Chemistry form 4 chapter 4

Periodic Table of Elements

Group Characteristics

Historical Development of the Periodic Table

Period

Electron Arrangement & Arrangement of Elements

Group 1

Transition Elements

Group 17

Group 18

Scientists 1 Atoinne Lavoiser (1743 – 1794)

Discoveries -In 1789, first Chemist try to classify the substance, include the light & heat into metals & non-metals. -Unsuccessful bcoz light, heat & a few other compounds were also considered as elements

2 Johann W Dobereiner (1780 – 1849)

-In1829,he divided the elements into the groups of 3 elements with similar chemical properties -Known as Dobereiner’s Traid -The atomic mass of the middle element was approximately the average atomic mass of the other 2 elements in each traid. -Traid system was confined to some elements only. -Led chemists to realise that there was a relationship between the chemical properties & the atomic mass of each element.

3 John Newlands -From 1864 – 1865, he arranged the elements in order of increasing ( 1837-1898) atomic mass.

-Elements with similar properties recurred at every 8 element.

-known as the Law of Octaves. -Failure bcoz the Law of Octaves was obeyed by the 17 first elements only. -Shows the existence of a periodic pattern for the properties of elements.

4 Lothar Meyer (1830-1895)

-In 1870 , he plotted graph of the atomic volume against the atomic mass. -Realised that elements with similar chemical properties occupied equivalent positions on the curve. -He found that the properties of the elements formed a periodic pattern against their atomic masses.

5 Dmitri Mendeleev (1834-1907)

-In 1869, he arranged the elements in order of increasing atomic mass & grouped them according to similar chemical properties in vertical coloum. -He left gaps (empty spaces) in the table to be filled by undiscovered elements.

-He was able to predict the properties of undiscovered elements.

6 Hendry J.G. -In 1914,he studied the X-ray spectrum of elements. Moseley (1887- -From experiment, he concluded that proton number should be the 1915) basic for the periodic change of chemical properties instead of the atomic mass. -He arranges the elements in order of increasing proton number in the Periodic Table. Thus, he confirmed the works / Mendeleev. -The modern Periodic Table based on the foundation of Henry J.G Moseley.

1) Arranged according to ascending proton number of the element. 2) 1-18 called Group. 1-7 called periods

Group 1) Group arranged according to the number of valence electron in the outermost shells. 2) All elements in a group a) Have the same valence electrons b) Have the same chemical properties c) Physical properties will change as we go down the group. 3) Groups have special names. Group 1 2 17 18 3-12

Name Alkali metals Alkaline earth metals Halogens Inert (noble) gases Transition metals

4) Group 1,2,13 & transition elements are metals. Group 15-18 are non-metals. Group 14 has 2 non-metals ( carbon& silicon)

Period 1) Period arranged according to the number of shells occupied with electron in an atom. 2) Elements in period 1 – 7 Period Period 1 Period 2 & 3 Period 4 & 5 Period 6 Period 7

Number of elements 2 elements 8 elements 18 elements 32 elements 23 lements

Electrons Arrangement 1) Number of filled electron shells increases, as we go down the group. 2) By knowing the proton number of the element, we can determine the group & period it’s placed in. 3) Relationship between number of valence electrons with the group number of an element. No.of valence electrons

1 2 3 4

5

6

7

8 (second 8. First 8 is in transition elements except helium)

Group 1 2 3 14 15 16 17 18 9) Number of electrons = number of protons 10) The number of shells = period 11) Valence electron = group

12) Maximum number of electron which occupy each shell Shell number 1 2 3 4 Exp:

Maximum number of electrons 2 8 8/18 46

Shell

Valence electron 4 so it is placed in group 14

Electron

Electron arrangement =2.4

Carbon

First shell has 2 electrons & second shell has 4 electrons. So it has 2 shells & it is in period 2.

