Chapter 2 structure of atom


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Chapter 2 structure of atom

  1. 1. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/Faridahhamat/SASER 2006 THEME : MATTER AROUND US LEARNING AREA : 2. THE STRUCTURE OF THE ATOM 2.1 Analysing matter 2.2 Synthesising atomic structure 2.3 Understanding isotopes and assessing their importance 2.4 Understanding the electronic structure of an atom 2.5 Appreciate the orderliness and uniqueness of the atomic structure A Matter PARTICULATE NATURE OF MATTER 1.0 Introduction What is matter?  Matter is anything that occupies space and has mass  Matter is made up of very tiny discrete particles.  These particle can be atoms, molecules and ions [ATOM is the smallest particle of an element. MOLECULE is a group of two or more atoms which are chemically bonded together. ION is an atom or a group of atoms carrying an electric charge. An ion is a positively-charged or negatively-charged particle] MATTER ELEMENT COMPOUND METALS NON METALS IONIC COVALENT COMPOUND COMPOUND ATOM ATOM MOLECULE M ION MOLECULE Sodium Helium Hydrogen NaCl H2O Iron Argon Oxygen PbBr2 NO2 Lead Krypton Nitrogen MgO CO2 Copper neon Chlorine CuSO4 CO Tin Bromine Silver iodine NH3 Zinc Lithium
  2. 2. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006  All substances can be classified into three states of matter; namely solid, liquid and gas Solid  Fixed volume  Fixed shape Liquid  Fixed volume  No fixed shape. Takes the shape of the container it is in Gas  No fixed volume  No fixed shape. Takes the shape of the container it is in 2.0 The State of Matter 1. Matter can exist in three physical states: Solid, liquid and gas. 2. Differences between solid, liquid and gas Property Solid Liquid Gas Arrangement  Very  Closely  Very far of particles closely packed apart from packed  Disorderly each other  Orderly arrangeme  Random manner nt motion Forces of Very strong Strong forces of Very weak forces attraction forces of attraction of attraction between attraction between particles between particles particles between particles but weaker than the forces in solid Motion of Vibrate and rotate Particles can Particles can particles about a fixed vibrate, rotate and vibrate, rotate position move throughout and move freely. the liquid. The rate of collision is greater than the rate of collision in liquid. Diagrammatic representatio n of the particles in each of the physical states Energy Low Moderate High content 2
  3. 3. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 Kinetic Particle Theory 1. The kinetic particle theory is a model to explain the properties of matter 2. The main points of this theory are:  All matter is made up of tiny discrete particles  The particles in matter are always in motion  The kinetic energy of a particle changes with temperature  The average kinetic energy of all particles is directly proportional to the absolute temperature 3.0 Changes in state GAS Boiling Sublimation Condensation Melting SOLID LIQUID Freezing Figure 1 : States of matter Using Kinetic Particle Theory to explain Changes in states of matter 1. Solid to Liquid When a solid is heated, the particles in the solid gain kinetic energy and vibrate more vigorously. The particles vibrate faster as the temperature increases until the energy they gained is able to overcome the forces that hold them at their fixed positions. At this point, the solid becomes a liquid. This process is called melting. The temperature at this point is called the melting points 2. Liquid to Gas When a liquid is heated, its particles absorb the heat energy and move at a faster rate. The kinetic energy of the particles increases. The particles move further apart from one another. When the kinetic energy is enough to overcome the forces of attraction among the liquid particles, liquid changes into gaseous state. At this point, the liquid becomes gas. This 3
  4. 4. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 process is called boiling. The temperature at this point is called the boiling points 3. Gas to Liquid When a gas is cooled, the particles in the gas lose energy and move slower. As the temperature continues to drop, the particles continue to lose more energy until they do not have enough energy to move freely. At this point, the gas becomes liquid. This process is called condensation. The temperature at this point is called the boiling points 4. Liquid to Solid When a liquid is cooled, the particles in the liquid lose energy and move slower. As the temperature continues to drop, the particles continue to lose more energy until they do not have enough energy to move freely. At this point, the liquid becomes a solid This process is called freezing. The temperature at this point is called the freezing points Temperature, oC D liquid B Solid + liquid Solid C A Time, minute Figure 2: Heating curve At point AB: Naphthalene exists as solid. When solid naphthalene is heated, heat energy is absorbed. This causes the particles to gain kinetic energy and vibrate faster. This is why the temperature increases from point A to point B 4
  5. 5. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 At point BC: Solid naphthalene begins to melt. During the melting process, the temperature of matter does not rise, even though heating continues. The temperature remains constant because the heat energy absorbed by particles is used to overcome the forces between solid particles. This constant temperature is the melting point and both solid and liquid are present. At point CD: All the solid has melted (liquid state). From point C to D, the particles in liquid absorb heat energy and move faster. The temperature increases from point C to point D Temperature, oC E F G H Time, minute Figure 3: Cooling curve At point EF: Naphthalene is in the liquid state only. When liquid is cooled, the naphthalene molecules lose heat energy. Their movement shows down and they move closer to each other At point FG: The liquid begins to change into a solid form. There is a mixture of solid and liquid state here. The temperature remains constant because the heat loss to the surroundings is exactly balanced by the heat energy liberated as the particles attract one another to form a solid. The temperature remains constant until all the liquid changes to solid. This is the freezing point of naphthalene. The molecules lose heat and form stronger forces of attraction. Molecules rearrange to form the molecular arrangement of a solid. At point GH: Once all the liquid has become solid, the temperature falls once again until it reaches room temperature. Naphthalene is in the solid state here. The particles in the solid vibrate slower as the temperature decreases 5
