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1.6 Bonding (B. Polarity (Describe polar covalent, non-polar covalent,…
1.6 Bonding
B. Polarity
Describe polar covalent, non-polar covalent, ionic and dative covalent bonds
A Dative covalent bond forms when the shared pair of electrons in the covalent bond come from only one of the bonding atoms. A dative covalent bond is also called co-ordinate bonding.
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Predict whether a compound of two or more elements would be covalent from the position of the elements in their periodic table or from their electronegativity values.
Electro-negativity is a measure of the ability of an atom to attract electrons. So electronegativity values can also be used to determine whether an ionic compound will result from two specific elements reacting together. It is generally recognized that a difference of 1.8 units or more on the Pauling scale will give a compound that is predominately ionic.
One element will usually be a metal on the left of the Periodic Table and the other a non-metal on the right. As well, we learned that the tendency to lose electrons and form positive ions increases down the groups on the left, whereas the tendency to gain electrons and form negative ion increase up the groups on the right.
Polar bonds result from unequal sharing of electrons. This occurs when there is a difference in the electronegativities of the bonded atoms, as the more electronegative atom exerts a greater pulling power on the shared electrons. The bond that is unsymmetrical with respect to electron distribution and is said to be polar. The term dipole is often used to indicate the fact that this type of bond has two separated opposite electric charges.
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A. Born-Haber Cycles
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Define electron affinity, atomisation and ionization energy.
Electron Affinity: the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.
Atomisation: The enthalpy change which accompanies the formation of one mole of gaseous atoms from the element under its standard state conditions.
Ionisation Energy: Standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a single positive charge.
List the properties of ionic crystals, and relate them to the lattice energy.
High Melting and Boiling point due to strong electrostatic attraction between the ions; High lattice energy leads to smaller atomic radius and strong electrostatic attraction.
Describe quantitatively the energetic factors and characteristics involved in the formation of an ionic bond.
The amount of energy needed to separate a gaseous ion pair is its bond energy. The formation of ionic compounds are usually extremely exothermic. The strength of the electrostatic attraction between ions with opposite charges is directly proportional to the magnitude of the charges on the ions and inversely proportional to the inter-nuclear distance.
Factors
Low ionisation energy of the metallic element, which forms the cation.
Low ionisation energy of the metallic element, which forms the cation.
Large lattice energy i.e., the smaller size and higher charge of the ions.
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