Chapter 4 perodic table


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Chapter 4 perodic table

  1. 1. Faridahhamat/periodic table/saser CHAPTER 4 : PERIODIC TABLE OF ELEMENTS Historical Development Of The Periodic Table Antoine Lavoisier  The first scientist to classify substances  His classification was unsuccessful because light, heat and a few other compounds were also considered as elements. Johann Dobereiner  Divided the elements into group of three elements with similar chemical properties  The atomic mass of the middle element was approximately the average atomic mass of the other two elements in each triad.  This classification led chemist to realise that there was a relationship between the chemical properties and the atomic mass of each element. John Newlands  Arranged the known elements in order of increasing atomic mass.  The Law of Octaves contributed by him was a failure because the Law was obeyed by the first 17 elements only.  He was the first chemist to show the existence of a periodic pattern for the properties of elements. Lothar Meyer  Plotted a graph of the atomic volume against the atomic mass.  Successful in showing that the properties of the elements formed a periodic pattern against their atomic masses. 1
  2. 2. Faridahhamat/periodic table/saser Dmitri Mendeleev  Arranged the elements in order of increasing atomic mass and grouped them according to similar chemical properties  Left gaps in the table to be filled by undiscovered elements. Henry J.G.Moseley  Concluded that proton number should be the basis for the periodic change of chemical properties instead of the atomic mass.  Rearranged the elements in order of increasing proton number in the Periodic Table. Arrangement Of Elements in the Periodic Table  Elements are arranged in an increasing order of proton number.  Elements with similar chemical properties are placed in the same vertical column  Vertical column of elements in the table is called Group ( Group 1 to Group 18 )  Horizontal row of elements in the table is called Period.  The Group and Period of an element can be known by the electron arrangement.  The number of valence electrons : The position of the Group  The number of shells : Determine the position of the period. Example: X 13 Electron arrangement : 2.8.3 Group : Group 13 and Period : 3 Advantages Of Grouping Elements In The Periodic Table  The systematic arrangement of elements help us to study the elements systematically especially in physical and chemical properties. 2
  3. 3. Faridahhamat/periodic table/saser GROUP 18 ELEMENTS ( Noble / Inert gas )  Consists of helium, neon, argon, krypton, xenon and radon  Noble gases are monoatomic which are very un-reactive and chemically inert.  Because the electron arrangement are stable which the outermost occupied shell are full  Helium has two valence electrons : Duplet electron arrangement  Other noble gases has 8 valence electrons : Octet electron arrangement. Physical Properties Of Group 18 Elements  Colourless gases at room temperature & pressure.  Low melting and boiling point  Low density The Changes Of The Physical Properties Going Down The Group  Atomic size increases  The number of occupied shell in the atom increases from helium to radon  The melting & boiling points increases  The atomic size of each element increases down the group causes the force of attraction between the atom of each element becomes stronger.  The density of element increases Uses Of Group 18 Elements Name Uses Helium In airship, weather balloons Neon In advertising light Argon An inert gas for electric bulbs Krypton Gas-filled electronic devices and laser Xenon Electronic flash guns Radon Natural radioactive gas 3
  4. 4. Faridahhamat/periodic table/saser GROUP 1 ELEMENTS ( The Alkali Metal )  Consists of Lithium, Sodium, Pottassium, Rubidium, Caesium and Francium.  With 1 electron in the outermost shell. Physical Properties Of Group 1  The elements in Group 1 are metals but they have some unusual physical properties. 1. Have silvery and shiny surfaces 2. Soft and can be cut by using a cutter 3. Low density and melting point 4. good conductors of heat and electricity. These physical properties will change gradually when going down the group.  The atomic size increases  The number of occupied shell in the atom increases from lithium to francium  The hardness, melting point and boiling point decrease. Chemical Properties Of Group 1 Elements  Have similar properties but different in reactivity.  The reactivity increases when going down the Group.  Chemical properties : 1. React vigorously with water to produce alkaline metal hydroxide solution and hydrogen gas, H2 Ex: 2 Li + 2 H2O  2 LiOH + H2 2. Burn in oxygen gas rapidly to produce white solid metal oxides. Ex : 4 Li + O2  2 Li2O The metal oxide dissolves in water to form alkaline metal hydroxide solution. Ex : Li2O + H2O  2 LiOH 3. Burn in chlorine gas, Cl2 to form solid metal chlorides Ex: 2 Na + Cl2  NaCl2 Also burn in bromine to form metal bromides. 4