  6. 6. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 4.0 Diffusion Diffusion occurs when particles of a substance move in between the particles of another substance. a) Gas Diffusion Air (colourless) Gas jar Reddish-brown Cover vapour spreads Cover is throughout both Reddish brown removed gas jars after Bromine vapour some time Figure 1 : Diffusion of Bromine gas  The bromine particles move in between the air particles  The bromine particles have diffused throughout the air particles b) Liquid Diffusion Purple colour Distilled water spread slowly until after several hours, the whole Potassium After some solution turns Manganate(VII) crystal time purple  Potassium manganate(VII) crystals dissolve in water to produce a solution containing potassium ions, K+ and manganate ions, MnO4-  These ions move randomly in water  K+ and MnO4- ions move and fill up the empty spaces found in between water molecules  Diffusion is slower because there are less empty spaces in liquids than in gases c) Solid Diffusion 6
  7. 7. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 Jelly CuSO4 particle The blue color spreads very slowly upwards through the jelly  Copper(II) sulphate crystals are made up of Cu2+ and SO42- ions.  These ions move upwards and occupy the empty spaces in between jelly particles.  Diffusion is much slower in solids because solid particles are arranged compactly with very little space between particles B The Atomic Structure The Historical development of atomic models Scientist Model Characteristics John Dalton  Atom as a small, indivisible (1803) ball similar to a very tiny ball  Atom cannot be created nor destroyed  All atom of a particular element are the same (have the same mass and physical features) Weakness  Smaller particles are called subatoms  Atom can be created and destroyed ( nuclear reaction)  Atom of the same element can have different physical features (isotopes) J.J  He discovered electron Thomson’s  The atom as a sphere of 7
  8. 8. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 (1897) positive charge which contains a few negatively charge particles called electrons Ernest  He discovered proton Rutherford  The positive charge and (1871 – 1937) most of the mass of the atom are concentrated in a small, central region called nucleus  Electron moves outside the nucleus  Most parts of the atom contain empty space Weakness  The atomic mass calculated using this model is lesser then the actual atomic mass of an element Neil Bohr  The electrons move in (1885 – 1662) shells around the nucleus  Each orbit is at a fixed distance from the nucleus James  Proved the existence of Chadwick neutrons, the neutral (1891-1974) particles in the nucleus  Neutrons contribute approximately to half the mass of an atom 8
  9. 9. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 Subatomic particles of an atom  An atom contains three types of subatomic particles: proton, neutron and electron.  Proton and neutron are found in the nucleus  Electrons move around the nucleus in fixed orbits Particles Symbol Relative charge Relative mass Proton p +1 1 Neutron n 0 1 Electron e -1 1/1840 Proton Electron Nucleus Neutron  The nucleus is positively charged because of the presence of protons, which are positively charged  Neutrons are neutral  Atom contains the same number of electron as the proton because atom is a neutral particle Proton Number and Nucleon Number  Proton number of an element is the number of protons in its atom  Nucleon number of an element is the total number of protons and neutrons in its atom Nucleon Number = number of protons + number of neutrons Nucleon Number = Proton Number + number of neutrons Nucleon number A Symbol of X element Proton Number Z 9
  10. 10. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 C Isotopes Meaning: Isotopes are atoms of the same element containing the same number of protons but different numbers of neutrons [Isotopes are atoms of the same element containing the same proton numbers but different nucleons number] Examples: a) Oxygen – 16 has 8p, 8e, 8n Oxygen - 17 has 8p, 8e, 9n These three different atoms Oxygen – 18 has 8p, 8e, 10n contain 8 protons. This determines that all atoms are oxygen atom b) Carbon – 12 has 6p, 6e, 6n Carbon – 14 has 6p, 6e, 8n Properties Isotopes have the same chemical properties (because they have the same number of protons) but slightly different physical properties such as melting point and density Uses of isotopes in daily life  Iodine -131 used to detect Goiter (penyakit beguk)  Carbon – 14 used to determine age of fossil based on the quantity of carbon -14  Cobalt – 60 used in radiotherapy for treatment of cancer (to kill the cancer cell)  Gamma rays of cobalt-60 are used to destroy bacteria in food without changing the quality of food  The metabolism of phosphorus in plants can be studied using phosphate fertilizers that contain phosphorus-32 10
  11. 11. LESSON NOTES/CHAPTER 2/CHEMISTRY PANEL/FH/SASER 2006 D The Electronic Structure of an Atom  Electron Arrangement of an atom is the arrangement of electron in shells (orbits) around that atom’s nucleus (The electrons in an atom are arranged in shells around the nucleus)  The maximum number of electrons which can fill a particular shell is as follows: Shell Maximum number of electron 1st 2 nd 2 8 rd 3 8 or 18 4th 36  For atoms with proton numbers of 1 to 20, two electrons can occupy in the first shell, eight electrons in the second shell and eight electrons in the third shell [ Electrons occupy the shells closest to the nucleus first. They only start occupying a new shell when the previous one has been occupied] Electron First shell Nucleus Second shell Third shell Figure 1: Neon atom  Valence electron The electrons in the outermost occupied shell are known as valence electrons There are 8 electrons in the outermost occupied shell of the neon atom in Figure 1. Therefore, the valence electrons of a neon atom is 8 11