Metals and Non-metals
Definition of a metal: A metal is an element which will produce positively charge ions (cations) by loss of electrons from its atoms, forming basically electrovalent (ionic) compound.
There are 3 classes of metals: Univalent, Divalent, and Trivalent.
Univalent metals are metals (basically metals with valency 1) that discharge only 1 electron upon operating valency.
E.g. Na à Na+ + e-
K à K+ + e-
Divalent metals are metals (basically metals with valency 2) that discharge only 2 electrons upon operating valency.
E.g. Mg à Mg2+ + 2e-
Ca à Ca2+ + 2e-
Trivalent metals are metals (basically metals with valency 3) that discharge only 3 electrons upon operating valency.
E.g. Al à Al3+ + 3e-
Cr à Cr3+ + 3e-
Properties between Metals and Non-metalsMetals /
Non-Metals
Electrons donars – give away electrons, forming cation / Electrons acceptors – accept electron, forming anion.Can replace H+ in acids to form metallic salts / Cannot replace H+ ions in acids
Forms basic oxides (metallic oxides), forms hydroxyl ions when dissolves in water forming alkaline solution. / Forms acidic oxides or neutral oxides, forming acidic solution when dissolves in water.
Form solid electrovalent (ionic) chlorides, typically not hydrolysed by water. / Form liquid, volatile, covalent chlorides, hydrolysed readily by water (not CCl4).
Reducing agents by electron loss / Oxidizing agents by electron gain
Form few hydrides, when formed the hydrides are solid, electrovalent, attacked by water to give hydrogen and the metallic hydroxide (alkaline solution) / Form many hydrides, which are volatile, covalent, non-electrolytes when anhydrous, and do not liberate hydrogen by the action of water.
Conduct electricity and heat well due to ‘sea of electrons’ / Bad conductor of heat and electricity (rigid molecular structure). C and Si conduct electricity quite well, due to the layers of molecules.
Malleable, Ductile (easily made into wires), lustrous, high density, shiny / Brittle, dull surface, lower density than most metals.
The Electro-Motive Series: Trends
Metal / Electro-Potential (volts) / Electropositive trendsK / +2.92
Na / +2.80
Ca / +2.71
Mg / +1.55
Al / +1.28
Zn / +0.76
Fe / +0.44
Sn / +0.14
Pb / +0.12
H / 0.00
Cu / -0.34
Hg / -0.80
Ag / -0.82
Au / -1.36
1. Displacement of metals
The more electropositive metal will displace off the non-reactive metal in an ionic solution. This displacement takes place by electron transfer from a more electropositive metal (which is been oxidized) to a less electropositive metal (which is been reduced). The ion is discharged and the corresponding metal precipitates.
Zn + CuSO4 à ZnSO4 + Cu (example of metal displacement of Zn and CuSO4)
2. Displacement of metals with acids
Normally, when metals are more electropositive than hydrogen, they tend to displace out hydrogen and replace the H+ ion to form salt.
Some metals liked: K, Na, Ca can displace out hydrogen quickly from cold water.
However, some metals liked: Mg, Al, Zn and Fe cannot displace out H+ ion immediately. Therefore, they can only displace out H+ ion under the condition of steam when heated from diluted acid.
Pb displaces hydrogen slowly from hot, concentrated hydrochloric acid.
Cu, Hg and Ag are the less electropositive metals than hydrogen and never displace directly. Therefore, they are only attacked by oxidizing acids (i.e. by nitric acid or hot conc. Sulphuric acid).
3. Products of electrolysis
The metallic ions in the ionic solution will be discharged to the cathode and precipitate according to the order of electromotive series. The lesser electropositive metals will precipitate first. Thus, those metallic ions which are more electropositive than hydrogen, will remain in the solution. Thus, in copper sulphate solution, since Cu is less electropositive than H, it is been discharged to the cathode. (Cu2+ + 2e- à Cu)
However, the electrolysis situation can be modified by the concentration of the ions in the solution and the type of electrodes used.
4. Nature of oxides
The oxides of K, Na, Ca and Mg are strongly basic except MgO which is sparing basic oxide due to its insufficient solubility.
The oxides of Al, Zn and Pb do not form alkalis as they are totally insoluble in water to liberate with OH- ion. However, they are predominantly basic but with some acidic character as well, i.e. they are amphoteric oxides.
The oxides of Fe, Cu, Hg and Ag are insoluble in water and do not form alkalis. All these oxides are reduced to metals by heating in hydrogen liberating away oxygen to form water. The oxides of Hg and Ag are heated alone to obtain the metals.
5. Nature of carbonates
Carbonates of K and Na are soluble in water and stable to heat.
Carbonates of Ca, Mg, Al, Zn, Fe, Pb and Cu are insoluble in water and decomposed by heat to the oxide of the metal and carbon dioxide.
Hg forms no carbonate.
Ag forms an insoluble carbonate, decomposed by heat leaving the metal, because silver oxide is unstable to heat.
6. Nature of Nitrates
Nitrates of K and Na decompose to nitrites and oxygen.
Nitrates of Ca, Mg, Al, Zn, Fe, Pb and Cu decompose to oxides, nitrogen dioxide and oxygen.
Nitrates of Hg and Ag decompose to the metals, nitrogen dioxide and oxygen. *These oxides are unstable to heat. Nitrates of Hg will leave no residue due to its volatile properties which vaporize at 350oC.
Alloys
The purposes of Alloys are:
· Make the metal mixtures become stronger
· Less malleable and ductile
· More resistant to corrosion
· Better electrical conductivity
· Lower m.p.
Uses of Alloys:
Alloy / Composition / Advantages / UsesBrass / 60 – 80% Cu
20 – 40% Zn / Stronger and more malleable than copper, greater workability because of lower melting pt, more attractive appearance. / Making moving parts of clocks and watches, nuts and bolts, rods, tubes, musical instruments, ornaments and general metal work.
Bronze / 90 – 95% Cu;
5 – 10% Sn / Stronger; greater resistance to chemical attack, more attractive appearance. / Making coins and medals, sculptures and for general metal works
Duralumin / 90 – 95% Al
3 – 5 % Cu
3 – 5 % Mg / Very low density but stronger than aluminum / Construction of aircrafts, ships, buses, rail coaches and piston heads
Steel / 98 – 99.5% Fe;
0.15 – 1.5 % C / More malleable and ductile than iron; harder and stronger; can withstand great stress and strain / Construction of bridges, ships, cars and machinery
Stainless Steel / 90 – 95% Fe;
5 – 10% Cr, Ni / Hard; resistant to corrosion; very attractive in appearance / Making cutlery, tools and surgical instruments
Soft Solder / 50% Pb
50% Sn / Low melting pt; high tensile strength / Welding and Plumbing
Type metal / 70 – 75% Pb;
16 – 20 % Sb
8 – 10% Sn / Low melting point; tough, does not wear out easily. / Printing