Atoms and Elements

1. Atoms and Elements Chapter 2 Chapter 2

2. The Atomic Theory of Matter Dalton’s Theory of Matter Dalton’s theory describes the basic unit of matter, the atom. Chapter 2

3. The Atomic Theory of Matter Dalton’s Theory of Matter • Each element is composed of extremely small particles call atoms. • All atoms of a given element are identical; atoms of different elements are different. • Atoms of an element are not changed into different types of atoms by a chemical reaction. • Compounds are formed when atoms of more than one element combine. Chapter 2

4. The Atomic Theory of Matter Dalton’s Theory of Matter Law of Constant Composition In a given compound the relative numbers and kinds of atoms are constant. Chapter 2

5. The Atomic Theory of Matter Dalton’s Theory of Matter Law of Multiple Proportions When two elements form different compounds, the mass ratio of the elements in one compound is related to the mass ratio in the other by a small whole number. Example: Carbon Monoxide (CO)  12g C and 16g O Carbon Dioxide (CO2)  12g C and 32g O There is a 1:2 ratio of oxygen between the two compounds. Chapter 2

6. The Discovery of Atomic Structure • Cathode Rays and Electrons • A cathode ray tube (CRT) is a hollow vessel with an electrode at either end. • The tube is evacuated and then partially filled with a gas. • A high voltage is applied across the electrodes and the gas glows. • Since glowing gas originates from the cathode, it is referred to as a “Cathode Ray”. Chapter 2

7. The Discovery of Atomic Structure Cathode Rays and Electrons Chapter 2

8. The Discovery of Atomic Structure • Characteristics of Cathode Rays • The rays are deflected by magnetic fields. • Metal plates exposed to cathode rays acquire a negative charge. • The rays emitted are independent gas in the cathode tube. Chapter 2

9. The Discovery of Atomic Structure Cathode Rays and Electrons Based on this information, it was determined that cathode rays must be some fundamental particle. Cathode rays are Electrons. Chapter 2

10. The Discovery of Atomic Structure Cathode Rays and Electrons In 1897, Thomson determined the charge to mass ratio of an electron to be 1.76  108 C/g. Chapter 2

11. The Discovery of Atomic Structure • Cathode Rays and Electrons • Millikan determined the charge on an electron to be 1.60 x 10-19 couloumbs. • This was done with the oil drop experiment. Chapter 2

12. The Discovery of Atomic Structure Cathode Rays and Electrons Chapter 2

13. The Modern View of Atomic Structure • 3 Major Components of the Atom • Proton positive (+) charge 1.0073 amu • Neutron no charge 1.0087 amu • Electron negative (-) charge 0.000548 amu • The proton and neutron reside in the nucleus Chapter 2

14. The Discovery of Atomic Structure Radioactivity Radioactivity - The spontaneous emission of radiation. There are three types of radiation Chapter 2

15. The Discovery of Atomic Structure • Radioactivity • Alpha particles (a) • Positive charge. • “Bare” helium atom. • Most massive, least penetrating radiation. • Beta particles (b) • Electron ejected from the nucleus. • Gamma Ray(g) • This is a ray, not a particle. • Most penetrating. Chapter 2

16. The Discovery of Atomic Structure The Nuclear Atom Rutherford’s a-particle experiment: Chapter 2

17. The Discovery of Atomic Structure • The Nuclear Atom • The a-particles were shot through a piece of gold foil. • Most of the a-particles went straight through the foil without deflection. • A few of the particles were scattered. • A very few of the particle were deflected back toward the source. Chapter 2

18. The Discovery of Atomic Structure • The Nuclear Atom • Most of the volume of the atom must consist of a low mass, diffuse negative charge (electron cloud). • The center or nucleus of the atom must consist of a dense positive charge. Chapter 2

19. The Modern View of Atomic Structure Chapter 2

20. The Discovery of Atomic Structure Chapter 2

21. The Modern View of Atomic Structure Isotopes, Atomic Numbers, and Mass Numbers Atomic number (Z) = number of protons in the nucleus. Mass number (A) = total number of protons and neutrons in the nucleus. Chapter 2

22. The Modern View of Atomic Structure Isotopes, Atomic Numbers, and Mass Numbers • In this series of elements, the mass number (A) varies but the atomic number (Z) is constant. • This means that we are looking at a series of isotopes. Chapter 2

23. The Modern View of Atomic Structure Isotopes, Atomic Numbers, and Mass Numbers Isotope - Atom of an element with varying number of neutrons. Chapter 2

24. The Modern View of Atomic Structure Atomic Weight The atomic weight is the weighted average of the mass of the various isotopes of an element in a representative sample. Chapter 2

25. The Modern View of Atomic Structure The Mole • The amount of substance that contains as many elementary entities as there are atoms in exactly 12 g of the carbon-12 isotope. • The amount or number of carbon-12 atoms is: 6.02 x 1023. • This value is also call Avogadro’s number. Chapter 2

26. The Modern View of Atomic Structure Molar Mass • This is simply the mass (in grams) of one mole on any substance. • This number is commonly used as a conversion factor in calculations. Chapter 2

27. The Modern View of Atomic Structure Molar Mass How many moles of phosphorus (P) are contained in 15.51g? Chapter 2

28. The Modern View of Atomic Structure Molar Mass How many grams of boron (B) are contained in 1.289 mol? Chapter 2

29. The Periodic Table Chapter 2

30. The Periodic Table • Metals are located on the left hand side of the periodic table (most of the elements are metals). • Non-metals are located in the top right hand side of the periodic table. • Elements with properties similar to both metals and non-metals are called metalloids and are located at the interface between the metals and non-metals. Chapter 2

31. The Periodic Table • The elements in the periodic table are arranged in such a way that substances that are chemically similar are in a column (called groups). • Columns are numbered from 1A to 8A or 1 to 18. Chapter 2

32. The Periodic Table Chapter 2

33. The Periodic Table • Some of the groups in the periodic table are given special names. • Group 1A: Alkali metals (Li….). • Group 2A: Alkaline earth metals (Be…). • Group 6A: Chalcogens (O…..). • Group 7A: Halogens (F….). • Group 8A: Noble gases (He…..). Chapter 2

34. The Periodic Table • Rows of elements are referred to as periods. Chapter 2

35. End of Chapter Problems 10, 14, 18, 24, 28, 30, 40, 42, 58, 68 Chapter 2