70482340 Form 4 Chemistry Definition List

Chemistry Form 4 Definition List 1. Element – a substance consisting of one type of atom. 2. Compound – a substance consisting of two or more elements that are chemically bonded. 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. Proton number – number of protons in the nucleus of an atom. 7. Nucleon number – total number of protons and neutrons in the nucleus of an atom. 8. Isotopes – atoms of the same element with the same proton number but different nucleon numbers. 9. Valence electron – electron in the outermost shell of the atom. 10. Relative atomic mass of an element - the average mass of one atom of an element when compared with 1/12 of the mass of a carbon-12 atom. 11. Molecular formula – a formula that shows the actual number of atoms of each element in a compound. 12. Empirical formula – a formula that shows the simplest ratio of atoms of each element in a compound. 13. One mole – quantity of substance which contains the same number of particles as there are in 12g of carbon-12. 14. Ionic bond – bond which is formed by the transfer of electrons between metal atoms and nonmetal atoms to achieve the stable duplet or octet electron arrangement. 15. Covalent bond – bond which is formed through the sharing of electrons between non-metal atoms to achieve the stable duplet or octet electron arrangement. 16. Acid – chemical substance which ionizes in water to produce hydrogen ions, H+ or hydroxonium ions, H3O+. 17. Electrolyte – substance that can conduct electricity either in molten or aqueous state and undergoes chemical changes. 18. Electrolysis – a process whereby compounds in molten or aqueous state (electrolytes) are broken down into their constituent elements by passing electricity through them. 19. Voltaic cell – a device which converts chemical energy to electrical energy. 20. Electrochemical series – an arrangement of elements based on their tendencies to form ions.

21. Acid - chemical substance which ionizes in water to produce hydroxide ions, OH- or hydroxonium ions, H3O+. 22. Base – chemical substance that can neutralize an acid to produce salt and water only. 23. Alkali - chemical substance which ionizes in water to produce hydroxide ions, OH-. 24. pH value – a measure of the concentration of hydrogen ions, H+ and hydroxide ions, OH-. 25. Strong alkali – alkali which ionizes (dissociates) completely in water to form high concentration of hydroxide ions, OH-. 26. Weak alkali – alkali which ionizes (dissociates) partially in water to form low concentration of hydroxide ions, OH-. 27. Strong acid – acid which ionizes (dissociates) completely in water to form high concentration of hydrogen ions, H+. 28. Weak acid – acid which ionizes (dissociates) partially in water to form low concentration of hydrogen ions, H+. 29. Neutralisation - the reaction between an acid and a base or alkali to produce salt and water. 30. Salt – a compound formed when the hydrogen ion in an acid is replaced by a metal ion or ammonium ion, NH4+. 31. Qualitative analysis of salt – a scheme of test carried out to identify the cation and anion present in a salt. 32. Alloy – a mixture of two or more elements in a certain fixed composition in which the major element is a metal. 33. Polymer – large molecules made up of many smaller and identical repeating units (monomers) joined together by covalent bonds. 34. Synthetic polymers – polymers made in the industry from chemical substances. 35. Composite material – structural material formed by combining two or more materials with different physical properties to produce a complex mixture.

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