1. Elements and Compounds
Chapter 2
Elements and Compounds

2. 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

3. 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

4. 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

5. Malone and Dolter - Basic Concepts of Chemistry 9e

6. 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
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7. Elements Free in Nature
Only a few elements are found in their free state (not combined with other elements)
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8. 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
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9. Distribution of Elements – the Earth
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10. Distribution of Elements - Human
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11. 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
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12. 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)
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13. 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

14. 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)
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15. Objective for Section 2-2
List the postulates of the Atomic Theory
Malone and Dolter - Basic Concepts of Chemistry 9e

16. 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
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17. Malone and Dolter - Basic Concepts of Chemistry 9e
John Dalton ( ),
founder of the modern
atomic theory of matter
Malone and Dolter - Basic Concepts of Chemistry 9e

18. 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

19. 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

20. 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  g)
The mass of the electron is substantially smaller than the masses of the proton or the neutron
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21. 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
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22. 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
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23. Nuclear Model of the Atom
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24. 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
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25. 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
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26. 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
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27. 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
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28. 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
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29. Calculating Atomic Masses
For boron, 19.9% occurs as 10B and 80.1% occurs as 11B. The isotopic mass of 10B is amu and 11B is amu
10B:  amu = 1.99 amu
11B:  amu = 8.82 amu
Atomic mass of boron = amu
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30. Calculating Atomic Masses (2)
From the following data, determine the atomic mass of lithium.
Atomic mass = x x = 6.941
Isotope
Mass (amu)
%Abundance
6Li
6.015
7.42
7Li
7.016
92.58
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31. 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 , hence the abundance is approximately 50% each.
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32. 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

33. Objectives for Sections 2-5 and 2-6
Describe the difference between a molecular and ionic compound
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34. 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
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35. 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
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36. 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
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37. 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
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38. 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
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39. 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

40. 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

41. 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
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42. 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
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43. 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
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44. 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

45. Examples of Polyatomic Ions
Ba(ClO4)2, CaCO3
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46. 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)
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47. 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 Fe NO3- = Fe(NO3)3
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48. 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
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49. Malone and Dolter - Basic Concepts of Chemistry 9e