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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. - PowerPoint PPT Presentation
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the smallest particle of a substance that can exist alone and still have the chemical properties of that substance.
Example: water
the smallest part of an element, which possesses the properties of that element.
Example 1: water
One water molecule consists of one oxygen atom and two hydrogen atoms.
One carbon dioxide molecule consists of one carbon atom and two oxygen atoms.
Example 2: carbon dioxide
One ammonia molecule consists of one nitrogen atom and three hydrogen atoms.
Example 3: ammonia
One argon molecule consists of one argon atom only.
Example 4: argon
Most metals are composed of atoms as shown.
2.1 What are elements?
An element is a substance which are made up of only one kind of atoms.
Example oxygen and hydrogen
A model of hydrogen molecules: every hydrogen molecule is made
up of two hydrogen atoms.
A model of oxygen molecules: every oxygen molecule is made up
of two oxygen atoms.
… about elements
Altogether, 109 different elements are known.
•109 kinds of atoms are found.
•There are 109 elements
•Name of element = name of the atom
Most elements at room temperature are solids
Hg
Br
liquids
N O F
Cl
He
Ne
Ae
KrXe
Rn
Gas
N O F
Cl
He
Ne
Ae
KrXe
Rn
Gas
N O F
Cl
He
Ne
Ae
KrXe
Rn
Gas
noble gases
N O F
Cl
He
Ne
Ae
KrXe
Rn
Gas
fluorine and chlorine
N O F
Cl
He
Ne
Ae
KrXe
Rn
Gas
oxygen
N O F
Cl
He
Ne
Ae
KrXe
Rn
Gas
nitrogen
Metal SymbolAluminium AlBarium BaBeryllium BeCalcium CaChromium CrCobalt CoCopper CuGold AuIron FeLead PbLithium Li
Symbols of Elements: Common metals
Metal SymbolMagnesium MgManganese MnMercury HgNickel NiPlatinum PtPotassium KSilver AgSodium NaTin SnZinc Zn
Non-metal SymbolArgon ArBromine BrCarbon CChlorine ClFluorine FHelium HeHydrogen HIodine INeon NeNitrogen NOxygen OPhosphorus PSulphur S
Symbols of Elements: Common non-metals
Semi-metal SymbolBoron BSilicon Si
Symbols of Elements: Common semi- metals
A compound is a substance whose molecules contain more than one kind of atoms.
Examples: water and carbon dioxide
A model of water molecule
A model ofcarbon dioxide molecule
A group of atomic symbols which represent a molecule of an element or a compound
Example:
O2
H2O
H2SO4
The molecule contains two oxygen atoms which are chemically combined together.
The molecule contains two hydrogen atoms and one oxygen atom…
The molecule contains two hydrogen atoms, one sulphur atom and four oxygen atoms…
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
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:
O2, H2, HI, HCl, etc. Atomicity of them is TWO.
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.
Examples (molecule containing two atoms only):
1. CO2
2. NO
4. PCl3
3. PCl5
Carbon dioxide
Nitrogen monoxide
Phosphorus pentachloride
Phosphorus trichloride
Name of the first element: no change
Examples (molecule containing two atoms only):
1. CO2
2. NO
4. PCl3
3. PCl5
Carbon dioxide
Nitrogen monoxide
Phosphorus pentachloride
Phosphorus trichloride
Name of the first element: no change
Name of the second element: end with -ide
HCl : hydrogen chloride
N2O: dinitrogen oxide
More examples HF: hydrogen fluoride
SO2: sulphur dioxide
OCl2: oxygen dichloride
Sometimes, the prefix mono- is omitted
(simple hydrogen compounds)
(no. of atoms of the first element is more than one while the second has one atom only)
Carbon disulphide
Hydrogen fluoride
Sulphur hexachloride
Dinitrogen pentoxide
Sulphur trioxide
Phosphorus tribromide Hydrogen sulphide
Nitrogen monoxide
Carbon tetrachloride
Nitrogen dioxide
CS2
HF
N2O5
SO3
PBr3
SCl6
NO2
CCl4
NO
H2S
… 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.
Aluminium foil
If the atoms in a molecule are separated, the atoms formed will no longer have the properties of that substance.
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