Department of Chemistry CHEM1010 General Chemistry ***********************************************

1. Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel: 931-6325 Email: hzhang@tntech.edu

2. CHEM1010/General Chemistry_________________________________________Chapter 2. (L8)-Introduction to Atoms • Today’s Outline ..Atomic mass revisit: Various types of relative atomic mass ..Atomic mass data accumulating for various elements ..Accumulation of data of physical and chemical properties of various elements ..Attempts to set order for various elements ..Mendeleev’s Periodic Table -How Mendeleev set up his Periodic Table -What does Mendeleev’s Periodic Table look like? -Gap in the table or Map for chemistry?

3. Chapter 2. (L8)-Introduction to Atoms • Atomic mass revisit: Various types of relative atomic mass . Chemists were unable to determine the actual masses of atoms back in 1800’s. ..But chemists were able to find out relative masses of various elements that combined with a given mass of another element. For example, hydrogen can be used to determine the relative masses of other elements: HF, HCl, HBr, HI, H2S, H2O, etc.

4. Chapter 2. (L8)-Introduction to Atoms • Atomic mass revisit: Various types of relative atomic mass ..Dalton used hydrogen to obtain the relative masses of many other elements. ..Later, a scale was used with oxygen given a relative mass of 16.000. ..In 1961, this practice was replaced by a relative mass based on a kind of carbon, which has the relative mass of 12. Based on this new way, the relative mass of elements are now expressed in atomic mass units, or simply units (u).

5. Chapter 2. (L8)-Introduction to Atoms • Accumulation of data of atomic mass and physical and chemical properties for various elements ..Since the time of Lavoisier, many new elements were found, and their physical and chemical properties were also learned more and more. Also, their relative atomic masses were determined. ..the 1800’s and early 1900’s centuries were the times when chemistry witnessed the rapid growth of knowledge about chemical elements. ..By 1830, 55 elements were known.

6. Chapter 2. (L8)-Introduction to Atoms • Attempts to set order for various elements ..With rapid accumulation of knowledge about the chemical elements, chemists started searching a logic or systematical way to organize the chemical elements. ..Dalton made his attempt by arranging the elements according to relative atomic mass. Dalton set up a table of relative atomic mass of a number of elements in his book, A New System of Chemical Philosophy in 1808.

7. Chapter 2. (L8)-Introduction to Atoms • Attempts to set order for various elements ..Precursors of the Periodic Table -Dobereiner(German chemist), “Triads”: three similar elements (Li, Na, K; Ca, Sr, Ba) -De Chancourtois (French geologist), Telluric Helix -Newland (English chemist), every eighth element had similar properties -Meyer (German chemist), came up with a much similar periodic table (1870) to Mendeleev’s (1869)

8. Chapter 2. (L8)-Introduction to Atoms • Mendeleev’s Periodic Table ..The most successful attempt was made by Dmitri Mendeleev, a Russian chemist. ..Mendeleev arranged the elements following atomic mass in an increasing order. ..By this arrangement, a number of properties of the elements exhibit periodic regularity, in other words, they change with atomic mass periodically (with peaks and valleys).

9. Chapter 2. (L8)-Introduction to Atoms • The Periodic Law ..The periodic regularity is called the periodic law: If the elements are listed in order of increasing atomic mass, certain sets of properties recur periodically in this listing. ..Some properties showing periodicity: -atomic volume = atomic mass/density -electrical conductivity -thermal conductivity -hardness

10. Chapter 2. (L8)-Introduction to Atoms • Gap in the table or Map for chemistry? ..In Mendeleev’s Periodic Table, he left some blank spaces or gaps. ..The most amazing thing was he did not think this was a defect of the table, but instead, he predicted existence of some unknown elements to be discovered. ..As an example, three predicted elements were later discovered: Scandium Gallium Germanium

11. Chapter 2. (L8)-Introduction to Atoms • Gap in the table or Map for chemistry? Properties of Germanium: Predicted and Observed PropertyPredicted (1871)Observed (1886) Atomic mass 72 72.6 Density (g/cm3) 5.5 5.47 Color Dirty gray Grayish white Density of Oxide EsO2: 4.7 GeO2: 4.703 Boiling point of chloride EsCl4: < 100 °C GeCl4: 86 °C Density of chloride EsCl4: 1.9 GeCl4: 1.887

12. Chapter 2. (L8)-Introduction to Atoms • Gap in the table or Map for chemistry? ..The powerful predictability of Mendeleev’s Periodic Table makes it become a map for elements. ..This is an excellent example of the power of induction in science. Induction: from particular cases a generalization is formulized and it can predict new particular cases that are unknown.

13. Chapter 2. (L8)-Introduction to Atoms Quiz Time The existence of unknown elements was predicted by (a) the gravitation theory; (b) the periodic appearance of the Sun; (c) Mendeleev’s Periodic Law; (d) circulation of the Earth around the Sun.

14. Chapter 2. (L8)-Introduction to Atoms Quiz Time The discovery of new elements predicted by Mendeleev is (a) a rejection of Mendeleev’s Periodic Law; (b) a failure of Mendeleev’s Periodic Law; (c) a tragedy of Mendeleev’s Periodic Law; (d) a validation of Mendeleev’s Periodic Law.