Chemistry and Society

1. ChemistryandSociety Matter Spring 2011 Dr. Victor Vilchiz

2. By the end of today… • You should know what isotopes are • You should be able to determine the nuclear symbol of Nuclides • You should know the different parts of the periodic table

3. Matter’s Properties Physical • Color, hardness, density, phase • Changes do not produce a different substance • Frozen water and liquid water = water • Chemical • Matter is changed from one substance into a different substance • Methane burns giving carbon dioxide and water • Change involves rearrangement of how atoms are bonded • Chemical reaction takes place • Methane reacts with oxygen

4. Knowing when • Physical change • Reverse conditions restores original properties of matter • Chemical change • New material has new set of physical properties

5. Compounds • Two or more elements combine • Properties are different then original elements • Na – silver colored metal, reacts violently with water, toxic to humans • Cl – green colored gas, toxic to humans • NaCl = table salt

6. Origin of elements It is believed that after the Big Bang most of the matter was present as hydrogen gas. As temperatures cooled small atoms merged to give bigger ones. Also as temperatures dropped and atoms came together their densities increased and liquids and then solids were formed.

7. The Atom The atom is the smallest unique entity Two atoms of the same element have “almost” identical properties Atoms are the smallest representation of elements. Two atoms can form molecules A molecule is the smallest representation of a compound.

8. Subatomic Particles • The atom is composed of 3 different particles: • Protons • Neutrons • Electrons • Protons and Neutrons reside in the nucleus and are therefore referred to as Nucleons.

9. Subatomic Particles • They have 3 important characteristics: • Mass • Size • Charge

10. Subatomic Particles: Mass While we refer to the mass of objects in the gram range (and kg in the SI system), subatomic particles are much smaller and we must use smaller units. The mass of a proton and the mass of a neutron are about the same and are said to have a mass of 1 atomic mass unit (amu). There are 6.023x1023 amu in one gram of matter. That number is known as Avogadro’s Number (NA)

11. Subatomic Particles: Size Since there are Avogadro's number of amu’s in one gram you probably can imagine that the particles have to be rather small. (Keep in mind that just because something weights little it does not mean it is small) The size of a proton/neutron is about 1x10-12m or about 1 picometer (pm). Electrons have an ill defined shape so it is not possible to assign them a size.

12. Subatomic Particles: Charge Both the electron and the proton have a charge. The charge is the same just opposite in sign. By definition a proton is assign a positive sign and the electron a negative one. A neutron has neither positive or negative charge.

13. Electrostatic forces • Neutrons do not play a large role in chemistry • Chemical reactions deal with the interaction of protons and electrons • The interaction between them is a “Coulombic Attraction” or electrostatic force.

14. Fundamental Forces • There are four types of fundamental forces. • Electrostatic Forces • Repulsion and attraction • Gravity • Only attraction to earth • Strong Nuclear Attractions • Binds the nucleus together • Weak Nuclear Attractions • Responsible for changes in the nuclei (isotopes)

15. Atom Identity The identity of an atom rests in the number of protons found in the nucleus and not the number of electrons or neutrons. Hydrogen 1 proton, 0 neutrons, 1 electron 1 proton, 1 neutron, 1 electron 1 proton, 2 neutrons, 1 electron 1 proton, 0 neutrons, 0 electrons

16. Nuclear Symbols As we can see an atom belonging to a given element may have different compositions. So we must figure out how to represent the different possible configurations.

17. Nuclear Symbols In a nuclear symbol the Z represents the atomic number (# of protons which then dictates X) The X represents the element’s symbol (periodic table) The Y represents the charge of the species (difference between p+s and e-s) The A represents the atomic mass (sum of p+s and ns)

18. Isotopes Atoms that belong to the same element but have different compositions are called isotopes. In the case of Hydrogen ~98% of the hydrogen is present as 1H, ~1.5% as 2H, and <0.5% as 3H. All 3 have 1 proton, 1 electron but the number of neutrons varies.

19. ChemistryandSociety The Periodic Table Spring 2011 Dr. Victor Vilchiz

20. 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?

21. 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.

22. 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.

23. 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.

24. 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.

26. 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.

27. 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.

28. Mendeleev’s Chemical Chart

29. Eka-Silicon

30. The Periodic Table • The Periodic table consists of: • Periods • Groups • Blocks • Families

31. 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

32. 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.

33. 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.

34. 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.

35. 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.