SNC 2P/SCH 3U/SCH 4C/SCH 4U - Chemistry - Valences

Valences

A valence is the real or apparent charge on an atom in a compound.

Grab a fresh Periodic Table and several coloured pencils and let's get cracking.

 

This chart is also useful for determining valences.

 

 

SNC 2P - Chemistry - Ionic Bonding

Ionic Bonding

When a metal reacts with non-metal, electrons are transferred from the metal to the non-metal. 

The atoms of the metal, having lost electrons, become positively charged ions.

The atoms of the non-metal, having gained electrons, become negatively charged ions.

These oppositely charged ions attract each other and ionic bond is formed.

The resulting molecule is neutral.  

ex. NaCl

• Na has 1 electron in its valence shell - Na loses 1 electron - Na takes on a + charge.
  
• Cl has 7 electrons in its valence shell - Cl gains one electron - Cl takes on a - charge.
• notice that the number of electrons lost by a single Na and the number of electrons gained by a Cl matches perfectly, producing a neutral compound (NaCl).
  

  

 

ex. Ca₃N₂

• Ca has 2 electrons in its valence shell - Ca loses 2 electrons - Ca takes on a 2+ charge.
• N has 5 electrons in its valence shell - N gains 3 electrons - N takes on a 3- charge.
  
• notice that the number of electrons lost by a single Ca and the number of electrons gained by a single N does not match, so we require multiple of each element.
• the total number of electrons lost by all the Ca (2 + 2 + 2 = 6) matches the total number of electrons gained by all the N (3 + 3 = 6),, producing a neutral compound (Ca₃N₂).

 

Conductivity of Ionic Compounds

A physical property that can be used to qualitatively analyze if a substance is an electrolyte (ionic) or a non-electrolyte.

Check out this video.

Homework:

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SNC 2P - Chemistry - Ions

Ions

An ion is a charged particle formed when an atom loses or gains electrons.

Atoms lose or gain electrons to attain a full outer shell like the Noble Gases (this is known as the Octet Rule).

 

Metals

When atoms lose electrons, there are now more protons than electrons, so the ion has a positive charge.  Typically, metals lose electrons to attain a full outer shell.

 Potassium

• starts with 1 electron in its outer shell
• it could gain 7 electrons or lose 1 electron to attain a full outer shell
• it makes more sense to lose 1 electron
• this gives potassium a positive charge (+)

Magnesium

• starts with 2 electrons in its outer shell
• it could gain 6 electrons or lose 2 electrons to attain a full outer shell
• it makes more sense to lose 2 electrons
• this gives magneisum a positive charge (2+)

 

Non-metals

When atoms gain electrons, there are now more electrons than protons, so the ion has a negative charge.  Typically, non-metals gain electrons to attain a full outer shell.

Chlorine

• starts with 7 electrons in its outer shell
• it could gain 1 electron or lose 7 electrons to attain a full outer shell
• it makes more sense to gain 1 electron
• this gives chlorine a negative charge (-)

Phosphorus

• starts with 5 electrons in its outer shell
• it could gain 3 electrons or lose 5 electrons to attain a full outer shell
• it makes more sense to gain 3 electrons
• this gives phosphorus a negative charge (3-)

 

Isoelectronic

Two particles are said to be isoelectronic if they have the same number of electrons. Typically, we will find out with which Noble Gas the ion is isoelectronic.

Looking at the ions above:

• K⁺ is isoelectronic with Ar (since both K⁺ & Ar have 18 total electrons)
  
• Mg²⁺ is isoelectronic with Ne (since both Mg²⁺ & Ne have 10 total electrons)
• Cl^- is isoelectronic with Ar (since both Cl^- & Ar have 18 total electrons)
• P^3- is isoelectronic with Ar (since both P^3- & Ar have 18 total electrons)

Question of the Day #14:  

For sulfur and lithium:

(a)  Draw the Lewis diagram for each atom.

(b)  Draw the Lewis diagram for each ion.

(c)  Indicate with which Nobel Gas each ion is isoelectronic.

 

Homework: 

 

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