Structure of atom


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chemistry form 4

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Structure of atom

  1. 1. Particulate Nature of MatterMatter- anything that has mass and occupies spaceParticle + particle = matterIron (Fe) from iron atomNaCl from sodium ionsand chloride ionH2O from watermolecules
  2. 2. Atomsan atom is the smallest particle of an elementexample : “O” for oxygen atomMoleculescontains two or more atoms which are bondedtogether ( maybe same element or not )example : H2 and CCl4Ions-ions are charged either positive or negative-are form in liquid or molten state-lose electron (+ ion),gain electron (- ion)example : Na+, Mg2+, Br-
  3. 3. Kinetic Theory of MatterSolids- strong forces of attraction- particle only vibrate (fixed shape and volume)Liquids- force of attraction weak than solid- particle can move around (follow container shape)Gases- no attraction between particles- particle move faster and freely (zigzag)
  4. 4. Diffusion- example : perfume- light and small particle diffuse faster- heavy and large particle diffuse slow
  5. 5. The Atomic StructureDemocritusDemocritus proposed that if a piece of gold cut intosmaller until cannot cut anymore, called atom.John Dalton (1766-1844)J.J.Thomson (1856-1940)Ernest Rutherford (1871-1937)Neils Bohr (1885-1962)James Chadwick (1891-1974)-----
  6. 6. John Dalton(1766-1844)In 1808, he proposed :1. All matter is composed of atoms.2.Atoms cannot be created or destroyed.3. All the atoms of an element are identical.4.The atoms of different elements are different.5.When chemical reactions take place, atoms ofdifferent elements join together to form compounds.
  7. 7. J.J.Thomson (1856-1940)1. It was the first model of the atom.2. 1897- Thomson discovered the electron (negatively-charged).3. Thomson suggested that an atom is a positively-charged sphere with electrons embedded in it like araisin pudding.
  8. 8. Ernest Rutherford (1871-1937)1. 1914- Rutherford discovered the proton2. Rutherford model was based on the alpha particlescattering experiment3. He proposed1) all the positive charge of an atom is concentratedin the nucleus2) an atom consists of a positively-charged nucleuswith a cloud of electrons surrounding the nucleus
  9. 9. Neils Bohr (1885-1962)He was a student of RutherfordHe proposed1) electrons are arranged in orbits (electron shells)around the nucleus of the atom2) electrons in a particular path have a fixed energy.To move from one orbit to another, an electronmust gain or lose the right amountof energy
  10. 10. James Chadwick (1891-1974)He proposed that the nucleus of the atom containsproton and neutron and the nucleus is surrounded bya cloud of electrons
  11. 11. Atomic structure of an atomAtoms are made of three different types of subatomic particlescalled protons, neutrons and electronsProtons and neutrons are found in the nucleus and they areknown as nucleonsNucleus is positively charged because the protons arepositively charged and the neutrons are electrically neutralElectrons rotate around the nucleus in a certain orbit calledshells, just like planets rotate around the sunSUBATOMIC PARTICLES++protonneutronshellelectron{nucleon
  12. 12. THE PROPERTIES OF SUBATOMIC PARTICLESSubatomicparticlesProton Neutron ElectronSymbol p n e¯Relativeelectriccharge+1 0 -1Relativemass1 1 _1__1840An atom is neutral when it has the same numberof protons and electrons
  13. 13. PROTON NUMBERThe number of protons in an atom of an elementProton number = number of protons
  14. 14. NUCLEON NUMBERThe sum of protons and neutrons in an atomelementNucleon number = number of protons + number of neutrons
  15. 15. The number of protons, electrons and neutrons in aparticular atom are given in the Periodic Table by thenucleon number and proton numberA : proton numberZ :nucleon numberX: symbol of an elementThe number of protons, electrons and neutrons can bedetermined from the nucleon number and proton numberAXZ
  16. 16. Example: (a) AluminiumThe symbol of the element above shows that it isaluminiumNucleon number = 27Proton number = 13Number of neutron =Aluminium atom has 13 protons, 13 electrons and 14neutrons27Al1327 – 13= 14
  17. 17. Symbol of elementsMost symbols are taken from the English nameElement SymbolHydrogenCarbonNitrogenBoronHCNB
  18. 18. Some symbol are made up of two lettersSome symbols are based on the Latin or Greek nameZinc ZnAluminium AlCalcium Casilicon SiSilver AgCopper CuIron FeGold Au
  19. 19. Isotopes and their importanceAre atoms of the same element with the same protonno. but different nucleon no. or neutron no.Isotopes of an element have same chemical propertiesbut different physical propertiesExample: H1H2H3, P31P32
  20. 20. Uses of isotopesMedicine-Cobalt-60 is a radioactive isotope of cobalt. It decaysby giving out gamma radiation. In radiotherapy,maglinant cancer cells are killed by directing a beamof gamma rays towards cancer cellsAgriculture-radiation from radioisotopes is used to sterilise pestssuch as insects that destroy crops.-Fosforus 32 use as fertiliser.Industry-Gamma radiation is used to detect whether cannedfood or bottled drink is completely or partially filled