Formadon of Ions

Forma&on of Ions Forma&on of Ions Elements tend to lose or gain electrons to fill their outermost energy levels with eight electrons depending on their electron affinity •  As a general rule, metals will give electrons away and nonmetals will accept electrons. • 
•  Octet rule: atoms tend to gain, lose or share electrons so as to have eight electrons in their outer electron shell –  AAain Noble Gas Status •  Sodium: 1s2 2s2 2p6 3s1 [Ne] 3s1 •  Chlorine: 1s2 2s2 2p6 3s2 3P5 [Ne] 3s2 3P5 Forma&on of Ions Causes an imbalance of charge (more or less electrons than protons) •  This imbalance in the element is called “ionizing”, and the element is transformed into an “ion” • 
Forma&on of Ions • 
The charge of an ion can be computed by subtrac&ng the number of protons by the new number of electrons: Chlorine would gain 1 electrons so: 17 -­‐ 18 = -­‐1 charge n 
Forma&on of Ions Sodium would lose 1 electrons so: 11 -­‐ 10 = +1 n 
• 
An ion and its charge is represented by the element's symbol and then the charge is wriAen aZer it as a superscript: +1
Na
-1
Cl
Forma&on of Ions The general term for a posi&ve ion is a ca#on. •  The general term for a nega&ve ion is an anion. • 
Forma&on of Ions • 
Remembering the Periodic Law will help you realize that all of the elements in each column will have the same charge as an ion: Forma&on of Ions • Na = Na+1 • K = K+1 • Li = Li+1 • and so on Forma&on of Ions • 
Unfortunately, since the transi&on metals have only two electrons in their outermost energy level, we cannot use the Rule of Eight to determine their ionic charge. Forma&on of Ions • 
To accommodate this, we will assume that an ion of a transi&on metal will be +2 unless otherwise stated (they have the ability to have more than one oxida&on number). Ionic Compounds Ionic Compounds •  Ionic compounds are made up by the
chemical combination of metallic and
non-metallic elements.
•  Most rocks, minerals and gemstones are
ionic compounds.
•  Ceramics, bricks and kitchen crockery are
made from clays which contain ionic
compounds.
•  While most of the above are made up of
mixtures of different ionic compounds table
salt is a pure ionic compound made up of
sodium chloride (NaCl)
Proper&es of Ionic Compounds •  Think of the properties of rocks, bricks,
crockery and table salt. What properties do
they share?
–  Have high melting and boiling temperatures.
–  Are hard but brittle
•  They also:
–  Do NOT conduct electricity in the solid state
–  They will only conduct electricity if they are
melted or dissolved in water
Structure of ionic compounds •  The physical properties of ionic
compounds are very different from
metals.
•  The structure of ionic compounds must
therefore be very different from those
present in metals.
•  What do we already know about ionic
compounds.
What do the proper&es tell us? Structure •  From the properties we can conclude:
–  The forces between the particles are
strong.
–  There are no free-moving electrons
present, unlike in metals.
–  There are charged particles present, but
in solid state they are not free to move.
–  When an ionic compound melts, however,
the particles are free to move and the
compound will conduct electricity.
The ionic bonding model •  Metal atoms lose electrons to non-­‐metallic atoms and become posi&vely charged metal ions. •  Non-­‐metal atoms gain electrons from the metal atoms and so become nega&vely charged non-­‐metal ions. •  Large numbers of posi&ve and nega&ve ions formed in this way then combine to form a three-­‐dimensional ladce. •  The three dimensional ladce is held together strongly by electrosta&c forces of aArac&on between posi&ve and nega&ve ions. This electrosta&c force is called ionic bonding. How many chlorine ions surround
each sodium ion and vice versa?
Using the ionic bonding model to explain the proper&es of sodium chloride High Mel&ng Temperature •  Ever no&ced that when you eat french fries the food may be hot but the salt does not melt. •  This is because to melt and ionic solid energy must be provided to allow the ions to break free and move. •  NaCl has a high mel&ng temp, this indicates a large amount of energy is needed to reduce the electrosta&c aArac&on between the oppositely charged ions and allow them to move freely. Hardness and BriAleness •  Unlike metals ionic compounds are not
malleable. They break when beaten.
•  A force can disrupt the strong electrostatic
forces holding the lattice in place.
•  A sodium chloride crystal cannot be
scratched easily but if a strong force (a
hammer blow) is applied it will shatter.
•  This is because the layers of ions will move
relative to each other due to the force.
•  During this movement, ions of like charge
will become adjacent to each other.
Resulting in repulsion
Hardness and BriAleness §  Figure 6.4 The repulsion
between like charges causes
this sodium chloride crystal to
shatter when it is hit sharply.
Electrical Conduc&vity •  In the solid form, ions in sodium chloride are
held in the crystal lattice and are not free to
move so cannot conduct electricity.
•  When the solid melts the ions are free to
move.
•  The movement of these charged particles to
an electrode completes an electrical circuit.