  5. 5. Faridahhamat/periodic table/saser  Alkali metals have 1 e in their outermost occupied shell. So, they will react with other elements by donating 1 e from outermost shell to form ion with charge +1 in order to achieve the stable electron arrangement.  Reactivity increases going down the group  Because the increasing of the atomic size. When going down the group the single valence e in the outermost occupied shell becomes further away from the nucleus. The attraction between the nucleus and valence e becomes weaker. So easier for the atom to donate the single valence e to achieve the stable electron arrangement of the atom of noble gas.  All metals G 1 are extremely reactive, so: 1. must be stored in paraffin oil in bottles 2. do not hold the metal with your bare hand, use forceps 3. Only small piece of alkali metal is used when conducting experiments. GROUP 17 ELEMENTS ( HALOGENS)  Elements in group 17 are poisonous. Consists of fluorine, chlorine, bromine, iodine and astatine.  All halogens exist as diatomic molecules.  Have 7 electrons valence at the outermost shell.  In order to achieve the stable electron arrangement, halogens are required to gain 1 electron to form ion with charge -1. Physical Properties  Low melting and boiling point  Molecules are attracted to each other by weak force.  Melting and boiling points increase when going down the group. So the physical state of halogen at room temperature changes from gas to liquid then to solid.  The atomic size increases with an increase of electron shell, giving rise to an increase in density  The colours of elements ( the colour becomes darker ) Elements Colour Fluorine Pale yellow gas chlorine Greenish-yellow gas Bromine Reddish-brown liquid Iodine Purplish-black solid 5
  6. 6. Faridahhamat/periodic table/saser Why melting and boiling points increase when going down the group? Because the molecular size increases when going down group which causes the van der Waals’ forces among the molecules increase. Chemical properties  Similar chemical properties but different in reactivity.  The chemical properties as below: 1. React with water to form 2 acid Ex : Cl2 + H2O  HCl + HOCl Q : Can you write the chemical equation when bromine and iodine react with water 2. In gaseous state, react with hot iron to form a brown solid iron (III) halides Ex : 2 Fe + 3 Br2  2 FeBr3 Q : Can you write the chemical equation when bromine and iodine react with iron? 3. React with sodium hydroxide to form sodium halide, sodium halite and water. Ex : I2 + 2 NaOH  NaI + NaOI + H2O  Reactivity of element decreases when going down group  The size of atom increasing when going down the group. Thus, the outermost occupied shell of each halogen atom becomes further from the molecule. Therefore, the strength to attract one electron into the outermost occupied shell by the nucleus becomes weaker. Safety Precaution  Handle them in a fume chamber  Use safety goggles and gloves when using halogens.  Always use small amounts of substances.  All the elements are poisonous. 6
  7. 7. Faridahhamat/periodic table/saser ELEMENTS IN A PERIOD Elements of period 3: Element Na Mg Al Si P S Cl Ar Proton number 11 12 13 14 15 16 17 18 Electron 2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8 arrangement Atomic radius 0.156 0.136 0.125 0.117 0.110 0.104 0.099 0.095 (nm) Metallic property Metal Semi- Non-metal metal Physical property Solid Electrical Good Average Non-metal conductivity Electronegatively Increase Across period 3 :  The proton number increases  Atom of the elements has 3 shells occupied with electron.  The number of valence electron in each atom increases.  The atomic radius of elements decreases due to the increasing nuclei attraction on the valence electrons.  The electro negativity of elements increases.  The increase in nuclei attraction on valence electrons and the decrease in atomic size.  Electronegativity : Refer to the measurement of the strength of an atom in its molecule to attract electron towards its nucleus.  Elements change from metallic to non-metallic atom across the period.  The oxides of elements in period change from basic to acidic properties across period 3. Na2O MgO Al2O3 SiO2 P4O10 SO2 Cl2O7 Basic Amphoteric Asidic oxides Oxides oxide Uses Of Semi-metal In Industry  Called metalloids  Weak conductor of electricity 7
  8. 8. Faridahhamat/periodic table/saser  Semi-metal such as : silicon, germanium used as semiconductor ( to make diodes and transistor).  Silicon and germanium have 4 valence electrons, they need to share 4 other valence electrons to achieve the octet arrangement. Thus, they form large covalent molecules, which cannot conduct electricity. However, when heated, covalent bonds breaks and its free valence electrons can conduct electricity. TRANSITION ELEMENTS  These are the elements from group 3 to group 12 in periodic table. Special Characteristic 1. Transition elements show different oxidation number in their compound. 2. Form coloured ions/compound 3. Elements and their compounds are useful catalysts. Example: Platinum --- Ostwald process Nickel --- Manufacture of margarine Vanadium (v) oxide --- Contact process 8