STUDYSMART CHEMISTRY FORM 4 CHAPTER 4 : PERIODIC TABLE OF ELEMENTS
4.1 Analysing the Periodic Table of Elements 4.2 Analysing Group 18 elements 4.3 Analysing Group 1 elements 4.4 Analysing Group 17 elements 4.5 Analysing elements in a period 4.6 Understanding transition elements
4.1 ANALYSING THE PERIODIC TABLE OF ELEMENTS
Elements in the periodic table are ar ranged horizontally in increasing ordered. Two main component of the periodic table are : a) Group b) Period GROUP The vertical column of elements in the per iodic table arranged according to the number of valance electron in the periodic table are called group. 1 Study Smart www.studysmart.page.tl
There are 18 vertical columns called 1,2,3, until 18 Number of valance electron
1
2
3
4
5
6
7
Group
1
2
3
4
5
6
7
8(except helium) 8
Specific name of group GROUP 1 – 1 – Alkali Alkali Metal GROUP 2 – 2 – Alkali Alkali – Earth Metal – Earth GROUP 3 to GROUP 12 – 12 – Transition Transition metals GROUP 17 – 17 – Halogens Halogens GROUP 18 – 18 – Noble Noble Gas PERIOD The horizontal row of elements in the Per iodic Table consist of the same number of shells occupied with electrons in an elements are called period There are seven horizontal row of elements know as period 1,2…..,7 PERIOD 1 – 1 – Has Has 2 elements PERIOD 2 and PERIOD 3 – 3 – Have Have 8 elements PERIOD 4 and PERIOD 5 – 5 – have have 18 elements PERIOD 6 – 6 – has has 32 elements PERIOD 7 – 7 – has has 23 elements ELEMENTS H He Li Be B C N O F Ne Na Mg Al
PROTON NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13
ELECTRON ARRANGEMENT 1 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.8.1 2.8.2 2.8.3
NUM OF VALANCE ELECTRON 1 2 1 1 3 4 5 6 7 8 1 2 3
GROUP 1 18 1 2 13 14 15 16 17 18 1 2 3
NUM OF SHELLS 1 1 2 2 2 2 2 2 2 2 3 3 3
PERIOD 1 1 2 2 2 2 2 2 2 2 3 3 3
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4.2 ANALYSING GROUP 18 ELEMENTS
Noble gases are monoatomic gases. These noble gases in group 18 of the Periodic Table make up almost 1% o f the air. All noble gases do not: (a) Dissolve in water, (b) Conduct electricity (c) Conduct heat (d) Monoatomic gases at room temperature. Element He Ne Ar Kr Xe Ra
Electron Configuration 2 2.8 2.8.8 2.8.18.8 2.8.18.18.8 2.18.32.8
Increase in boiling point, melting point, density, and radius
Except for He, all of the noble gas atoms have 8 electrons in the ir outer most shells. This arrangement called the octet configuration. Thus, the arrangeme nt of He(with 2 electrons in outer most shells -extremely stable electron arrangement) is duplex duplex electron configuration. Boiling point and melting point are low because they have very low intermolecular force of attraction (Van der Waals force). Density is low because the molecules are far apart from each other (big size molecules will have bigger intermolecular forces of attraction). Low reactivity of noble gases due to unusual high large ionization energies and unusual low electron affinity. Uses: (a) Helium - super conductors, fill airships and weather balloons, diver’s tank diver’s tank (80% He, 20% O2), cool metals down. (b) Neon - advertising light (glow red in low pressure tubes), fill television tubes. (c) Argon - fill light bulbs (does not react with tungsten filament), welding (prevent hot metal from reacting with O2 from the air). (d) Krypton - laser surgery, photographic flash lamps. (e) Xenon- lighthouse lamps (blue light), making electron tubes. (f) Radon - cancer treatment.
4.3 ANALYSING GROUP 1 ELEMENTS
Group 1 element are known as alkali metal They are all metals which react with water to form alkaline solution. All alkali metals are, (a) Solid (b) Silvery and shiny surfaces (c) Soft and melt easily (d) Conductors of electricity 3 Study Smart www.studysmart.page.tl
Element
Electron Configuration
Li
2.1
Na
2.8.1
K
2.8.8.1
Decreasing boiling point, melting point, Electro-positivity and hardness. * only radius and density increase
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. The radius of the atoms increases down the group because the lower members have more shells of electrons. Thus, mass of atom increases. 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. 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. Chemical properties: (a) Reactivity depends on their ability to give away the valence electron (increase down the group). (b) Alkali metals react with oxygen gas to form metal oxides. Example: Na(s) + O2(g) Na2O (c) Alkali metals react with water t o form alkaline metal hydroxide solution and hydrogen gas. Example: 2K(s) + 2H2O(l ) 2KOH(aq) 2KOH(aq) + H2(g) d) 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) Safety precautions: (a) Lithium, sodium, and potassium are highly reactive to water and air, thus must be kept under non-reactive liquid (paraffin oil). (b) Reaction of potassium, rubidium, caesium and francium are explosive. Thus, a small piece should be used always during experiment. (c) Never handle those alkali metals with your fingers because it can react with moist which will form a corrosive hydroxide.