Element Proton number H 1 He 2 Li 3 Be 4 B 5 C 6 N 7 O 8 F 9 Ne 10 Na 11 Mg 12 Al 13

Electron Number of arrangement electron valence 1 1 2 2 (duplet) 2.1 1 2.2 2 2.3 3 2.4 4 2.5 5 2.6 6 2.7 7 2.8 8(octet) 2.8.1 1 2.8.2 2 2.8.3 3

Group Number of Period shell 1 1 1 18 1 1 1 2 2 2 2 2 13 2 2 14 2 2 15 2 2 16 2 2 17 2 2 18 2 2 1 3 3 2 3 3 13 3 3

Group 18 - Helium(He),Neon(Ne),Argon(Ar),Krypton(Kr),Xenon(Xe) & Radon(Rn) - Noble/inert gases that exists in monoatomic gases.

Physical properties 1) Can’t dissolve in water , can’t conduct electricity & heat 2) Low densities 3) Colorless gaseous state at room temperature & pressure 4) Melting & boiling point is low.

5) Changes of physical properties when going down group 18: Properties Atomic size

Changes Explanation increases Bcoz the number of occupied shells increases.

Melting & increase Bcoz boiling point 1)the atomic size increaseswhen going down the group 2)The force of attraction between particles become stronger 3)Thus, more heat is needed to overcome the stronger force Density increase because the mass increases

Chemical Properties 1) Unreactive/inert 2) Atoms don’t need to donate, accept/share electrons bcoz the electron arrangement of the noble gas atoms are stable.

Uses Elements Helium Neon Argon Krypton Randon Xenon

Uses -Fill air ships/weather balloons -Gas in diving tank -Light up advertising boards/lights -Fill in filament bulbs -Used in flash bulbs & lasers -For cancer treatments -Used in flash bulbs & lasers

Group 1 - Lithium (Li) , Sodium (Na) , Potassium (K) , Rubidium (Rb) , Caesium (Cs) & Francium (Fr) - Known as alkali metals.

Physical properties 1) Conduct heat & electricity 2) High melting point & boiling point 3) All alkali metals are grey in colour with shiny surfaces but they are soft, can cut easily

4) Changes in physical properties going down the group: Properties Changes Explanation Atomic size Increases Because the number of occupied shells increases Melting & Decreases Because boiling point 1)The atomic size increases when going down the group. 2)The metal bond between atoms become weaker 3)Thus,less heat is needed to overcome the weaker bond. Density increases Because increase in atomic size so it became heavier.

Chemical Properties 1) Very reactive elements. 2) The reactivity increases when going down the group. The valence electron in the outermost shell become further from the nucleus. The forces of attraction of nucleus on the valence electron become weaker. The valence electron becomes easier to release.

Chemical properties Reacts with water to produce alkaline metal, hydroxide solutions & hydrogen gas Burns in oxygen gas to produce white, solid metal oxides Burns in chlorine gas to form white solid, metal chloride. X= metals in group 1 (Li,Na,K,Rb,Cs,Fr)

Safety Precautions when handling Alkali metals 1) Kept in paraffin oil 2) Use forceps to take the metal 3) Wear safety goggles & gloves

Chemical equations 2 X + 2 H2O 2 XOH + H2O 4 X + O2

2 X2O

2 X + Cl2

2 XCl

Group 17 1) Fluorine (F) , Chlorine (Cl) , Bromine (Br) , Iodine (I) & Astatine (At) 2) Known as halogens 3) Exists in Diatomic molecules, which F2,Cl2,Br2,I2,At2 4) Non-metals

Physical properties 1) Doesn’t conduct heat & electricity bcoz they consist of covalent molecules. 2) Low melting point & boiling point bcoz their molecules r attracted to each other by intermolecular force.

Force of attraction & intermolecular force are the same. Means the forces between 2 molecules

3) Changes of properties when going down the group 17. Properties Changes Atomic size Increases Melting & boiling Increases point

Colour

Darker

Density

Increases

Physical changes

Explanation Because the number of shells increases Because 1)The atomic size increases when going down the group. 2)The force of attraction between particles become stronger. 3)Thus,more heat is needed to overcome the stronger force. Flourine = pale yellow gas Chlorine = Greenish-yellow gas Bromine = Reddish-brown liquid Iodine = purplish-black solid Because increase in atomic size so it became heavier. change from a gas (fluorine & chlorine) to liquid (bromine) to solid (iodine & astatine)

