Elements and Compounds Chapter 2 Elements and Compounds

Setting the Stage – Search for Water A key molecule we search for on other planets is water, as its presence suggests the possibility of life Water is only one example of matter (albeit an important one) Matter is anything that has mass and occupies space Chemistry is the study of matter and the changes that it undergoes Malone and Dolter - Basic Concepts of Chemistry 9e

Setting a Goal - Part A The Elements and Their Composition You will become familiar with the basic components of matter and the properties that make each type of matter unique Malone and Dolter - Basic Concepts of Chemistry 9e

Objectives for Section 2-1 Distinguish between elements and compounds Match the names and symbols of the common elements Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e 2-1 The Elements An element is the most basic form of matter that exists under ordinary circumstances A compound is a unique substance that is composed of two or more elements that are chemically combined Malone and Dolter - Basic Concepts of Chemistry 9e

Elements Free in Nature Only a few elements are found in their free state (not combined with other elements) Malone and Dolter - Basic Concepts of Chemistry 9e

Elemental Distribution The Earth has 88 elements present in measurable amounts, but 10 constitute ~98.9% of the crust There are 112+ known elements (26 spontaneously decay into other elements) The human body is 93% carbon, hydrogen and oxygen Malone and Dolter - Basic Concepts of Chemistry 9e

Distribution of Elements – the Earth Malone and Dolter - Basic Concepts of Chemistry 9e

Distribution of Elements - Human Malone and Dolter - Basic Concepts of Chemistry 9e

Names and Symbols of the Elements Symbol - usually the first and second letters of the name For two letter symbols, the first letter is capitalized but the second is not e.g. Li, Be, Ca, Ba, He, Ne Two letters are used for most elements. Exceptions: B, C, F, H, I, K, N, O, P, S, U, V, W, Y Malone and Dolter - Basic Concepts of Chemistry 9e

Names and Symbols of the Elements….continued When the names of two or more elements begin with the same two letters, later letters are used in the symbols. Examples Ruthenium (Ru) Rubidium (Rb) Cerium (Ce) Cesium (Cs) Thorium (Th) Thalium (Tl) (Ta is Tantalum) Malone and Dolter - Basic Concepts of Chemistry 9e

Names and Symbols of the Elements….continued. When the name and symbol use different letters, that means the element was known in antiquity, and the Latin (or other ancient language) name is used as the basis of the symbol. The only exception is Tungsten (W), which uses the German name (Wolfram) Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Examples Ag (Argentium; silver) Au (Aurum; gold) Cu (Cuprum; copper) Fe (Ferrum; iron) Hg (Hydragyrum; mercury) K (Kalium; potassium) Na (Natrium; sodium) Pb (Plumbum; lead) Sb (Stibonium; antimony) Sn (Stannum; tin) Malone and Dolter - Basic Concepts of Chemistry 9e

Objective for Section 2-2 List the postulates of the Atomic Theory Malone and Dolter - Basic Concepts of Chemistry 9e

2-2 The Composition of Elements: Atomic Theory of John Dalton Matter is composed of small indivisible particles called atoms Atoms of the same element are identical and have the same properties Chemical compounds are composed of atoms of different elements combined in small whole-number ratios Chemical reactions are merely the rearrangement of atoms into different combinations Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e John Dalton (1766-1844), founder of the modern atomic theory of matter Malone and Dolter - Basic Concepts of Chemistry 9e

Molecules and Compounds Atoms are the smallest fundamental particle of an element that have the properties of that element Molecules - formed by the chemical combination of two or more atoms Molecular compounds - molecules of atoms of two different elements Covalent bonds - the force holding the atoms together in a molecular compound Malone and Dolter - Basic Concepts of Chemistry 9e

Objective for Section 2-3 List the components of an atom, their relative masses, charges, and location in the atom Malone and Dolter - Basic Concepts of Chemistry 9e

2-3 Composition of the Atom Atoms are composed of three subatomic particles proton - particle with a +1 charge; p electron - particle with a -1 charge; e neutron - particle with no charge; n The proton and the neutron have roughly the same mass (~1 amu or 1.67  10-24 g) The mass of the electron is substantially smaller than the masses of the proton or the neutron Malone and Dolter - Basic Concepts of Chemistry 9e

Electrical Nature of Matter Electrostatic forces attraction between opposite charges repulsion between same charges Ions are charged atoms or molecules cations - positively charged anions - negatively charged Compounds consisting of ions are known as ionic compounds, and the forces holding them together are called ionic bonds Malone and Dolter - Basic Concepts of Chemistry 9e

Nuclear Model of the Atom It was shown that the protons in the atom are found in a very small part of the atom called the nucleus The protons and the neutrons of the atom are found in the nucleus (and are therefore termed nucleons) The electrons are found outside of the nucleus Malone and Dolter - Basic Concepts of Chemistry 9e

Nuclear Model of the Atom Malone and Dolter - Basic Concepts of Chemistry 9e

Objectives for Section 2-4 Define the terms atomic number, mass number, and isotope Using the table of elements, determine the number of protons, neutrons, and electrons in any isotope of an element Demonstrate how the atomic mass of an element is determined from isotopes and their percent abundance Malone and Dolter - Basic Concepts of Chemistry 9e

