Int Chem Chap 4

4 PERIODIC TABLE 4.1 Periodic table of elements

Contribution by Antoine Lavoisier (1743 - 1794) • 1. Antoine Lavoisier, a French chemist, was the first person to classify elements into groups. • 2. In the year 1789, the known elements at that time were classified into four groups as shown in Table 4.1. • 3. In his table, elements were classified into metals and non-metals.

Contribution by Antoine Lavoisier (1743 - 1794)

Contribution by Johann W. Dobereiner (1780 - 1849) • 1. In the year 1829, Johann W. Dobereiner, a German chemist, divided the elements into groups. Each group consisted of three elements with similar chemical properties. He named each of these groups as triad.

Contribution by John Newlands(1837-1898) • 1. In the year 1863, John Newlands, a British chemist, arranged all the known elements according to the ascending order of their atomic masses.

Contribution by Lothar Meyer(1830-1895) • 1. In the year 1870, Lothar Meyer, a German chemist, plotted- a graph of the atomic volume against the atomic mass for all the known elements as shown in Figure 4.1. (The atomic volume of an element is the volume of one mole atom of that element).

Contribution by Dmtri Mendeleev (1839-1907) • 1. Dmitri Mendeleev, a Russian chemistry professor, had shown that the properties of elements changed periodically with their atomic masses. • 2. In the year 1869, he arranged the elements in the same way as Newlands but made a few changes as below. • (a) Elements with similar chemical properties were placed in the same column called a group. • (b) Empty spaces were left in the Periodic Table for those undiscovered elements at that time.

Contribution by H.J.G. Moseley (1887 - 1915) • 1. In the year 1914, H.J.G. Moseley, a British physicist, investigated the X-ray spectrum of elements. • 2. He plotted a graph of the square root of the frequency of X-ray from the elements against their proton numbers. A straight line was obtained. • 3. He concluded that the proton numbers should be used as a basis for the periodic changes in the chemical properties of elements. • 4. Therefore, Moseley arranged the elements in increasing order of their proton numbers. He produced a Periodic Table similar to Mendeleev's Periodic Table.

Arrangement of elements in the Periodic Table • 1. Figure 4.2 shows the Periodic Table.

Arrangement of elements in the Periodic Table

Arrangement of elements in the Periodic Table • Elements with the same number of valence electrons will exhibit similar chemical properties.

4.2

Group 18 Elements

• 1. Elements in Group 18 of the Periodic Table are - helium, neon, argon, krypton, xenon and radon. They are known as noble gases. • 2. Our air consists of approximately 1% of noble gases.

Physical Properties • 1. Table 4.9 lists the physical properties of Group 18 elements.

Physical Properties • Solubility • All noble gases are insoluble in water. • Electrical and heat conductivity • All noble gases cannot conduct electricity and are poor conductors of heat.

Unreactive properties of noble gases • 1. Table 4.10 shows the electron arrangements for the atoms of noble gases.

Unreactive properties of noble gases • 2. The outermost shell of helium atom has 2 electrons, called the duplet electron arrangement whereas the outermost shells of the other noble gases have 8 electrons, called the octet electron arrangement. • 3. The duplet electron arrangement for helium and the octet electron arrangement for the other noble gases are very stable. • 4. Hence, atoms of noble gases do not release electrons, accept electrons or share electrons among each other or with other atoms. • 5. Therefore, all noble gases do not react with other elements or compounds.

Uses of Group 18 elements • Helium • (i) Helium gas is very light and non-flammable (unreactive). • (ii) These properties enable helium gas to be used in filling weather balloons and airships. • Neon • Neon gas is used to fill neon lights which are used to light up advertisement boards. It glows with a reddish-orange colour. • Argon • Argon gas is used td fill electrical bulbs. This is because the hot tungsten filament in the bulb does, not react with inert argon gas. Apart from that, argon gas prevents the oxidation of the filament. • Krypton • The inert krypton gas is used to fill high speed photographic flash lamps. • Radon • Radon gas is used to treat cancer because it is radioactive.

4.3

Group 1 Elements

• Group 1 elements are lithium, sodium, potassium, rubidium, caesium and francium. They are known as alkali metals.

Physical properties

Physical properties • • • • •

General physical properties for Group 1 elements are as follows. (a) All alkali metals are grey solids with shiny surfaces at room conditions. (b) All alkali metals are soft solids and can be easily cut. (c) All alkali metals have low densities compared to heavy metals such as iron and copper. (d) All alkali metals can conduct electricity and heat. (e) All alkali metals have low melting and boiling points compared to heavy metals.

Physical properties

Chemical properties

Chemical properties • 1. All the atoms of alkali metals have one valence electron. Hence, alkali metals exhibit similar chemical properties. • 2. Although the alkali metals have similar chemical properties, the reactivity increases when going down Group 1.

Chemical properties When going down Group 1, the size of alkali metals increases. Hence, the single valence electron become further away from the nucleus. Thus, the single valence electron become more weakly pulled by the nucleus. This causes the single valence electron released more easily to form ions Y  Y+ +e-

Chemical properties • 2Li(s) +

Cl2(g)

• Lithium • 2Na(s) +

chlorine Lithium Chloride Br2 (g)  2NaBr(s)

• Sodium

Bromine Sodium Bromide



2LiCl(s)

Experiment: Investigating the chemical properties of Group 1 elements

Experiment: Investigating the chemical properties of Group 1 elements Discussion: • 1. Lithium, sodium and potassium react with water to produce a colourless gas ('hissing' sound) and alkaline solution that turns red litmus paper blue. Hence, lithium, sodium and potassium exhibit similar chemical properties. • 2. The reactivity of alkali metals in their reactions with water increases from lithium  sodium potassium.