Chemical Properties 1) Same chemical properties bcoz all halogen atoms have 7 valence electrons but their physical properties are different. 2) Reactivity decreases down the group Chemical properties Reacts with water to produce 2 acids Reacts with hot iron to form a brown solid iron halides Reacts with sodium hydroxide solution,NaOH to form sodium halite(I) & water X = halogens (F,Cl,Br,I,At)

Chemical equations X2 + H2O HX + 3 X2 + 2Fe 2FeX3 X2

+ 2NaOH

HOX

NaOX + H2O

Elements across the period 1) Horizontal rows = periods 2) Consists of 7 periods which periods 1,2 & 3 are short periods. Others are long periods 3) The number of protons in the elements increases across the period from left to right. They increase by 1 proton Element Proton number Electron arrangement Metallic properties Physical properties Electrical conductivity Element oxide

Na Mg 11 12 2.8.1 2.8.2

Al 13 2.8.3

Metals Good base

Si 14 2.8.4 Semi metal Solid Average amphoteric

P 15 2.8.5

S 16 2.8.6

Ci 17 2.8.7

Non-metals Poor acid

Ar 18 2.8.8

Across Period 3 -

Atomic size of elements increases Electropositivity(accept) of elements increases Electropositivity(easy to donate) of elements decreases Electronegativity increases Metallic properties decreases Non-metallic properties increases

Element Sodium Magnesium Aluminum Silicon Phosphorus Sulphur Chlorine Acid-base Base Base Amphoteric Acid Acid Acid Acid properties Reaction X Acid X Acid X Acid X Acid Acid Acid Acid with acidic / X Alkali X Alkali Alkali Alkali Alkali Alkali Alkali alkaline solution X = Insoluble = Soluble

Transition elements 1) Transitions elements have a) Shiny surface b) Ductile c) Malleable ( can easily shaped into different shapes) d) Hard e) High melting point & boiling point f) High density g) Conducts electricity & heat 2) a) Transition elements form coloured compounds & ions Element Ion Colour 3+ Chromium (Cr) Green Cr Yellow CrO2-4 Orange Cr2O2-7 Manganese (Mn) Iron (Fe)

Mn2+ MnO-4 Fe2+

Pale pink Purple Pale green

Cobalt ( Co) Nickel (Ni) Copper (Cu)

Fe3+ Co2+ Ni2+ Cu2+

Yellowish brown Pink Green Blue( CuSO4) Green (CuCO3)

b) Precious stones are coloured bcoz of the presence of these coloured ions in them Gemstone Emerald Amethyst Sapphire Ruby Topaz

Transition metal Ni & Fe Fe & Mn CO & Ti Cr Fe

Colour Green Purple Blue Red Yellow

c) They form complex ions which are coloured,such as: Hexacyanoferrate (II) ion , [Fe(CN)6]4Hexacyanoferrate(II) ion , [Fe(CN)6]3Hexaamina chromium(II) ion , [Cr(NH3)6]3+ Tetraamina copper(II) ion , [Cu(NH3)4]2+ Tetrachlorocuprate(II) ion , [CuCl4]2d) All transition elements except scandium & zinc have more than 1 oxidation numbers. Compound Chromium (III) chloride Potassium (VI) dichromate Manganese (II) sulphate Manganese (IV) oxide Potassium (VII) manganate Iron (II) sulphate Iron (III) chloride Copper (I) oxide Copper (II) sulphate

Formula CrCl3 K2Cr2O7 MnSO4 MnO2 KmNo4 FeSO4 FeCl3 Cu2O CuSO4

Oxidation number +3 +6 +2 +4 +7 +2 +3 +1 +2

e) Transition metals are good catalysts. A specific catalyst is used for a specific reaction,as in, Process Haber process Contact process Ostwald process Hydrogenation

Catalyst Iron filings , Fe Vanadium (V) oxide ( V2O5) Platinum , Pt Nickel , Ni

To manufacture Ammonia Sulphuric acid Nitric acid Margarine

Uses of transition elements in industry 1) Mercury used in thermometer bcoz the melting & boiling point & liquid state are high 2) Tungsten used to make filament bulb as it doesn’t melt easily 3) Iron used to make vehicles, electrical appliances & other products 4) Chromium used to coat iron to prevent rusting of iron substances.