GY 111 Lab Notes D Haywick 2007 08 1 GY 111 Lecture Note Series Elemental Chemistry Lecture Goals A Basic Atomic structure Chemistry 101 B The Periodic Table Reference Press et al 2004 Chapter 3 Grotzinger et al 2007 Chapter 3 A Basic atomic structure with apologies to my Chemistry colleagues A bit of history is required before we start into the chemistry stuff During the good old days i e 100 s of years ago chemists were essentially magicians They had learned some basic data about the planet around them including basic elements At the time most people thought that their universe consisted of 4 basic elements 1 Fire 2 water 3 earth 4 air Of course some earth was better than others Gold came from the Earth and was highly sought after Some chemists tried to figure out ways to convert earth into gold They were the alchemists They never really figured out how to do this it is possible but you need a nuclear reactor to do it After a while chemists settled down and actually started to try and figure out the materials that made up the universe They asked a simple question what are the basic building blocks of matter Consider the mineral halite NaCl pictured above from http www geoclassics com halite jpg This mineral has a cubic crystal habit It also has 3 excellent cleavages all at 90 degrees to one another meaning that if you hit halite with a hammer it will always break into smaller and smaller cubes of halite GY 111 Lab Notes D Haywick 2007 08 2 But eventually you come down to a single molecule one sodium particle Na attached to one chlorine particle Cl Up until this century chemists felt that these particles atoms or ions were the basic building blocks of all matter Atoms were defined as the smallest division of matter that retains characteristics of a particular thing Ions were atoms that possessed positive or negative charges we ll get into these shortly Those particular things were called atoms At last count there were just over 100 elements although several of them were produced in labs rather than found in nature Each has a specific chemical symbol The elements can combine through various chemical reactions to for compounds For example water is H2O one part hydrogen 2 parts oxygen galena is PbS one part lead Latin is plumbum 1 part sulfur chalcopyrite is CuFeS2 one part copper 1 part iron 2 parts sulfur Many of the man made elements and even some of the naturally occurring ones are unstable They tend to break apart over time through a process called or radioactivity This must mean that there is something smaller than an atom i e atoms and ions are not the smallest particles It has been known for well over 100 years that atoms are composed of other sub atomic particles The important ones are protons electrons and neutrons Each atom contains various numbers of these particles Protons always carry a single positive charge electrons always carry a single negative charge and neutrons are as the name implies neutral or non charged Each atom contains an equal number of protons and electrons ions contain differing numbers For example GY 111 Lab Notes D Haywick 2007 08 3 The protons and neutrons are held within the nucleus of the atom ion Electrons occur within clouds around the nucleus Electrons do not really orbit the nucleus although it does sometimes help to imagine that they do They are assigned to different energy levels or electron shells Each successive level is at a higher energy level than the previous one and each energy level contains a different maximum number of electrons Level n 1 2 3 4 5 Name K L M N O of electrons 2n2 2 8 18 32 50 Now we need to start thinking about how atomic properties affect minerals The more particles that you have in an atom ion the heavier it becomes But not all particles are created equal Particle Proton Neutron Electron Mass 1 6 x 10 24 g 1 8 x 10 24 g 8 0 x 10 28 g The mass of an electron is about 1 2000th the mass of a proton so electrons can largely be ignored when estimating molecular weights Since all of an elements mass rests in its nucleus the mass of an ion is not significantly different from the mass of an uncharged atom but not all atoms are created equal You have already been told that pure elements are composed of atoms that contain equal numbers of protons and electrons The number of neutrons is not as fixed Take Hydrogen for example Most hydrogen atoms contains 1 electron and 1 proton A much smaller number contain 1 proton 1 electron and 1 neutron or 1 proton 1 electron and 2 neutrons None of these hydrogens are charges all of them contain 1 electron and 1 proton but they all have different masses Consider that a neutron and a proton weigh about the same so the addition of a neutron doubles the mass of the hydrogen atom and 2 neutrons triples its mass As you will discover shortly it is the number of protons and electrons that dictate an elements properties All a neutron does is change the mass of an element So hydrogen with 1 neutron GY 111 Lab Notes D Haywick 2007 08 4 or 2 neutrons is more or less the same element just heavier The same element with different numbers of neutrons are called isotopes Hydrogen has 3 isotopes Usually you indicate different isotopes by placing a number atomic mass adjacent to the chemical symbol e g H1 H2 H3 U235 U238 etc but for hydrogen the isotopes are given specific names Deuterium is used to make heavy water D2O and tritium is radioactive e g T2O is deadly In the late 1960 s scientists started dissecting protons neutrons and other sub atomic particles What we found was that these formerly smallest particles are actually composed of even smaller particles called quarks 3 quarks for each proton neutron Imaginative names were applied to many of them flavor charm red green etc B The Periodic Table of the Elements This is to chemists what the geological time scale is to geologists The table see hand out issued in class organizes all of the elements according to similarities in properties Four important pieces of information can be instantly gleamed form the table For example refer to sodium 1 Name of element 2 Chemical Symbol Latin term is natrium 3 atomic number number of protons in nucleus 4 atomic weight The atomic weight isn t really an actual weight but is in fact a ration between the element in question say sodium and carbon It uses the atomic mass of carbon 1 atomic weight 1 12 carbon mass GY 111 Lab Notes D Haywick 2007 08 5 The rows of the periodic table are arranged to display the elements