Ionic BondingScience 10

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Keeping Track of Electrons• The electrons responsible for the chemical

properties of atoms are those in the outer energy level.

• Valence electrons – The electrons in the outer energy level (in valence shell).

• Kernel (core) electrons -those in the energy levels below the valence shell.

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Keeping Track of Electrons

• Atoms in the same column• Have the same number of outer electrons

(valence electrons).• Easily found by looking up the group number on

the periodic table.• Group 2 - Be, Mg, Ca, .- 2 valence electrons• The last digit in the representative group

number gives the number of valence electrons

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Electron Dot diagrams (Lewis Structure)

• A way of keeping track of valence electrons.

• How to write them• Write the symbol.• Put one dot for each valence

electron• Don’t pair up until they have

to

X

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The Electron Dot diagram for Nitrogen

Nitrogen has 5 valence electrons.

First we write the symbol.

NThen add 1 electron at a time to each side.Until they are forced to pair up.

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Write the electron dot diagram for

• Na• Mg• C• O• F• Ne• He

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Electron Configurations for Cations

• Metals lose electrons to attain noble gas configuration (Born losers).

• They make cations (positive ions).• If we look at electron configuration it

makes sense.• Na 2, 8, 1 - 1 valence electron• Na+ 2, 8 -noble gas configuration (Ne)

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Electron Dots For Cations• Metals will have very few valence electrons

Ca

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Electron Dots For Cations• Metals will have very few valence electrons• These will come off

Ca

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Electron Dots For Cations• Metals will have very few valence electrons• These will come off• Forming cations (positive ions)

Ca2+

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Electron Configurations for Anions

• Nonmetals gain electrons to attain noble gas configuration.

• They make anions (negative ions).• If we look at electron configuration it makes

sense.• S 2, 8, 6 - 6 valence electrons• S2- 2, 8, 8 -noble gas configuration (Ar).

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Electron Dots For Anions• Nonmetals will have many valence electrons.• They will gain electrons to fill outer shell.

P P3-

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Stable Electron Configurations• All atoms react to achieve noble gas

configuration.• Noble gases have 8 valence electrons .• Also called the octet rule.

Ar

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Ionic Bonding• Anions and cations are held together by

opposite charges.• Ionic compounds are called salts.• Simplest ratio is called the formula unit.• The bond is formed through the transfer of

electrons.• Electrons are transferred to achieve noble

gas configuration.

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Ionic Bonding

Na Cl

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Ionic Bonding

Na+ Cl-

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Counting ElectronsDuring the formation of an ionic compound the total

number of electrons lost (by metals in forming cations) must equal the total number of electrons gained (by anions).

Ca Group 2 loses 2 e-

P Group 15 (5A) gains 3e-

To keep totals equal a LCM of 6 is used.Therefore: 3 x Ca = 3 x 2+ = 6+

2 x P = 2 x 3- = 6-

6 lost (+6) = 6 gained (6-) Charges cancel.

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Ionic Bonding

• All the electrons must be accounted for, total lost = total gained!

Ca P

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Ionic Bonding

Ca P

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Ionic Bonding

Ca2+ P

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Ionic Bonding

Ca2+ P

Ca

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Ionic Bonding

Ca2+ P3-

Ca

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Ionic Bonding

Ca2+ P3-

Ca P

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Ionic Bonding

Ca2+ P3-

Ca2+ P

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Ionic Bonding

Ca2+ P3-

Ca2+ P

Ca

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Ionic Bonding

Ca2+ P3-

Ca2+ P

Ca

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Ionic Bonding

Ca2+ P3-

Ca2+P3-

Ca2+

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Ionic Bonding

Ca3P2

Formula Unit