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Chapter 2 Atoms, Molecules, and Ions semester 2/2013 2.2 The Structure of Atom

Chapter 2 Atoms, Molecules, and Ions semester 2/2013 2.2 The Structure of Atom 2.3 Atomic Number, Mass Number, and Isotopes 2.4 The Periodic Table 2.5 Molecules and Ions 2.6 Chemical Formulas Ref: Raymond Chang/Chemistry/ Eleventh Edition Prepared by A. Kyi Kyi Tin.

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Chapter 2 Atoms, Molecules, and Ions semester 2/2013 2.2 The Structure of Atom

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  1. Chapter 2 Atoms, Molecules, and Ions semester 2/2013 2.2 The Structure of Atom 2.3 Atomic Number, Mass Number, and Isotopes 2.4 The Periodic Table 2.5 Molecules and Ions 2.6 Chemical Formulas Ref: Raymond Chang/Chemistry/ Eleventh Edition Prepared by A. Kyi Kyi Tin

  2. 2.2 The Structure of Atom Atom..the basic unit of an element that can enter into chemical combination (extremely small and indivisible) Three subatomic particles…electrons, protons, and neutrons. The Electron (Joseph John Thomson (1856-1940) Negatively charged particles Source: (from cathode ray tube experiment, forerunner of the television tube) The cathode ray is attracted by the plate bearing positive charges and repelled by the plate bearing negative charges, it must consist of negatively charged particles.

  3. Cathode Ray Tube

  4. J.J. Thomson, measured mass/charge of e- (1906 Nobel Prize in Physics)

  5. Radiation…emission and transmission of energy through space in the form of waves.. Radioactivity (Antoine Henri Becquerel(1852-1908) spontaneous emission of particles and / or radiation / Any element that spontaneously emits radiation is “Radioactive”.

  6. (Uranium compound) 2.2

  7. Three types of rays produced by decay of radioactive substances such as “Uranium”.. (i) Alpha ( ) rays..positively charged particles ( ) particles.. deflected by positively charged plate (ii) Beta () rays..electrons..deflected by negatively charged plate (iii) Gamma () rays..high-energy rays..no charge and are not affected by an external field.

  8. (1908 Nobel Prize in Chemistry) • particle velocity ~ 1.4 x 107 m/s (~5% speed of light) • atoms positive charge is concentrated in the nucleus • proton (p) has opposite (+) charge of electron (-) • mass of p is 1840 x mass of e- (1.67 x 10-24 g)

  9. The Proton and the Nucleus 1910,Ernest Rutherford’s experiment (Refer text bk. Pg.47,48) Nucleus…a dense central core within the atom Proton…positively charged particles in the nucleus Source: whenever “. Came close to a nucleus in the scattering experiment, it experienced a large repulsive and therefore a large deflection. (i.e nucleus is composed of positively charged particles, which called proton)

  10. The Neutron (James Chadwick, 1932) • electrically neutral particles having a mass slightly greater than that of protons Particle Mass (g) Charge unit 9.10 x 10 -28 Electron -1 1.67 x 10 -24 Proton +1 Neutron 1.67 x 10 - 24 0 Source: When a thin sheet of beryllium is bombarded with -particles, a very high-energy radiation similar to - rays was emitted by the metal i.e Neutron

  11. mass p = mass n = 1840 x mass e- 2.2

  12. 2.3 Atomic Number, Mass Number, and Isotopes Atomic Number (Z)…the number of protons in the nucleus of each atom of an element. Mass Number (A)… the total number of neutrons and protons present in the nucleus of an atom of an element. Isotopes…atoms that have the same atomic number but different mass number. Mass number Atomic number

  13. 2.4 The Periodic Table • A chart in which elements having similar chemical and physical properties are grounded together. • Groups…Vertical Columns • Periods….Horizontal Rows • Metals….Good conductor of Heat & Electricity • Nonmetals…Poor conductor of heat & electricity • Metalloids….Intermediate b/w Metal & Non-metal • Alkali metals(1A)/ Alkaline Earth metals(2A)/ Halogens( 7A)/ Noble gases (or) Rare gases (8A)

  14. Noble Gas Halogen Alkali Earth Metal Period Alkali Metal Group

  15. 2.5 Molecules and Ions Molecule…an aggregate of at least two atoms in definite arrangement held together by chemical forces (Chemical bonds) SAME ELEMENTS (or) TWO (or) MORE ELEMENTS IN A FIXED RATIO Diatomic molecules same elements (H2,O2,Cl2) different elements (HCl, CO) Polyatomic molecules more than two atoms (O3, H2O,NH3) Ions..an atom or a group of atoms that has a net positive or negative charge. Cations / Anions / monoatomic ions / polyatomic ions

  16. 2.6 Chemical Formulas Molecular Formula…shows the exact number of atoms of each element in the smallest unit of a substance. Allotrope..one of two or more distinct forms of an element (carbon..diamond and graphite) Structural Formula…shows how atoms are bonded to one another in a molecule. Empirical Formula..which elements are present and the simplest whole number ratio of their atoms..

  17. Ionic compounds consist of a combination of cations and an anions. (example Na+Cl-)

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