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STRUCTURES Covalent and ionic substances have different structures which explains why they have different properties. IONIC STRUCTURE The ions in a solid are arranged so the ions of the same charge are not near each other. Ionic substances are made from IONS. The ionic bond is the attraction between the oppositely charged ions. Here is the structure of sodium chloride. Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + This regular repeating pattern of ions is called an IONIC LATTICE.
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STRUCTURESSTRUCTURES
BONDING, STRUCTURE BONDING, STRUCTURE & PROPERTIES& PROPERTIES
IONICIONIC COVALENTCOVALENT
After completing this topic you should be able to :
BONDING, STRUCTURE & BONDING, STRUCTURE & PROPERTIESPROPERTIES
STRUCTURESSTRUCTURES
• State an ionic structure consists of a giant lattice of oppositely charged ions.
• The formula for an ionic compound gives the simplest ratio of positive ions to negative ions.
• State covalent bonding can result in a molecular or giant network structure.
• Explain why discrete covalent substances have low melting and boiling points due to the weak forces of attraction that need to be overcome.
• Explain why ionic compounds and covalent network substances have high melting and boiling points due to the strong forces of attraction which need to be overcome.
STRUCTURESSTRUCTURESCovalent and ionic substances have different structures which explains why Covalent and ionic substances have different structures which explains why they have different properties. they have different properties.
IONIC STRUCTUREIONIC STRUCTURE
The ions in a solid are The ions in a solid are arranged so the ions of the arranged so the ions of the same charge are not near same charge are not near each other.each other.
Ionic substances are made from Ionic substances are made from IONSIONS. . The ionic bond is the attraction The ionic bond is the attraction between the oppositely charged ionsbetween the oppositely charged ions..
Here is the structure of Here is the structure of sodium chloride.sodium chloride.
NaNa++ ClCl-- NaNa++ ClCl--
ClCl-- NaNa++ ClCl-- NaNa++
NaNa++ ClCl-- NaNa++ ClCl--
ClCl-- NaNa++ ClCl-- NaNa++
NaNa++ClCl-- NaNa++ClCl--
ClCl--NaNa++ ClCl-- NaNa++
NaNa++ClCl-- NaNa++ClCl--
ClCl--NaNa++ ClCl-- NaNa++
NaNa++ ClCl-- NaNa++ ClCl--
ClCl-- NaNa++ ClCl-- NaNa++
NaNa++ ClCl-- NaNa++ ClCl--
ClCl-- NaNa++ ClCl-- NaNa++
This regular repeating This regular repeating pattern of ions is called pattern of ions is called an an IONIC LATTICEIONIC LATTICE. .
NaNa++
ClCl--
NaNa++
NaNa++
NaNa++
ClCl--
ClCl--
ClCl--
ClCl--
ClCl--
NaNa++
NaNa++
Each sodium ion, Na+ is Each sodium ion, Na+ is surrounded by 6 chloride surrounded by 6 chloride ions Cl- and vice versa. ions Cl- and vice versa.
There are equal numbers of sodium There are equal numbers of sodium and chloride ions in the ionic lattice.and chloride ions in the ionic lattice.
The ratio of The ratio of NaNa++ : : ClCl-- is 1 : 1. is 1 : 1.
This is why the formula is This is why the formula is NaNa++ClCl--. .
The formula of an ionic compound gives the ratio of the ions in the lattice.The formula of an ionic compound gives the ratio of the ions in the lattice.
The strong attraction between the ions takes a lot of energy to breakThe strong attraction between the ions takes a lot of energy to break. This . This is why all ionic compounds have high melting and boiling points and are is why all ionic compounds have high melting and boiling points and are solids at room temperature.solids at room temperature.
COVALENT STRUCTURE - MOLECULESCOVALENT STRUCTURE - MOLECULESMany covalent substances have low melting and boiling points.Many covalent substances have low melting and boiling points.
Covalent substances which have Covalent substances which have low melting and boiling points are low melting and boiling points are made from made from MOLECULESMOLECULES. .
DICTIONARY - DICTIONARY - MOLECULEMOLECULE
AA MOLECULE MOLECULE is a group of non – metal atoms joined together by covalent is a group of non – metal atoms joined together by covalent bonds.bonds.
The smallest molecule is made from two non - metal atoms. The largest The smallest molecule is made from two non - metal atoms. The largest are made from thousands of non – metal atoms.are made from thousands of non – metal atoms.
Oxygen molecule, Oxygen molecule, OO22(ELEMENT)(ELEMENT)
Methane molecule, Methane molecule, CHCH44(COMPOUND)(COMPOUND)
Polythene is a huge molecule Polythene is a huge molecule made from thousands of carbon made from thousands of carbon and hydrogen atoms.and hydrogen atoms.
The formula of a molecular The formula of a molecular substance actually tells you the type substance actually tells you the type of atoms and how many of each of atoms and how many of each atom is in the molecule. atom is in the molecule.
The atoms in a molecule are held together by strong covalent bonds.The atoms in a molecule are held together by strong covalent bonds.
There are only There are only weak forces weak forces of attractionof attraction BETWEEN BETWEEN MOLECULESMOLECULES. .
This means little energy is This means little energy is needed to make the water needed to make the water molecules move away from molecules move away from each other. each other.
Here is water as a solid, liquid and a gas. The three states of matter.Here is water as a solid, liquid and a gas. The three states of matter.
This is why the melting and This is why the melting and boiling points are low.boiling points are low.
The covalent bonds holding the H and O atoms together in each molecule The covalent bonds holding the H and O atoms together in each molecule are are NOT BROKEN NOT BROKEN in changing state.in changing state.
COVALENT STRUCTURE – NETWORK STRUCTURECOVALENT STRUCTURE – NETWORK STRUCTURESome covalent substances have very high melting and boiling points and are Some covalent substances have very high melting and boiling points and are very hard solids.very hard solids.
These covalent substances are not made from molecules.These covalent substances are not made from molecules.
They have a structure called a They have a structure called a COVALENT NETWORKCOVALENT NETWORK..
Diamond is made of carbon atoms and has a covalent Diamond is made of carbon atoms and has a covalent network structure.network structure.
Every carbon atom is bonded to 4 other carbons Every carbon atom is bonded to 4 other carbons which build up a huge network of atoms.which build up a huge network of atoms.
To melt the network requires the strong covalent To melt the network requires the strong covalent bonds to be broken. This means a huge amount of bonds to be broken. This means a huge amount of energy is required and the melting point is very high.energy is required and the melting point is very high.Structure of carbon Structure of carbon
as diamond.as diamond.
Silicon dioxide, SiO2 has a covalent network Silicon dioxide, SiO2 has a covalent network structure.structure.
Its formula shows the ratio of Si : O in the Its formula shows the ratio of Si : O in the network is 1 : 2.network is 1 : 2.
Granite is largely silicon dioxide.Granite is largely silicon dioxide.
Marischal College – Aberdeen City Council Headquarters is made of granite, Marischal College – Aberdeen City Council Headquarters is made of granite, i.e. silicon dioxide, SiOi.e. silicon dioxide, SiO22..
