General Chemistry I Virginia State University

1. General Chemistry IVirginia State University Chapter 2 Dr. Vilchiz Summer 2008

2. Atomic Weights • The atomic weight of an element is obtained by adding the products of each isotope’s fractional abundance and its isotopic mass. • Example: Calculate the atomic weight of boron, B, from the following data: • ISOTOPE ISOTOPIC MASS (amu) FRACTIONAL ABUNDANCE • B-10 10.013 0.1978 • B-11 11.009 0.8022

3. Isotope Composition

4. Atomic Weights • Calculate the atomic weight of boron, B, from the following data: • ISOTOPE ISOTOPIC MASS (amu) FRACTIONAL ABUNDANCE • B-10 10.013 0.1978 • B-11 11.009 0.8022 • B-10: 10.013 x 0.1978 = 1.9805 • B-11: 11.009 x 0.8022 = 8.8314 • 10.8119 = • 10.812 amu • ( = atomic wt.)

5. Atomic Weights • Dalton chose Hydrogen to have a mass of 1 “Dalton, ”since he believed it to be the lightest element. • He found that carbon weighed 12 times more than hydrogen. He therefore assigned carbon a mass of 12 “Daltons.”

6. Atomic Weights • Dalton’s atomic weight scale was eventually replaced in 1961, by the present carbon–12 mass scale. • One atomic mass unit (amu) is, therefore, a mass unit equal to exactly 1/12 the mass of a carbon–12 atom. • On this modern scale, the atomic weight of an element is the weighted average atomic mass for the naturally occurring element, expressed in atomic mass units.

7. What is a mole? • A mole is a unit of measurement used to specify amounts of chemical substances. • It is not a unit of mass. • It is similar to “a dozen” • A dozen eggs is not the same as a dozen cars but they are still both a dozen.

8. What is a mole? • A mole is defined as the number of atoms of carbon in 12 g of Carbon-12. (examples) • 1mole=6.022x1023 atoms and can be applied to any moiety • 6.022x1023 is also known as Avogadro’s Number (NA) • 1mol of Carbon=12g Carbon = 6.022x1023 C atoms • 1mol of water= 18g H2O =6.022x1023 water molecules

9. One mole each of various substances.Photo courtesy of American Color.

10. What is a mole? • A mole is defined as the number of atoms of carbon in 12 g of Carbon-12. 1mole=6.022x1023 atoms and can be applied to any moiety • 6.022x1023 is also known as Avogadro’s Number (NA) • 1mol of Carbon=12g Carbon = 6.022x1023 C atoms • 1mol of water= 18g H2O =6.022x1023 water molecules

11. Why the mole? • The mole helps determine amounts of substances and allows for conversion between species. • CaCO3(s) + 2HCl(aq)  CaCl2(aq) + H2CO3(aq) • From this we cannot say 1g of CaCO3 will react with 2 grams of HCl; however, we can say 1mol of CaCO3 reacts with 2 moles of HCl. • 1 mole of CaCO3 is not the same as 1 mole of HCl mass wise, but both have 6.022x1023 molecules.

12. Masses • Isotopic Mass is the mass of an elemental isotope (given in amu). • Atomic Weight is the weighted average of all natural occurring isotopes of an element (amu). • Molecular Mass is the sum of the atomic masses of the atoms in a molecule (amu). • Molar Weight is the weight of one mole of chemical moieties (g/mol).

13. Formula Weight • The formula weight of a substance is the sum of the atomic weights of all the atoms in one formula unit of the compound, whether molecular or not. • For example, one formula unit of NaCl contains 1 sodium atom (23.0 amu) and one chlorine atom (35.5 amu), giving a formula weight of 58.5 amu.

14. Molar Mass Examples • Molar Mass of Ca(C2H3O2)2, Calcium Acetate. 2x(40.1)+4(12.0)+6(1.01)+4(16.0)=198.3g/mol • Molar Mass of Ethylene Glycol, C2H4O2. 2x(12.0)+4(1.01)+2(16.0)=60.0g/mol • Molar Mass of Ammonium Oxalate, (NH4)2C2O4. 2x(14.0)+8x(1.01)+2(12.0)+4(16.0)=124.1g/mol

15. Mass and Moles of a Substance • Mole calculations Example: 2.934g of NaCl = ? Moles NaCl 1.321moles of CuSO4 = ? g CuSO4

16. Periodic Table • In 1870 Mendeleev arranged the known elements in what now is known as the periodic table. • He arranged them in depending on both physical and chemical properties • He predicted both the discoveries of elements and their properties. • Example

17. Mendeleev’s Chemical Chart

18. Periodic Table • In 1870 Mendeleev arranged the known elements in what now is known as the periodic table. • He arranged them in depending on both physical and chemical properties • He predicted both the discoveries of elements and their properties. • Example

19. Eka-Silicon

20. Periodic Table • The term periodic implies that there is something that repeats itself. • In the case of the chemical table it is now known that the repeating pattern is the electron configuration of the outer shell (energy level).

21. The Periodic Table • Periods and Groups • A periodconsists of the elements in one horizontal row of the periodic table. • A group consists of the elements in any one column of the periodic table. • The groups are usually numbered. • Old system IA, …,VIIIA and IB,…,VIIIB • New system 1, 2, 3, …,18 • The eight (A) groups are called main group (or representative) elements.

22. The Periodic Table • Periods and Groups • The “B” groups are called transition elements. • The two rows of elements at the bottom of the table are called inner transition elements. • Elements in any one group have similar properties.

23. Regions of the Periodic Table

24. The Periodic Table • Periods and Groups • The elements in group IA, often known as the alkali metals, are soft metals that react easily with water. • The elements in group IIA are known as the alkali earth metals. • The group VIIA elements, known as the halogens, are also reactive elements. • The group VIIIA elements are known as the noble gases since they seldom react.

25. The Periodic Table • Metals, Nonmetals, and Metalloids • A metal is a substance or mixture that has a characteristic luster and is generally a good conductor of heat and electricity. Usually located to the left of the periodic table. • A nonmetal is an element that does not exhibit the characteristics of the metal. Usually at the right of the periodic table. Nonmetals are bad conductors of both heat and electricity. • A metalloid, or semi-metal, is an element having both metallic and nonmetallic properties. They are found at the boundary between metals and nonmetals in the PT.

26. Group 1A: Alkali MetalsLi, Na, K, Rb, Cs Reaction of potassium + H2O Cutting sodium metal

27. Group 2A: Alkaline Earth Metals Be, Mg, Ca, Sr, Ba, Ra Magnesium Magnesium oxide

28. Group 3A: B, Al, Ga, In, Tl Cu Al Al resists corrosion (here in nitric acid). Gallium is one of the few metals that can be liquid at room temp.

29. Gems & Minerals • Sapphire: Al2O3 with Fe3+ or Ti3+ impurity gives blue whereas V3+ gives violet. • Ruby: Al2O3 with Cr3+ impurity

30. Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO2 Diamond

31. Group 5A: N, P, As, Sb, Bi White and red phosphorus Ammonia, NH3

32. Group 6A: O, S, Se, Te, Po Sulfuric acid dripping from snot-tite in cave in Mexico Elemental S has a ring structure.

33. Group 7A: HalogensF, Cl, Br, I, At

34. Group 8A: Noble Gases He, Ne, Ar, Kr, Xe, Rn

35. Transition Elements Lanthanides and actinides Iron in air gives iron(III) oxide

36. Colors of Transition Metal Compounds Nickel Cobalt Copper Zinc Iron

37. Mass Difference of onemole of substance Return to lecture