Chemistry and Society Types of Matter & The Periodic Table Dr. Victor Vilchiz VSU Fall 2006
Alchemy • Is in essence the ancestor of modern chemistry • Alchemy was more than a science • It was a philosophy • A way of life • Alchemists strived to reach pureness and perfection. • Alchemists venerated gold as the symbol of perfection
Alchemy • It was believed that to posses gold will make you rich and pure • To drink gold meant to live forever • Alchemy became the movement to find a way to transform (transmute) matter into gold. • While these believes may seem silly and/or far-fetched they were widely accepted.
The search for the elixir of life • It was known that it was possible to take iron and make steel and that if you mixed copper and zinc you will get brass. • Why wouldn’t be possible to make gold? • Needless to say the search for the elixir was futile and eventually alchemy gave way to new scientific questions and approaches.
Alchemy’s Legacy • While it might be true that alchemy failed to produce an answer to its driving force it was not by any means a waste. • Many process we now use were discovered or developed during the alchemists years. • Distillation • Fermentation • Putrefaction • Many elements were also discovered • Bi, Zn, As, Co, and P
Alchemy to Chemistry • Where does Chemistry come from? • We are not 100% sure where the name comes from but there are several possibilities • It could had come from Egypt Khem = turn black • It could had come from GreeceCheo=to cast • It could had come from ChinaChin-I=gold making juice.
Where to now? • So making gold was not possible… now what? • The obvious question will be then… why can’t we make gold? • The quest to understand what was going on began and thus modern chemistry was born.
Ancient to Modern • In the ancient times of alchemy we had only “AFEW” Elements. • Air • Fire • Earth • Water • Currently we know 116 elements of which only 111 are recognized by the IUPAC.
The study of AIR • Gold was replaced by air as the primary study subject. • It is abundant and it behaves differently under different circumstances. • It was pointed out that at times when air came in contact with lime water it will produced a cloudy solution. • This air was baptized as “Fixed Air” • We now know it as CO2 (carbon dioxide).
Types of AIR • There were other times when air led to fiery explosions. • This type of air is referred to as “explosive” air • It is now known as Hydrogen • Air at times produce very noxious odors. • Thus, it was referred to as “noxious air” • This one is now known as Nitrogen • We are missing one type of air that is very important.
Where did the OO go? • Oxygen was discovered while experiments with mercury (I) oxide were performed. • As HgO is heated a separation of the elements takes place resulting in liquid mercury and gaseous oxygen. • As the experiment was concluded a smoldering piece of wood burst into flames, hence Oxygen was known as “flammable air,” as the just heated HgO sample was placed close by.
Laws of Mass • We are all familiar with the Law of Conservation of Mass • “Matter can not be created nor destroyed” • While this notion is very familiar to us it was not until the 1700’s that it was actually stated: • “Any mass gained by a substance in a process comes from the surroundings”
Conservation of Mass • We all know now that no matter what we do it is impossible to make something out of nothing. • We must have the atoms available to build an item. • “Matter cannot be created nor destroyed” reads the Law of Conservation of Mass. • This means that the final product in a reaction MUST weigh the same as the starting material. • Then why is it that sometimes we seem to violate this law?
Rusting of a Nail • Grab a brand new nail and just to be on the safe side clean it up with sand paper. • Measure the mass of the clean nail. • Then place the nail out in the open for 5 days. • Re-measure the mass of the now rusted nail. • Why does it weigh more than before? • Have we violated the LAW?
Sugar is sugar • There is a second law associated with matter. • It makes sense that no matter where you obtain your sugar you will expect to get the same, sugar. • And the “Law of Definite Compositions” states just that. • No matter where the sugar comes from it will contain 6 atoms of carbon 12 of hydrogen and 6 of oxygen (C6H12O6)
Methane vs Propane • There are times when the same two elements may mix in different mass ratios. • In these cases the ratio difference is small and it will be given using a whole number. • It is impossible to have fractions since we cannot break apart atoms. • Natural Gas is CH4 and Propane is C3H8 • This is the “Law of Multiple Proportions”
Atomic Theory • When the three mass laws come together they yield Dalton’s Atomic Theory. • Dalton revolutionized science by treating “the atom” as the component of substances. • The theory is based on 4 simple assumptions, these assumptions are referred to as the Atomic Theory Postulates.
