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Section 3(C-G)

Section 3(C-G). The Nature of Matter. C. Molecules and Atoms. Molecule. the smallest particle of a substance that can exist alone and still have the chemical properties of that substance. Example: water. Atom. the smallest part of an element, which possesses the properties of that element.

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Section 3(C-G)

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  1. Section 3(C-G) The Nature of Matter

  2. C. Molecules and Atoms

  3. Molecule the smallest particle of a substance that can exist alone and still have the chemical properties of that substance. Example: water Atom the smallest part of an element, which possesses the properties of that element.

  4. Molecule Example 1: water One water molecule consists of one oxygen atom and two hydrogen atoms.

  5. Molecule Example 2: carbon dioxide One carbon dioxide molecule consists of one carbon atom and two oxygen atoms.

  6. Molecule Example 3: ammonia One ammonia molecule consists of one nitrogen atom and three hydrogen atoms.

  7. Molecule Example 4: argon One argon molecule consists of one argon atom only.

  8. Most metals are composed of atoms as shown. Atoms

  9. D. Elements and Compounds

  10. A model of oxygen molecules: every oxygen molecule is made up of two oxygen atoms. A model of hydrogen molecules: every hydrogen molecule is made up of two hydrogen atoms. 2.1 What are elements? An element is a substance which are made up of only one kind of atoms. Example oxygen and hydrogen

  11. … about elements Altogether, 109 different elements are known.

  12. Note • 109 kinds of atoms are found. • There are 109 elements • Name of element = name of the atom

  13. States of elements Gas He N O F Ne Cl Ae Br Kr Xe Hg Rn liquids Most elements at room temperature are solids

  14. Gas He N O F Ne Cl Ae Kr Xe Rn

  15. Gas He N O F Ne Cl Ae Kr Xe Rn noble gases

  16. Gas He N O F Ne Cl Ae Kr Xe Rn fluorine and chlorine

  17. Gas He N O F Ne Cl Ae Kr Xe oxygen Rn

  18. Gas He N O F Ne Cl Ae Kr Xe nitrogen Rn

  19. Symbols of Elements: Common metals

  20. Symbols of Elements: Common non-metals

  21. Symbols of Elements: Common semi- metals

  22. Compounds

  23. Compounds A model of water molecule A model of carbon dioxide molecule A compound is a substance whose molecules contain more than one kind of atoms. Examples: water and carbon dioxide

  24. Formulae

  25. Formulae A group of atomic symbols which represent a molecule of an element or a compound Example: O2 The molecule contains two oxygen atoms which are chemically combined together. H2O The molecule contains two hydrogen atoms and one oxygen atom… H2SO4 The molecule contains two hydrogen atoms, one sulphur atom and four oxygen atoms…

  26. Formulae One molecule of phosphorus consists of four phosphorus atoms,….. P4 One molecule of helium contains one helium atom only. He Carbon dioxide molecule contains one carbon atom and two oxygen atoms CO2

  27. Atomicity The number of atoms in a molecule is called its atomicity. Substances of monoatomic molecules: He, Ne, Ar, Kr, Xe, Rn Atomicity of them is ONE. Substances of diatomic molecules: Atomicity of them is TWO. O2, H2, HI, HCl, etc. Substances of triatomic molecules: H2O, H2S, CO2, etc. Atomicity of them is THREE. Molecule containing many atoms is called polyatomic molecule. e.g. S8 Atomicity of is EIGHT.

  28. Naming simple compounds

  29. Compounds containing two elements Examples (molecule containing two atoms only): 1. CO2 Carbon dioxide 2. NO Nitrogen monoxide 3. PCl5 Phosphorus pentachloride 4. PCl3 Phosphorus trichloride Name of the first element: no change

  30. Compounds containing two elements Examples (molecule containing two atoms only): 1. CO2 Carbon dioxide 2. NO Nitrogen monoxide 3. PCl5 Phosphorus pentachloride 4. PCl3 Phosphorus trichloride Name of the first element: no change Name of the second element: end with -ide

  31. Formulae More examples HF: hydrogen fluoride SO2: sulphur dioxide OCl2: oxygen dichloride Sometimes, the prefix mono- is omitted HCl : hydrogen chloride (simple hydrogen compounds) N2O: dinitrogen oxide (no. of atoms of the first element is more than one while the second has one atom only)

  32. Try the exercise!!!

  33. Formulae Carbon disulphide CS2 Sulphur hexachloride SCl6 Hydrogen fluoride Nitrogen dioxide NO2 HF Carbon tetrachloride CCl4 Dinitrogen pentoxide N2O5 Sulphur trioxide Nitrogen monoxide SO3 NO Phosphorus tribromide PBr3 Hydrogen sulphide H2S

  34. End of section 3

  35. Aluminium foil … about elements 94 of the elements are obtained from the Earth’s crust, the sea and the atmosphere. Others are artificially made. Aluminium and carbon are common to us. They are elements.

  36. If the atoms in a molecule are separated, the atoms formed will no longer have the properties of that substance.

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