Chemistry??? What is Chemistry.. i tell U :D

What is Chemistry? - Chemistry is the study of the composition, structure, properties and interactions of matter.

 

In retrospect, the definition of chemistry seems to invariably change per decade, as new discoveries and theories add to the functionality of the science. Shown below are some of the standard definitions used by various noted chemists:

Alchemy (330) – the study of the composition of waters, movement, growth, embodying and disembodying, drawing the spirits from bodies and bonding the spirits within bodies (Zosimos).

Chymistry (1661) – the subject of the material principles of mixt bodies (Boyle).

Chymistry (1663) – a scientific art, by which one learns to dissolve bodies, and draw from them the different substances on their composition, and how to unite them again, and exalt them to an higher perfection (Glaser).

Chemistry (1730) – the art of resolving mixt, compound, or aggregate bodies into their principles; and of composing such bodies from those principles (Stahl).

Chemistry (1837) – the science concerned with the laws and effects of molecular forces (Dumas).

Chemistry (1947) – the science of substances: their structure, their properties, and the reactions that change them into other substances (Pauling).

Chemistry (1998) – the study of matter and the changes it undergoes (Chang).

FORM 4

1. Element – a substance consists of one type of atom.
2. Compound – a substance consists two or more elements that are chemically bonded (molecule or ions).
3. Atom – smallest particle of an element.
4. Molecule – a group of two or more atoms.
5. Ion – a positively charged / negatively charged particle.
6. Isotopes – atoms of the same element with same proton number but different nucleon numbers.
7. Relative atomic mass of an element = the average mass of one atom of an element/((1/12) x the mass of one carbon-12 atom)
8. Relative molecular mass of an element = the average mass of one atom of an molecule/((1/12) x the mass of one carbon-12 atom)
9. Molecule formula – compound shows the actual number of atoms of each element that are present in a molecule of the compound
10. Empirical formula – compound shows the simplest whole number ratio of atoms of each element in the compound
11. Mole – amount of substance that contains as many particles as the number of atoms in exactly 12 g of carbon-12 the symbol of mole is mol.
12. One mole – Avogadro constant – 6.02 x 10²³
13. Group (Periodic Table) – vertical columns of element (similar chemical properties).
14. Periods (Periodic Table) – horizontal rows of element.
15. Valence electrons – electrons that occupy the outermost shell.
16. Ionic bond – bond formed through the transfer of electrons between atoms of metal and non-metal to achieve the stable octet electron arrangement.
17. Ionic compound – consist of positive ions and negative ions which are held by strong electrostatic forces of attraction.
18. Covalent bond – bond formed through the sharing of non-metal electrons to achieve the stable duplet or octet electron arrangement.
19. Covalent compound (also simple molecular structure) – consists of neutral molecules which are held by weak intermolecular forces (Van der Waals).
20. Alkali (base) – chemical substance which ionizes in water to produce hydroxide ions, OH^-.
21. Acid – chemical substance which ionizes in water to produce hydrogen ions, H⁺ or hydroxonium ions, H₃O⁺.
22. pH – degree of acidity or alkalinity of a solution. Scale ranges from 0 to 14.
23. pH value – measure of the concentration of hydrogen ions, H⁺.
24. Strong alkali – ionises (dissociates) completely in water to form hydroxide ions, OH^- of high concentration.
25. Weak alkali – ionises (dissociates) partially in water to form hydroxide ions, OH^- of low concentration.
26. Strong acid – ionises (dissociates) completely in water to form hydrogen ions, H⁺ of high concentration.
27. Weak acid – ionises (dissociates) partially in water to form hydrogen ions, H⁺ of low concentration.
28. Polymer – long chain molecules made up by monomer (repeating unit).

 FORM 5

1. Effective collision (Collision theory) – collision that results in a chemical reaction where the particles collide with the correct orientation and are able to achieve the activation energy.

2. Homologous series – organic compounds (families) with similar formulae and properties.

3. Catalyst – a chemical that alter the rate of reaction.

4. Positive catalyst – increases the rate of reaction & lower the activation energy.

5. Negative catalyst – decreases the rate of reaction & higher the activation energy

6. Organic compounds – carbon-containing compound. Carbon atoms form covalent bonds.

7. Inorganic compounds – compounds from non-living things which do not contain the element carbon.

8. Saturated hydrocarbons – hydrocarbons containing only single bonds between all carbon atoms.

9. Unsaturated hydrocarbons – hydrocarbons containing at least one carbon-carbon double or triple bond.

10. Esterification – esters are produced

11. Vulcanisation – process which makes the natural rubber harder and increases its elasticity by adding sulphur.

12. Redox reaction – chemical reactions involving oxidation and reduction occurring simultaneously.

13. Flavouring – improve the taste or smell of food and restore taste loss due to food processing.

14. Stabilisers – help to mix two liquids that usually do not mix together so that they form an emulsion.

15. Thickeners – substances that thicken food and give the food a firm, smooth and uniform texture.

16. Precipitation – the heat change when one mole of a precipitate is formed from their ions in aqueous solution.

17. Displacement – the heat change when one mole of a metal is displaced from its salt solution by a more electropositive metal.

18. Neutralisation – the heat change when one mole of water is formed from the reaction between an acid and an alkali.

19. Combustion – the heat change when one mole of a substance is completely burnt in oxygen under standard conditions.