CHEMICAL BONDING
Sodium Chloride :
explain how this compound can be formed.
§ Electron arrangement of sodium atom is ...................
§ Sodium atom has …………. valence electron.
§ Sodium atom …………… one electron to form sodium ion, Na+ and achieve a stable …………… arrangement.
§ Electron arrangement of chlorine atom is ...................
§ Chlorine atom has …………. valence electron.
§ Chlorine atom …………… one electron to form chloride ion, Cl- and achieve the stable …………electron arrangement.
§ The sodium ion, Na+ and chloride ion, Cl- formed are attracted to one another with strong force to form a solid sodium chloride, NaCl compound. The attractive ………………..force between the ions is called an ionic bond or electrovalent bond.
patterning exercise [carbon compound]
1. Ethene + Hydrogen
2. Propene + Hydrogen
3. But-2-ene + Hydrogen
4. Ethene + Bromine
5. Propene + Bromine
6. But-2-ene + Bromine
7. Ethene + Hydrogen Chloride
8. Propene + Hydrogen Chloride
9. But-2-ene + Hydrogen Chloride
NOTE : TRY TO ANSWER THIS! YOU CAN SEND YOUR ANSWER TO MY EMAIL.
preparation of soluble salts (not Na, K, NH4+ salt)~ [chapter 8 form 4]
soluble salt : Copper(II) sulphate, CuSO4
Name two chemical substances to prepare the salt : - Sulphuric acid
- Copper (II) Carbonate
Chemical equation : H2SO4 + CuCO3 à CuSO4 + CO2 + H2O
Description : 1. 50 cm3 of acid is measured using a measuring cylinder and poured into a beaker. The acid is heated slowly.
2 Using a spatula, metal / metal oxide / metal carbonate powder is added a little at a time while stirring the mixture with a glass rod.
3. The addition of the solid powder is stopped when some solids no longer
dissolve anymore. (the solid is excess and all the acid is completely
neutralised by the solid)
4. The mixture is filtered to remove the excess solid powder.
5. The filtrate is transferred to an evaporating dish.
6. The filtrate is heated until saturated. (The filtrate is evaporated to
about one-third (1/3) of the original volume).
7. The saturated solution is then allowed to cool to room temperature
and the salt crystals are formed.
sample of question [solving problem using chemical equation]
question:
2HNO3(aq) + CaCO3(s) à Ca(NO3)2 (aq) + H2O(l) + CO2(g)
20 g of calcium carbonate is completely reacted with excess of dilute nitric acid to produce calcium nitrate solution, water and carbon dioxide gas.
Based on the chemical equation, find the volume of carbon dioxide gas released at room condition.
[Relative atomic mass: Ca,40; C,12; O,16; H,1; N,14 ; Molar volume: 24 dm3 at room condition]
problem solving :
Number of moles of CaCO3 = 20 ÷ 100
= 0.2 mole
Based on the equation,
1 mole of CaCO3 produced 1 mole of CO2
Therefore,
0.2 mole of CaCO3 produced 0.2 mole of CO2
So,
0.2 mole of CO2 = 0.2 X 24 dm3
= 4.8 dm3
note : unit is very important in numerical answer, no unit.....no mark that will be given!
Chemistry form 5 [Rate of reaction]
sample question :
When a sodium thiosulphate solution is reacted with hydrochloric acid, the rate of the reaction can be measured by timing how long it takes for a sufficient amount of sulphur to form so that a dark cross drawn on a piece of card below the reaction flask can no longer be seen. 1) What is the rate of reaction if the time taken for the cross to disappear in 50 seconds? Answer: Rate = 1/Time = 1/50s = 0.02/s 2) Write the chemical equation for the reaction above.
Answer: Na2S2O3 (aq) + 2HCl (aq) --> 2NaCl (aq) + S (s) + SO2 (g) + H2O (l)
chemistry form 4 [atom]
The word 'atom' comes from a Greek word that means 'something that invisible'. However, atom can be split!
According to modern atomic theory, subatomic particles like protons and neutrons form the nucleus of an atom, while electrons whirl around the nucleus in different orbits with such a tremendous speed that they seem to form layers of shells around it.
Scientist And His Findings
John Dalton (1766 - 1844)
i) All elements are made up small indivisible particles called atoms.
ii) The atoms of an element are alike but differ from those of other elements.
J.J. Thompson (1856 - 1940)
Suggested the the atom is positively charged sphere with electrons embedded in it.
Ernest Rutherfold (1871 - 1937)
Discovered protons, and suggested thet protons are concentrated in the nucleus - the centre of an atom - which is surrounded by a cloud of electrons.
Niels Bohrs (1885 - 1962)
Proposed that electrons are arranged in orbits surrounding the nucleus.
James Chadwick (1891 - 1974)
Discovered neutrons, and proposed that the nucleus contains protons and neutrons, with electrons moving in orbit surrounding it.
chemistry form 4 [Isotopes identified]
Most atoms have several naturally occurring isotopes. An isotope is an atom that contains a different number of neutrons in its nucleus from that of other atoms of the same element.
This means that different isotopes of an element have different masses, since both protons and neutrons contribute about equally to the mass of an atom.Radioisotopes such as phosphorus-32, carbon-14, sodium-24 and iodine-131 emit radiations. Thus, detectors like Geiger-Müller counter are used to trace the presence of radioactive radiations.Radioisotopes are used in agricultural, medicinal, archaeological and industrial fields.
Some examples of the various uses of radioisotopes are shown as below, in sector;
NUCLEAR ENERGY- Isotope Uranium-235 used to produce nuclear energy.
AGRICULTURE
- Isotope Phosphorus-32 or Nitrogen-15 used to traces the rate of nutrient absorptions in plants.
- Gamma Rays used to sterilises pests. Inhibits the sprouting of potatoes, onions and gingers.
INDUSTRY
- Gamma Rays used to checks wear and tear in engines. Gauges or controls the content level in canned food.
- Strontium-90 used to gauges or controls the thickness of paper and metal in industries.
- Cobalt-60 used to detects crack in metal or concrete structures.
Chemistry form 4 [Periodic table and elements]
1. Lothar Meyer (1830-1895)
This German chemist recognised periodic behaviour based on his graphs of the atomic volume of elements against their atomic weight.
2. Dmitri Mendelev (1834-1907)
This Russian chemist made a table of elements and left a gap for elements that had not yet been discovered.
3. Antoine Lavoisier (1743-1794)
This French chemist classified elements into four groups - gases, non-metals, metals and earths.
4. John Newlands (1837-1898)
This English chemist's law of octaves stated that when elements were placed in the increasing order of atomic weight, the properties of elements fell into a pattern at regular intervals.
5. Henry J. G. Moseley (1887-1915)
This British chemist rearranged the elements in order of increasing atomic number.
6. Johann Dobereiner (1780-1849)
This German chemist proposed the law of triads, which stated that elements came in groups of three.
