CHEMISTRY F4

CHAPTER 4 PERIODIC TABLE4.1 Analyzing the Periodic Table of Elements Historical Development Of The Periodic TableAntoine 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.

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 TableThe systematic arrangement of elements help us to study the elements systematically especially in physical and chemical properties.

4.2 ANALYSING GROUP 18 ELEMENTS: Noble Gases (Monoatomic gas)1. These noble gases in group 18 of the Periodic Table make up almost 1% of the air.

1. All noble gases do not:1. Dissolve in water,1. Conduct electricity1. Conduct heat1. Monoatomic gases at room temperature.Element/SymbolElectron configIncreasing boiling point, melting point, density and radius

Helium, He2

Neon, Ne2.8

Argon, Ar2.8.8

Krypton, Kr2.8.18.8

Xenon, Xe2.8.18.18.8

Radon, Ra2.8.18.32.8

1. Except for He, all of the noble gas atoms have 8 electrons in their outer most shells. This arrangement called the octet configuration.

1. Thus, the arrangement of He (with 2 electrons in outer most shells extremely stable electron arrangement) is duplex electron configuration.

1. Boiling point and melting point are low because they have very low intermolecular force of attraction (Van der Waals force).

1. Density is low because the molecules are far apart from each other (big size molecules will have bigger intermolecular forces of attraction).

1. Low reactivity of noble gases due to unusual high large ionization energies and unusual low electron affinity.

1. Uses:1. Helium super conductors, fill airships and weather balloons, divers tank (80% He, 20% O2), cool metals down.1. Neon advertising light (glow red in low pressure tubes), fill television tubes.1. Argon fill light bulbs (does not react with tungsten filament), welding (prevent hot metal from reacting with O2 from the air).1. Krypton laser surgery, photographic flash lamps.1. Xenon lighthouse lamps (blue light), making electron tubes.1. Radon cancer treatment.4.3 ANALYSING GROUP 1 ELEMENTS: Alkali metals1. They are all metals which react with water to form alkaline solution.

1. All alkali metals are,1. Solid1. Silvery and shiny surfaces1. Soft and melt easily1. Conductors of electricity Element/symbolElectron configDecreasing boiling point, melting point, electro-positivity and hardness.

*only density and radius increasing.

Lithium, Li2.1

Sodium, Na2.8.1

Potassium, K2.8.8.1

1. The melting points, boiling points and hardness of the atoms decrease down the group because the size of the atoms increases down the group causes the metallic bonding between atoms become weaker.

1. The radius of the atoms increases down the group because the lower members have more shells of electrons. Thus, mass of atom increases.

1. The density increases down the group due to its increasing mass and will produce stronger intermolecular attraction. The atoms are closer, resulting in their densities being higher.

1. Electropositivity is a measure of the ability of an atom to lose its valence electrons. The valence electrons of the lower members are further away from the nucleus, and can be easily donated. Thus, electropositivity increases down the group.

1. Chemical properties:1. Reactivity depends on their ability to give away the valence electron (increase down the group).1. Alkali metals react with oxygen gas to form metal oxides. Example:Na(s) O2(g) Na2O1. Alkali metals react with water to form alkaline metal hydroxide solution and hydrogen gas. Example:2K(s) 2H2O() 2KOH(aq) H2(g)1. Alkali metals react with halogen (fluorine, chlorine and bromine) to form colourless, crystalline ionic salts called halides. Example:2Li(s) Cl2(g) 2LiCl(s)2Na(s) Br2() 2NaBr(s)2K(s) I2(s) 2KI(s)

1. Safety precautions:1. Lithium, sodium, and potassium are highly reactive to water and air, thus must be kept under non reactive liquid (paraffin oil).1. Reaction of potassium, rubidium, caesium and francium are explosive. Thus, a small piece should be used always during experiment.1. Never handle those alkali metals with your fingers because it can react with moist which will form a corrosive hydroxide.