Experiment: Investigating the chemical properties of Group 1 elements • B.

Reactions of alkali metals with oxygen .

Experiment: Investigating the chemical properties of Group 1 elements • Observation:

Experiment: Investigating the chemical properties of Group 1 elements • Discussion: • 1. Lithium, sodium and potassium burn in oxygen gas (air) to produce a white solid which is alkaline when dissolved in water. So, lithium, sodium and potassium exhibit similar chemical properties. • 2. The reactivity of the alkali metals in their reactions with oxygen (air) increases from lithium sodium potassium.

Experiment: Investigating the chemical properties of Group 1 elements

4.4

Group 17 Elements

• 1. Elements in Group 17 are fluorine, chlorine, bromine, iodine and astatine. They are known as halogens. • 2. All halogens exist as diatomic covalent molecules. They are written as F2, Cl2, Br2, I2 and At2. • 3. Halogens are reactive non-metals. They exist in various mineral salts in the earth's crust and sea water.

Physical properties

Physical properties • (a) The colour of halogens becomes darker when going down Group 17. Table 4.20 shows the physical states and colours of various halogens.

Physical properties • (b) All halogens do not conduct electricity. • (c) All halogens are weak conductors of heat. • (d) All halogens have high electronegativity which means the strength of its atom in a molecule to pull electrons towards its nucleus is strong. However, the electronegativity of halogens decreases when going down Group 17 due to the increase in the number of shells occupied with electrons. This causes the outermost occupied shell to become further away from the nucleus.

Chemical properties • 1. Table 4.21 shows the electron arrangements of all halogens from Group 17 of the Periodic Table.

Chemical properties • (a) All atoms of halogens have seven valence electrons. • (b) Each. of these halogen atoms will receive one more electron, either through the transfer of electrons or sharing electrons, to achieve a stable octet electron arrangement during reactions.

Chemical properties • (a) All atoms of halogens have seven valence electrons. • (b) Each. of these halogen atoms will receive one more electron, either through the transfer of electrons or sharing electrons, to achieve a stable octet electron arrangement during reactions. • (c) The reactivity of a halogen is measured by the ease of that halogen atom to receive electrons.

Experiment: Investigating the chemical properties of Group 17 elements • A. Reactions of halogens with water • I. Chlorine with water

Experiment: Investigating the chemical properties of Group 17 elements • Method: • B • I

Reaction of halogens with iron Chlorine with iron

Experiment: Investigating the chemical properties of Group 17 elements • Results:

Experiment: Investigating the chemical properties of Group 17 elements • Discussion: • A Reaction of halogens with water • 1. The solubility of halogens in water decreases when going down Group 17. • 2. All halogens react with water to produce acidic solutions.

Experiment: Investigating the chemical properties of Group 17 elements • A Reaction of halogens with water

Experiment: Investigating the chemical properties of Group 17 elements • Discussion:

• B Reactions of halogens with iron

Experiment: Investigating the chemical properties of Group 17 elements • C Reactions of halogens with sodium hydroxide solution

Elements in a Period • 1. Period is the horizontal row of elements in the Periodic Table. • 2. The Periodic Table consists of seven periods from Period 1 to Period 7. • 3. The period_ number of an element is the number of shells occupied with electrons in an, atom of the element. For example, all the atoms of Period 3 elements have three shells occupied with electrons. • 4. When going across a period from left to right, each atom has one proton more than the previous element. Hence, the proton number increase by one from one element to the next.

Elements in a Period

Change in properties across Period 3 • • • • •

2. Atomic radius (atomic size) 3. Electronegativity 4. Physical states 5. Metallic properties (electropositivity) of elements 6. Electrical conductivity

Properties of oxides of elements in Period 3 • (a) Metals form oxides with basic properties only. • (b) Some metals can form oxides with both basic and acidic properties which are known as amphoteric properties. • (c) Non-metals form oxides with acidic properties only.

Uses of semi-metals (metalloids) in industry • 1. Silicon is widely used in the microelectronic industry. It is used in making diodes, transistors and other electronic components. • 2. These electronic components are joined together on a thin piece of silicon wafer to form an integrated circuit called microchip. • 3. Microchips are used in the manufacture of computers, calculators, cellphones, video cameras, video recorders, televisions and others. • 4. Germanium is also used as a semi-metal (metalloid) in the microclectronic industry.

4 PERIODIC TABLE OF ELEMENTS 4.6 Transition Elements

The position in the Periodic Table • 1. Transition elements are located in Group 3 to Group 12 of the Periodic Table

Properties of transition elements • 2. The properties of transition elements do not change much when going across the period. • (a) The atomic atomic sizes for the first series of transition elements are almost the same. • (b) All transition elements are metals. • 3. Although zinc is located in the first series of transition elements, it does not exhibit the characteristics of transition elements. Thus, it is not a transition element.

Special characteristics of transition elements • All transition elements exhibit four special characteristics as follows. • 1. Form coloured ions/compounds • 2. Exhibit different oxidation numbers in compounds • 3. Form complex ions [Cr(NH3)6]3+ • 4. Act as catalysts