2-4 Atomic Number, Mass Number, and Atomic Mass Atomic number, Z, is the number of protons in the nucleus The mass number, A, is the total number of nucleons An isotope is an atom of a specific element with a specific mass number Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Isotopes Atoms may have the same atomic number but different mass numbers (meaning the same number of protons but different numbers of neutrons) The atomic number determines the identity of the element Atoms of the same element with differing mass numbers are termed isotopes Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Isotopes Most elements occur naturally as a mixture of isotopes The specific isotope is written using isotopic notation This isotope will be referred to by the mass number e.g. copper-63 Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Isotopic Mass Mass of an isotope compared to a standard The accepted standard is 12C, which is defined as having a mass unit of exactly 12 amu An amu is defined as one-twelfth the mass of an atom of 12C The atomic mass of an element listed in the periodic table is the weighted average of the atomic masses of all isotopes present in nature Malone and Dolter - Basic Concepts of Chemistry 9e

Calculating Atomic Masses For boron, 19.9% occurs as 10B and 80.1% occurs as 11B. The isotopic mass of 10B is 10.013 amu and 11B is 11.009 amu 10B: 0.199  10.013 amu = 1.99 amu 11B: 0.801  11.009 amu = 8.82 amu Atomic mass of boron = 10.81 amu Malone and Dolter - Basic Concepts of Chemistry 9e

Calculating Atomic Masses (2) From the following data, determine the atomic mass of lithium. Atomic mass = 6.015 x 0.0742 + 7.016 x 0.9258 = 6.941 Isotope Mass (amu) %Abundance 6Li 6.015 7.42 7Li 7.016 92.58 Malone and Dolter - Basic Concepts of Chemistry 9e

Calculating Atomic Masses (3) Bromine has two natural isotopes, 79Br and 81 Br. From its atomic mass, estimate the abundance of the two isotopes. From the front cover, the atomic mass of bromine is 79.904, hence the abundance is approximately 50% each. Malone and Dolter - Basic Concepts of Chemistry 9e

Setting a Goal - Part B Compounds and Their Composition You will learn to distinguish between ionic and molecular compounds based upon their chemical structure and general properties Malone and Dolter - Basic Concepts of Chemistry 9e

Objectives for Sections 2-5 and 2-6 Describe the difference between a molecular and ionic compound Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e 2-5 Molecular Compounds A molecule is formed by the chemical combination of two or more atoms Molecules are the basic particles of molecular compounds The atoms in a molecule are held together by a force called the covalent bond Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Formulas A compound is represented by using the symbols for the elements of which it is composed Subscripts are used to indicate how many atoms of a particular element exist in the compound If there is only one atom of a particular element, the one is assumed Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Formulas, cont’d Note that changing the subscripts changes the compound consider H2O and H2O2; SO2 and SO3 Two different compounds can, however, share the same molecular formula dimethyl ether and ethyl alcohol (ethanol) both have the formula C2H6O Malone and Dolter - Basic Concepts of Chemistry 9e

Ethyl Alcohol and Dimethyl Ether Ethyl alcohol on the left; dimethyl ether on the right These species are termed structural isomers Formulas that show the order and arrangement of specific atoms are known as structural formulas Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Isomers Isomers are different compounds (with different structural formulas) but sharing the same molecular formula E.g. H-O-CN cyanic acid H-N=C=O isocyanic acid H-CNO fulminic acid Each has the molecular formula HCNO Malone and Dolter - Basic Concepts of Chemistry 9e

Molecular Elements: Allotropes Hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine, exist as diatomic molecules Some elements exist in a variety of forms, called allotropes e.g. Carbon – graphite; diamond; buckminsterfullerene (etc) Phosphorus - red (Pn) and white (P4) Sulfur – S8 and S4 Malone and Dolter - Basic Concepts of Chemistry 9e

Objective for Section 2-6 Write the formulas of simple ionic compounds given the charges on the ions Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e 2-6 Ionic Compounds Recall that some atoms and molecules can exist as charged species Cations are positively charged ions Anions are negatively charged ions Malone and Dolter - Basic Concepts of Chemistry 9e

How Charged Species Arise Neutral atoms and molecules have the same number of protons and electrons Cations have fewer electrons than protons Anions have more electrons than protons Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Ionic Compounds Formula unit - simplest whole-number ratio of ions in an ionic compound For example: Ca2+ + Br- the resulting formula should be electrically neutral two Br- are needed for each Ca2+ the resulting formula is CaBr2 Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Polyatomic Ions These are cations or anions consisting of groups of atoms that are covalently bonded to each other Examples are NO3-, SO42-, ClO4-, MnO4- When more than one appears in a formula unit, the polyatomic ion is put in between parentheses, and a subscript is used to indicate the number of the ions that appear in the formula unit Malone and Dolter - Basic Concepts of Chemistry 9e

Examples of Polyatomic Ions Ba(ClO4)2, CaCO3 Malone and Dolter - Basic Concepts of Chemistry 9e

Further Examples of Polyatomic Ions NO2+ (nitronium ion: important in the nitration of organic compounds) C6H5CH2+ (benzyl cation; a carbocation) VO2+ (vanadyl cation; an important cation of vanadium) Malone and Dolter - Basic Concepts of Chemistry 9e

Formulas of Ionic Compounds with Polyatomic Ions These are determined the same way as for monoatomic ions The total charge must be zero For Fe3+ and NO3- 1 Fe3+ + 3 NO3- = Fe(NO3)3 Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e Further Examples For Fe2+ and PO43- 3 Fe2+ and 2 PO43- = Fe3(PO4)2 For Fe3+ and C2O42- (oxalate) 2 Fe3+ and 3 C2O42- = Fe2(C2O4)3 Pb2+ and N3- (azide) Pb2+ and 2 N3- = Pb(N3)2 Malone and Dolter - Basic Concepts of Chemistry 9e

Malone and Dolter - Basic Concepts of Chemistry 9e