Postulates of Dalton’s Atomic Theory • Postulates of Dalton’s Atomic Theory • Atoms are the smallest unit of matter. An atom is an extremely small particle of matter that retains its identity during chemical reactions. • Atoms of Element A cannot be converted to Atoms of element B • Atoms of the same element are identical. Each atom of an element has the same properties. Mass is one such property. Thus the atoms of a given element have a characteristic mass. • A compoundis a type of matter composed of atoms of two or more elements chemically combined in fixed proportions.
Atomic Theory Revisited • Postulate #1 atoms are the smallest component of matter • Not true, smallest are protons/electrons and neutrons, but the atoms are the smallest body to retain unique identity • Postulate #2 Atoms of cannot be converted to another element. • Not true, nuclear reactions allows us to do just that
Atomic Theory in Present Times • Dalton’s theory has not been able to withstand all the experiments performed since it was introduced. • The problem with the theory is that it is too simple. • Yet it was revolutionary in its own time. • The Theory tells us about simple ratios of elements in compounds but it does not tells us why. • The theory does not explain charged particles
“New” Experiments and the Atomic Theory • Since Dalton introduced Atomic Theory new experiments have been performed: • Alpha radiation which lead to the discovery of the nucleus • Nucleus is 10,000 x smaller than the atom • Nuclear reactions have been performed • Isotopes were discovered
Atomic Theory of Matter • A chemical reaction consists of the rearrangements of the atoms present in the reacting substances to give new chemical combinations present in the substances formed by the reaction. • Atoms are not created, destroyed, or broken into smaller particles by any chemical reaction.
Atomic Theory Revisited • Postulate #3 atoms of the same element are identical • Not true, isotopes of elements have been discovered where the number of neutrons may vary. • Postulate #4 Ratio of elements in a compound is specific. • Still true While the model was too simple it has been a great starting point.
Matter: Physical State and Chemical Constitution • There are two principal ways of classifying matter: • By its physical state as a solid, liquid, or gas. • By its chemical constitution as an element, compound, or mixture.
Solids, Liquids, and Gases • Solid: Atoms or molecules have a fixed shape. They can be reshape, malleability, can be made into wires, ductile. They are relatively incompressible, fixed volume. (solid example) • Liquid: Atoms or molecules have some freedom to move around and liquid has a fixed volume but no fixed shape. Liquids are slightly compressible. (liquid example) • Gas: Molecules or atoms have freedom to move. Conforms to container shape but it is not volume restricted.(gas example)
Molecular representation of a solid. In a solid each molecule is close to its neighbors and restricted to vibrating back and forth around a specific location. Return to Lecture
Molecular representation of a liquid. In a liquid the molecules are close together, but they can move past each other; each molecule can move a short distance before bumping into one of its neighbors. Return to Lecture
Molecular representation of a gas. In a gas the molecules are much farther apart than in liquids or solids, and they move relatively long distances before colliding with other molecules. Return to Lecture
Chemical Formulas • Chemical formulas are just a quick way of bookkeeping. • They are a quick way to tell us what elements and how many atoms of each compose a substance (compound) • Elements: the simplest form of substance, they cannot be broken down into simpler forms (covered before).
IONS • Ions: are compounds or elements where the number of electrons and protons do not equal each other. • Whichever particle is present in higher amounts gives the sign of the charge the ion has. • The magnitude of the difference is equal to the charge carried by the species
Ion example • In the case of OH, the oxygen provides 8 protons and the hydrogen 1. Therefore, a neutral species will contain a total of 9 protons and 9 electrons. • However, OH-, contains 10 electrons and the same 9 protons… • Electrons are present in excess; therefore, the species has a (-) charge. The difference is 1 hence the charge is (-1).
Charges on ions • Note that while the charge of the ion depends on which particle is present in greater quantity, it is impossible to lose or gain protons. • A positive charge ion has more protons than electrons because it has lost e-’s. • A negative charge ion has more electrons than protons because it has gained e-’s.