4.4 ANALYSING GROUP 17 ELEMENTS: Halogens (diatomic molecules)1. Halogens are not conductors of heat and electricity.

2. At room temperature, chlorine is a gas, bromine is a liquid, and iodine is a solid.Element/symbolElectron configIncreasing boiling point, melting point, density and radius

*reactivity decreases.

Fluorine, F2.7

Chlorine, Cl2.8.7

Bromine, Br2.8.8.7

Iodine, I2.8.18.8.7

Astatine, At2.8.18.18.8.7

3. Physical properties of halogen:

4. Chemical properties of halogen:(a) Halogens react with heated aluminium to produce powdery solid halides. Example:3Cl2(g) 2Al(s) 2AlCl3(s)3Br2() 2Al(s) 2AlBr3(s) (b) Halogens react with phosphorus to form phosphorus halides. (c) Halogens react with H2 to form halides. Example:Cl2(g) H2(s) 2HCl(s)Br2() H2 (s) 2HBr(s)(d) Halogens react among themselves. Example:I2(s) Cl2(g) 2HCl(s)

5. Safety precautions:(a) Vapour of fluorine, chlorine, and bromine are poisonous.(b) Iodine affects negatively the respiration of all living things.(c) Astatine is radioactive. (d) All experiments of halogens should be done inside a fume chamber.(e) Safety goggles and gloves should be used.

4.5 ANALYSING TRANSITION ELEMENTS: Group 3 to group 12.1. All elements in this block of the Periodic Table have similar properties.

1. Physical properties:1. Hard, shiny and dense,1. Good conductors of heat and electricity,1. Are malleable and ductile,1. High tensile strength,1. Radius of all transition elements is almost constant,1. Decreasing from left to right boiling point and melting point1. Increasing from left to right proton number and density, electronegativity (increase slowly).

1. Below are some of the transition elements:ElementsSymbolProton number

ScandiumSc21

TitaniumTi22

VanadiumV23

ChromiumCr24

ManganeseMn25

IronFe26

CobaltCo27

NickelNi28

CopperCu29

ZincZn30

1. Special characteristic:1. Majority of the transition elements have more than one oxidation number in their compounds.ElementsCompoundFormulaOxidation number

ChromiumPotassium dichromate (IV)K2Cr2O7+6

Chromium (II) chloride CrCl3+3

ManganeseManganese (II) chlorideMnCl2+2

Manganese (IV) oxideMnO2+4

Potassium manganate (VI)K2MnO4+6

Potassium manganate (VII)KMnO4+7

IronIron(II) chlorideFeCl2+2

Iron(III) chlorideFeCl3+3

NickelNickel(II) sulphateNiSO4+2

Nickel(III) bromideNiBr3+3

CopperCopper(I) chlorideCuCl+1

Copper(II) oxideCuO+2

1. Most transition elements form coloured ions as shown below:IonsFormula of the ionsColour (aqueous)

Chromate(VI)CrO42-Yellowish

Dichromate(VI)Cr2O72-Orange

Iron(II)Fe2+Greenish

Iron(III)Fe3+Brownish

Copper(II)Cu2+Bluish

Cobalt(II)Co2+Pale reddish

Manganate(VII)MnO4-Purple

Chromium(III)Cr3+Greenish

1. Many of the transition elements are able to from complex ions.

1. Many of the transition elements can act as catalyst. Catalysts are used in chemical reaction to speed up the rate of a reaction. A few industrial processes that use these elements or their compounds as catalysts are:1. Haber process (manufacture ammonia) iron.1. Contact process (manufacture sulphuric acid) Vanadium(V) oxide.1. Ostwald process (manufacture nitric acid) Platinum.1. Hydrogenation of vegetable oil (manufacture margarine) - nickel,1. Advantage of transition elements

Since transition elements speed up chemical processes in industries, they saves time in manufacture Less energy is needed for manufacture in industries, hence lower cost

Since less energy is needed, more energy resources can be conserved, e.g. oil to generate electricity in producing iron. 3OMH