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4.4 ANALYSING GROUP 17 ELEMENTS
Halogens are diatomic molecules Halogens are not conductors of heat and electricity. At room temperature, chlorine is a gas, bromine is a liquid, and iodine is a solid. Elements F
Electronic Configuration 2.7
Increase in boiling point,
Cl
2.8.7
Br
2.8.8.7
I
2.18.8.7
melting point, density, and radius * Reactivity
At
2.8.18.18.8.7
decrease
Physical properties of halogens a) All are coloured b) Non-metal c) Do not conduct electricity d) Have pungent smell (liquid) e) Poisonous f) Cannot conduct conduct heat heat Chemical properties of halogen: (a) Halogens react with heated aluminium to produce powdery solid halides. Example: 3Cl2(g) + 2Al(s) 2AlCl3(s) 3Br2(l ) + 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(l ) + H2 (s) 2HBr(s) (d) Halogens react among themselves. Example: I2(s) + Cl2(g) 2HCl(s) 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.
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4.5 ANALYSING ELEMENTS IN A PERIOD
Horizontal rows in the periodic table There are 7 periods known as period 1,2,3,4,5,6,7 The period number of an elements represe nt the number of shells occupied with elect ron in its atom ELEMENTS Li Na K
PROTON NUMBER 3 11 19
ELECTRON ARRANGEMENT 2.1 2.8.1 2.8.8.1
NUMBER OF SHELL 2 3 4
PERIOD 2 3 4
Period 3 elements ELEMENTS PROTON NUMBER ELECTRON ARRANGEMENT NUCLEAR CHARGE RADIUS
Na 11
Mg 12
Al 13
Si 14
P 15
S 16
Cl 17
Ar 18
2.8.1
2.8.2
2.8.3
2.8.4
2.8.5
2.8.6
2.8.7
2.8.8
+11
+12
+13
+14
+15
+16
+17
+18
0.156
0.136
0.125
0.117
0.110
0.104
0.009
0.001
Physical states changes across the period 3 ( From left to right) Atomic Radius decreases because : a) All the atoms of elements have three shells occupied with electron b) The proton number increased by one unit from one element to the next element c) The number of positive charge in the nucleus increase d) Nuclei attraction on the valance electron incr ease e) The atomic radius of the elements decrease Electronegativity increases a) Electronegativity: The strength of an atom in molecules to attract electron toward its nucleus. b) The atomic radius decrease due to the increasing nuclei attraction on the valance electron c) The strength of nucleus to attr act electron also increase. Metallic properties a) Metal, semi-metal (metalloid), and non-metal properties across the period from le ft to right. b) Metallic properties decreases across the period c) Example : Period 3 : Na, Mg, Al metal Good conductor of electricity The conductivity decrease with increase in temperature
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Si [Semi-metal]
P, S, Cl, Ar [Non-metal]
-Weak electrical conductivity
- Cannot conduct electricity
but increase as temperature rises -Uses : semiconductor In brief ELEMENTS METTALIC PROPERTIES (WITH RESPECT TO ELECTRICAL CONDUCTIVITY CHEMICAL PROPERTIES OF OXIDE ( WITH RESPECT TO REACTION WITH ACID AND ALKALI)
Na
Mg
Al
Metal
Basic oxides
Amphoteric Oxide
Si Semimetal
P
S
Cl
Ar
Non-metal
Acidic Oxides
Metal Good conductor of electricity and hear, shiny surface, ductile and high melting and boiling point Semi-Metal Not a very good conductor of electricity but conductivity increases as temperature and the presence of impurities such boron and phosphorus (doping) Non-Metal Cannot conduct electricity Basic Oxides Metals oxides that can react with acid to form salt and water Acidic Oxide Non-metal oxides that can react with alkali to form salts and water Amphoteric oxide oxides that can react with both alkali and acid to form sal t and water
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4.6 UNDERSTANDING TRANSITION ELEMENTS
Properties of transition elements - First transition series are all m etals - Transition elements have high melting points - They have high density 2+ 3+ - They have variable oxidation state, e.g. Iron (Fe) appear as Fe or Fe 4 4 - They form coloured compounds, e.g. CuSO is blue, FeSO is green 4- They form complex ions, e.g. MnO , Manganate (VII) ions - They act as catalysts Uses of transition elements - Most transition elements and their compounds act as cata lysts which speed up chemical reactions - Iron is used in Haber Process for m anufacture of ammonia - Vanadium (V) oxide is used in contact process to m anufacture sulphuric acid - Nickel is used in hydrogenation of alkenes to form saturated fats (e.g. margarine) 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.
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