Types of Ions • There are two types of ions • Monoatomic: in which an elemental atom looses or gains electrons. • Polyatomic: in which a molecule (many atoms) gain or loose electrons. • All polyatomic ions except 1 are negatively charged. (Ammonium ion NH4+) • Which polyatomic ions should I know? • PO43-, SO42-, SO32-, CO32-,NO3-, NO2-, OH-, CN- and NH4+
Mass of compounds • How do we compare/measure compounds? • Does a dozen eggs weigh the same as a dozen cars? • Of course not • But somehow they seem to be the same right? • When it comes to compounds we use a unit we call the MOLE
MOLE • A mole of compound A has the same number of molecules as a mole of compound B. (just like the dozen eggs is the same number as a dozen cars). • In order to figure out how much a mole weighs we use the atomic mass of each atom in the compound. • H2O: 2 Hydrogen x 1.01g +1 Oxygen x 16.0g • A mole of water weighs 18.0 grams.
The Periodic Table • How is the Periodic Table constructed? • There are many ways to answer this question. • But the real answer might be the most obvious. • PERIODICALLY!!! • Ok so… Periodically but what does it mean to be periodical?
What is a period? • A period is something that repeats itself in a given interval. • We will talk more about periods in the next section. • The periodic table can be said to be organized by the number of protons in the nucleus of elements. (Atomic Number) • It can also be said that it is arranged more or less by atomic mass.
What is the real answer? • As a Physical Chemist in the 21st Century I can tell you that it is arranged according to the electron configuration of the elements. • Uhm can you pass that through me one more time? • The periodic table is arranged according to the number of electrons in the outermost shell in an atom of each element. • For the average person that means what? • Ok, Ok… it has to do with the number of electrons.
That’s Yiddish to me!!! • Imagine if I have my original response back in the 1800’s!!! • I would had been handed my Hemlock and told to make a toast to Socrates. • There were no electrons back then • Lets go back and take it from the 1800’s forward. • Periodic = there are patterns • Lets take several elements and react them.
Periodic Chart in the Beginning • Take for example Sodium and react it with any other element you can find. • Uhm… Na and a series of other elements ( F, Cl, Br, I) react in a 1:1 ratio. • Therefore, F, Cl, I and Br must be grouped. • Replace Na with K, Li or Cu and the same is true. • Therefore, Na, Li, Cu and K belong in the same group.
Periodic Chart in Beginning • Wait a second Cu is not grouped with Na anyway you may look at the periodic table. • This is true!!! • A second set of experiments paired the elements with water… • Na, K, Li react violently with water. • Cu can’t care less about the water • It is obvious then that Cu does but does not belong with Na, K, and Li.
Mendelev and the Table • The first periodic chart was introduced by Mendelev in 1872. It contained 40 elements. • In his chart Mendelev left blank areas for what he said will be elements that will eventually will be discovered. • Not only did he expected these elements to be discovered but he also predicted what their properties were going to be.
The Periodic Table • The Periodic table consists of: • Periods • Groups • Blocks • Families
The Periodic Table • Metals • Metallic Characteristics • Shiny • Malleable (hammer into shape) • Ductile (made into wires) • Form (+) ions • Non-metals • Lack Malleability and ductile ability • Form (-) ions
The Periodic Table • Metalloids • Some of both characteristics • Noble Gases • Do not want to react…hence NOBLE • Halides • Greek for salt • They form binary compounds with atoms from group IA and they are often referred as salts.
The Periodic Table • Alkali Metals • Alkali=basic solution • The metals in this group when placed in water produced basic solutions • Alkaline Earth Metals • The oxides of these metals when placed in water produce basic solutions. • The metal oxides are the most abundant minerals of these metals in the “EARTH”’s crust.
The Periodic Table • Transition Metals • There is small changes in reactivity between them but they transition us from the s-block to the p-block in which there is a big difference in reactivity. • Contain most of the industrial metals • Cu, Ag, AU, Fe, Ni, Zn, Pt, Pd. • Inner Transition Metals • Most are man made and hence contain elements involved in nuclear reactions.
Bonding • There are three types of bonds • Ionic: involves the exchange of electrons and usually occurs between a metal and a non-metal • Covalent: involves the sharing of electrons and usually occurs between two non-metals or a non-metal and a metalloid • Metallic: involves the pooling of electron and involves two metals.
Elements, Compounds, and Mixtures • Millions of substances have been characterized by chemists. Of these, a very small number are known as elements, from which all other substances are made. • An element is a substance that cannot be decomposed by any chemical reaction into simpler substances. (examples) • The smallest unit of an element is the atom.
Elements: mercury, arsenic, sulfur, iodine, magnesium, bismuth. Photo courtesy of American Color. Return to lecture.