General Chemistry: Chapter 2 Slide 5 of 25 Consequences of Dalton’s theory In forming carbon monoxide, 1.33 g of oxygen combines with 1.0 g of carbon. In the formation of carbon dioxide 2.66 g of oxygen combines with 1.0 g of carbon. Law of Definite Proportions: combinations of elements are in ratios of small whole numbers.
Isotopes of an element Isotopes are different types of atoms (nuclides) of the same chemical element, Z, each having a different atomic mass (A: mass number) Same number of protons, but different number of neutrons. About 339 nuclides occur naturally on Earth, of which 256 (~75%) are stable are known currently General Chemistry: Chapter 2 Slide 21 of 25
Az anyag22 The isotopes of the hydrogen 2 H=D 1 3 H=T 1 1 H=H 1 (t 1/2 ) : years
The relative atomic mass Unit: rest mass of carbon-12 is exactly12. It is the mean of the atomic masses over all the isotopes of the element weighted by isotopic abundance as found in a particular environment (standard: the earth crust). This number may be a fraction which is not close to a whole number, due to the averaging process. General Chemistry: Chapter 2 Slide 27 of 25
Isotopic abundance in the earth crust Az anyag Készítette: Dr. Csonka Gábor egyetemi tanár, 28 ZA Atomic mass abundance%t 1/2 H D T y He Li Be B
Isotopic abundance in the earth crust (2) Az anyag Készítette: Dr. Csonka Gábor egyetemi tanár, 29 ZAAtomic mass abundance%t 1/2 C y N O Cl
30 Boron (Z=5) Isotope composition 19.8 % 10 B m = u 80.2 % 11 B m = u (0.198 u) + (0.802 u) = u The last digit is uncertain due to the variable isotope composition of boron in the earth crust (±0.007 u) Definition: An element consists of the mixture of its isotopes in the earth crust The relative atomic mass (atomic weight) of the boron element:
General Chemistry: Chapter 2 Slide 32 of 25 The Periodic Table Read relative atomic masses. Read the ions formed by main group elements. Read the electron configuration. Learn trends in physical and chemical properties. We will discuss these in detail in Chapter 10.