Form 4 Chemistry Definition List

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Chemistry Form 4 Definition List

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).