and two N3-(6-); Mg3N2 (b) cadmium iodide Cd2+ and I-; one Cd2+(2+) and two I-(2-); CdI2 (c) strontium fluoride Sr2+ and F-; one Sr2+(2+) and two F-(2-); SrF2 (d) cesium sulfide Cs+ and S2-; two Cs+(2+) and one S2- (2-); Cs2S 25

Naming Ionic Compounds cont.. Ternary Compounds: made up three elements If cation (electron donating) has a fixed number of electrons to give the name will stay the same and it is named first If the cation (electron donating) different number of electrons to give the name will stay the same but you will mention the number of electrons (roman numerals) that are being donating and it is still named first If the anion (electron accepting) 1 element then you will add –ide If the anion (electron accepting) more than one element refer to table 2.5 page 63, it is mentioned after the cation

Sample Problem 2.8 Determining Names and Formulas of Ionic Compounds Containing Polyatomic Ions PROBLEM: Give the systematic names or the formula or the formulas for the names of the following compounds: (a) Fe(ClO4)2 (b) sodium sulfite (c) Ba(OH)2 8H2O SOLUTION: (a) ClO4- is perchlorate; iron must have a 2+ charge. This is iron(II) perchlorate. (b) The anion sulfite is SO32- therefore you need 2 sodiums per sulfite. The formula is Na2SO3. (c) Hydroxide is OH- and barium is a 2+ ion. When water is included in the formula, we use the term “hydrate” and a prefix which indicates the number of waters. So it is barium hydroxide octahydrate. 27

Molecular Compounds They are usually composed of nonmetal elements The chemical bond that forms between the elements is called “covalent bond” Most of them are binary compounds Named in the same manner as ionic compounds

Naming Molecular Compounds The first name the element that is first in the formula, its name does not change The second element in the formula is named second and –ide is added HCl (hydrogen chloride) HBr (hydrogen bromide)

Nomenclature of Binary Compounds The less electronegative atom is usually listed first. A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however) . The ending on the more electronegative element is changed to -ide. CO2: carbon dioxide CCl4: carbon tetrachloride

Nomenclature of Binary Compounds If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one. N2O5: dinitrogen pentoxide © 2012 Pearson Education, Inc.

Patterns in Oxyanion Nomenclature When there are two oxyanions involving the same element: The one with fewer oxygens ends in -ite. The one with more oxygens ends in -ate. NO2− : nitrite; SO32− : sulfite NO3− : nitrate; SO42− : sulfate © 2012 Pearson Education, Inc.

Determining Names and Formulas of Binary Covalent Compounds Sample Problem 2.11 Determining Names and Formulas of Binary Covalent Compounds SOLUTION: PROBLEM: (a) What is the formula of carbon disulfide? (b) What is the name of PCl5? (c) Give the name and formula of the compound whose molecules each consist of two N atoms and four O atoms. (a) Carbon is C, sulfide is sulfur S and di-means 2 - CS2. (b) P is phosphorous, Cl is chloride, the prefix for 5 is penta-. Phosphorous pentachloride. (c) N is nitrogen and is in a lower group number than O (oxygen). Therefore the formula is N2O4 - dinitrogen tetraoxide. 33

Acids Acid: a substance that yields hydrogen ions (H +, equivalent to a proton) when dissolved in water Formulas for acids contain one or more hydrogen as well as an anionic group The name assigned to the compound depends on its physical state Anions whose names end in “ide” form acids with a “hydro” prefix and an “ic” ending HCl Hydrochloric acid

Naming Acids

Determining Names and Formulas of Anions and Acids Sample Problem 2.10 Determining Names and Formulas of Anions and Acids PROBLEM: Name the following anions and give the names and formulas of the acids derived from them: (a) Br - (b) IO3 - (c) CN - (d) SO4 2- (e) NO2 - SOLUTION: (a) The anion is bromide; the acid is hydrobromic acid, HBr. (b) The anion is iodate; the acid is iodic acid, HIO3. (c) The anion is cyanide; the acid is hydrocyanic acid, HCN. (d) The anion is sulfate; the acid is sulfuric acid, H2SO4. (e) The anion is nitrite; the acid is nitrous acid, HNO2. 36