•  In a similar way, when sodium chloride
dissolves in water, the ions separate and are
free to move towards the opposite charge.
Reac&ons of metals with non-­‐metals •  Metallic atoms have low ionization
energies and low electronegativities.
•  Non-metallic atoms have high
ionization energies and low
electronegativities.
•  In other words metallic atoms lose
electrons easily and non-metallic
atoms gain electrons easily.
Ionic Compounds •  So the metal atoms lose an electron to
the non-metal atoms.
•  In doing so, both atoms will often
achieve the electronic configuration
of the nearest noblest gas, which is
particularly stable.
Sodium Chloride •  When sodium reacts with chlorine:
•  Na atom (1s2 2s2 2p6 3s1) loses an
electron to become 1s2 2s2 2p6 (the
same as Neon)
•  Cl atom (1s2 2s2 2p6 3s1 3p5) gains an
electron to become 1s2 2s2 2p6 3s1 3p6
(the same as argon)
Magnesium Oxide •  What are the electron configurations
for Magnesium and Oxygen?
•  How many electrons does
magnesium need to lose to get a full
outer shell?
•  How many electrons does oxygen
need to gain to get a full outer shell?
•  Draw an electron transfer diagram.
•  What is the electrovalency of a
magnesium ion and an oxide ion?
Magnesium Chloride •  What are the electron configurations
for Mg and Cl?
•  So a Mg atom will have a stable outer
shell if 2 electrons are removed.
•  A Cl atom only needs to gain one
electron.
•  So how can this work?
http://www.yenka.com/freecontent/item.action?quick=so#
Chemical Formulas •  Almost every compound in which a
metal is combined with a non-metal
displays ionic bonding.
•  The formulas of simple ionic
compounds, such as NaCl and MgCl2
can be predicted from the electron
configurations of the atoms.
Wri&ng Formulas: Rules •  Chemical formulas are part of the
language of chemists. To understand
and use this language, you need to
follow a number of fules.
Wri&ng Formulas: Rules Simple Ions •  The posi&ve ion is place first in the formula, the nega&ve ion is second. •  For example: KF, CuO •  Posi&ve and nega&ve ions are combined so that the total number of posi&ve charges is balanced by the total number of nega&ve charges. •  For example, CuS, CuCl2, AlCl3 and Al2O3 •  When there are two or more of a par&cular ion in a compound, then in the chemical formula the number is wriAen as a subscript aZer the chemical symbol. For example, Al2O3 Polyatomic ions •  Some ions contain more than one atom.
•  These are called polyatomic ions.
–  nitrate (NO3-) and hydroxide (OH-).
•  If more than one of these ions is used to
balance the charge of a compound, then it
is placed in brackets with the required
number written as a subscript after the
brackets.
For example Mg(NO3)2 and Al(OH)3
•  Brackets are not required for the formula of
sodium nitrate NaNO3, where there is only
one nitrate ion present for each sodium ion.
Different Electrovalencies •  Some elements form ions with different
charges.
•  Iron ions can have a charge of +2 or +3.
•  In this situation you need to specify the
electrovalency when naming the
compound.
•  This is done by placing a Roman numeral
representing the electrovalency of the ion
immediately after the metal in the name of
the compound.
•  For example
•  Iron(II) chloride contains Fe2+ ions and so the
formula is FeCl2
•  Iron(III) chloride contains Fe3+ ions and so the
forumla is FeCl3
Metallic Bonds Ca&ons packed in “a sea of electrons” Metals •  Metals consist of closely packed
cations floating in a “sea of
electrons”.
•  Delocalized electrons
•  All of the atoms are able to share the
electrons.
•  The electrons are not bound to
individual atoms.
Proper&es of Metals •  Good conductors
•  Ductile
•  Malleable
•  Electrons act as a lubricant, allowing
cations to move past each other
Metals have a Crystalline Structure •  Packed spheres of the same size and
shape:
– Body Centered Cubic
– Face Centered Cubic
– Hexagonal Close Packed
Body Centered Cubic Chromium
Face-­‐Centered Cubic Gold
Hexagonal Close-­‐Packed http://phycomp.technion.ac.il/~pavelba/hcpS.gif
Zinc
Alloys •  Mixtures of two or more elements, at
least one of which is a metal.
•  Made by melting, mixing, then cooling
the metals.
•  May contain non-metals like carbon.
Alloys •  Properties are superior to their
components.
•  Sterling silver
–  92.5% Ag, 7.5% Cu
–  Harder than silver
•  Bronze
–  7:1 Cu to Sn (tin)
Alloys •  Stainless Steel
– Fe 80.6%, Cr 18%, C 0.4%, Ni 1%
•  Cast Iron
-Fe 96%, C 4%
Types of Alloys •  Two types of formation:
– Substitutional alloys
• Similar size atoms – replacement
– Interstitial alloys
• Different size atoms – smaller ions
fill interstices (spaces between
atoms)