how atoms react grade 9. its all about the electrons. every element has its own unique number of...
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How Atoms React
Grade 9
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Its all about the Electrons.
• Every element has its own unique number of protons = Atomic Number.
• Usually the number of protons is balanced by the number of electrons= neutral atom.
• Atoms want to achieve stability.• To achieve stability atoms need to complete
their electron orbits with the maximum number of electron allowed.
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Nobel Gases
• The Nobel Gases found on the far right of the periodic table all have completed electron orbits. They have the maximum number of electrons allowed in that orbit.
• Helium has 2 electrons, this fills this orbit and makes Helium a stable atom.
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Neon
Argon
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Alkali Metals
All Alkali metals have a single electron in an orbit.
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Achieving Stability
• In order to achieve stability atoms would like to have filled electron orbits.
• This means that atoms must:• Lose electrons• Gain electrons • Share electrons
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Valence Electrons
• The electrons found in the outmost orbit of an atom are known as Valence electrons.
• Valence electrons determine how many chemical bonds an atom will make in order to achieve stability.
• This is known as its bonding capacity.
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Metals
• Elements that have 1, 2 or 3 electrons in the outer orbits are metals
• Metals will lose their electrons in these orbits to achieve stability.
• When an atom loses electrons to achieve stability this upsets the balance of charges. There are now more positively charged protons in the nucleus than electrons orbiting that nucleus.
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Protons = 3+ + +
Electrons = 3- - -
If Lithium loses 1e-
This now leaves +++ and - -This creates an overall charge of
+1The Lithium atom is now known as an
+ve ION
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Cations
• Metals lose up to three electrons to become positively charged ions known as CATIONS.
Mnemonic device• Cations are paws-itive• Ca+ions ‘t’ looks like a ‘+’
Cations are pawsitive.
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Sodium Ion.
To identify an ion the atom or symbol is drawn inside parentheses (brackets).
[Na]+
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What happens to the size of the ion when an atom loses electrons?
Gets smaller
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Non –Metals
• Non- metals have 4,5,6 or 7 electrons in their valence orbits.
• Halogens (with 7 electrons) need only one more electron to complete their orbits.
• Halogens will form Negative IONS as they will now have 1 extra electron orbiting the nucleus
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Protons = 17+ + + + ++ + + + ++ + + + +
+ +
Electrons = 18- - - - - - - - - -- - - - -- - -
If Chlorine gains 1e-
This now leaves 17 + and 18-
This creates an overall charge of -1
The Chlorine atom is now known as an –ve ION
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Anions
• Non-metals that gain electrons form negative ions.
• Negative ions are known as ANIONS.Mnemonic device: ANION is A Negative Ion
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Chloride Ion
[Cl]-
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What happens to the size of the ion when an atom gains electrons?
Gets bigger
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Ionic BondsElements that lose or gain electrons from bonds known as IONIC bonds.Usually ionic bonds are formed between a metal and a non metal.
Sodium Chloride Magnesium Oxide
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Molecular/Covalent Bonds
• Non metals with 4 or more valence electrons can share pairs of electrons to complete the outermost orbits.
• These are known as COVALENT bonds• http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/atomic/covalentrev2.sht
ml
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H2 Cl2
O2
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