Chapter 2 form 4


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Chemistry Chapter 2 form 4
The structure of the Atom

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Chapter 2 form 4

  1. 2. Particulate Nature of Matter <ul><li>Matter- anything that has mass and occupies space </li></ul><ul><li>Particle + particle = matter </li></ul>Iron (Fe) from iron atom NaCl from sodium ions and chloride ion H2O from water molecules
  2. 3. <ul><li>Atoms </li></ul><ul><li>an atom is the smallest particle of an element </li></ul><ul><li>example : “O” for oxygen atom </li></ul><ul><li>Molecules </li></ul><ul><li>contains two or more atoms which are bonded together ( maybe same element or not ) </li></ul><ul><li>example : H2 and CCl4 </li></ul><ul><li>Ions </li></ul><ul><li>-ions are charged either positive or negative </li></ul><ul><li>-are form in liquid or molten state </li></ul><ul><li>-lose electron (+ ion),gain electron (- ion) </li></ul><ul><li>example : Na + , Mg 2+ , Br - </li></ul>
  3. 4. Kinetic Theory of Matter <ul><li>Solids </li></ul><ul><li>- strong forces of attraction </li></ul><ul><li>- particle only vibrate (fixed shape and volume) </li></ul><ul><li>Liquids </li></ul><ul><li>- force of attraction weak than solid </li></ul><ul><li>- particle can move around (follow container shape) </li></ul><ul><li>Gases </li></ul><ul><li>- no attraction between particles </li></ul><ul><li>- particle move faster and freely (zigzag) </li></ul>
  4. 6. <ul><li>Diffusion </li></ul><ul><li>- example : perfume </li></ul><ul><li>- light and small particle diffuse faster </li></ul><ul><li>- heavy and large particle diffuse slow </li></ul>
  5. 8. The Atomic Structure <ul><li>Democritus </li></ul><ul><li>Democritus proposed that if a piece of gold cut into smaller until cannot cut anymore, called atom. </li></ul><ul><li>John Dalton (1766-1844) </li></ul><ul><li>J.J.Thomson (1856-1940) </li></ul><ul><li>Ernest Rutherford (1871-1937) </li></ul><ul><li>Neils Bohr (1885-1962) </li></ul><ul><li>James Chadwick (1891-1974) </li></ul>
  6. 9. John Dalton(1766-1844) <ul><li>In 1808, he proposed : </li></ul><ul><li>All matter is composed of atoms. </li></ul><ul><li>Atoms cannot be created or destroyed. </li></ul><ul><li>All the atoms of an element are identical. </li></ul><ul><li>The atoms of different elements are different. </li></ul><ul><li>When chemical reactions take place, atoms of different elements join together to form compounds. </li></ul>
  7. 10. J.J.Thomson (1856-1940) <ul><li>It was the first model of the atom. </li></ul><ul><li>1897- Thomson discovered the electron (negatively- charged). </li></ul><ul><li>Thomson suggested that an atom is a positively- charged sphere with electrons embedded in it like a raisin pudding. </li></ul>
  8. 11. Ernest Rutherford (1871-1937) <ul><li>1914- Rutherford discovered the proton </li></ul><ul><li>Rutherford model was based on the alpha particle scattering experiment </li></ul><ul><li>He proposed </li></ul><ul><li>1) all the positive charge of an atom is concentrated in the nucleus </li></ul><ul><li>2) an atom consists of a positively-charged nucleus with a cloud of electrons surrounding the nucleus </li></ul>
  9. 12. Neils Bohr (1885-1962) <ul><li>He was a student of Rutherford </li></ul><ul><li>He proposed </li></ul><ul><li>1) electrons are arranged in orbits (electron shells) around the nucleus of the atom </li></ul><ul><li>2) electrons in a particular path have a fixed energy. </li></ul><ul><li>To move from one orbit to another, an electron </li></ul><ul><li>must gain or lose the right amount </li></ul><ul><li>of energy </li></ul>
  10. 13. James Chadwick (1891-1974) <ul><li>He proposed that the nucleus of the atom contains proton and neutron and the nucleus is surrounded by a cloud of electrons </li></ul>
  11. 14. Proton number and nucleon number <ul><li>Proton number = the number of protons in an atom </li></ul><ul><li>Also known atomic number </li></ul><ul><li>No two different element have same proton number </li></ul><ul><li>Atom are neutral. Proton number also tells us number of electron. </li></ul><ul><li>Nucleon number also known mass number </li></ul><ul><li>Nucleon no. = proton no. + neutron number </li></ul><ul><li>How nucleon no. and proton no. of an element is written ? </li></ul>
  12. 15. Symbol of elements <ul><li>Most symbols are taken from the English name </li></ul>H C N B Element Symbol Hydrogen Carbon Nitrogen Boron
  13. 16. <ul><li>Some symbol are made up of two letters </li></ul><ul><li>Some symbols are based on the Latin or Greek name </li></ul>Zinc Zn Aluminium Al Calcium Ca silicon Si Silver Ag Copper Cu Iron Fe Gold Au
  14. 17. Isotopes and their importance <ul><li>Are atoms of the same element with the same proton no. but different nucleon no. or neutron no. </li></ul><ul><li>Isotopes of an element have same chemical properties but different physical properties </li></ul><ul><li>Example of isotopes </li></ul><ul><li>Some isotopes are stable while the rest unstable ( radioactive isotopes) </li></ul>
  15. 18. Uses of isotopes <ul><li>Medicine </li></ul><ul><li>Cobalt-60 is a radioactive isotope of cobalt. It decays by giving out gamma radiation. In radiotherapy, maglinant cancer cells are killed by directing a beam of gamma rays towards cancer cells </li></ul><ul><li>Agriculture </li></ul><ul><li>radiation from radioisotopes is used to sterilise pests such as insects that destroy crops. </li></ul><ul><li>Industry </li></ul><ul><li>Gamma radiation is used to detect whether canned food or bottled drink is completely or partially filled </li></ul>
  16. 19. Electronic structure of an Atom <ul><li>The electron in atom are arranged in shell around its nucleus </li></ul><ul><li>Electron start to fill up the shells from the inner shells </li></ul><ul><li>The first shell is the shell that nearest to nucleus and can hold just 2 electrons </li></ul><ul><li>Second shell can hold 8 electrons </li></ul><ul><li>Third shell can hold 8 electrons </li></ul><ul><li>All of this is called the electron arrangement or electronic configuration of the atom </li></ul><ul><li>Draw electronic arrangement if proton number is 4,5 and 6 </li></ul>
  17. 20. Valence electrons <ul><li>Outermost shell of an atom is called the valence shell </li></ul><ul><li>This shell should have electrons before it can be called a valence shell </li></ul><ul><li>The electrons in the valence shell are called the valence electrons </li></ul><ul><li>Elements with the same number of valence electrons have the same chemical properties </li></ul><ul><li>Lets see the example </li></ul><ul><li>susunan elektron.swf </li></ul>