Upload
benedict-fitzgerald
View
224
Download
0
Embed Size (px)
Citation preview
contentscontents
You will learn about:
• Ionic bonds – electron transfer
• Covalent bonds – electron sharing
• Properties of ionic and covalent compounds
You will learn about:
• Ionic bonds – electron transfer
• Covalent bonds – electron sharing
• Properties of ionic and covalent compounds
The noble gases
(Group 0 elements) are also known as inert gases. They are gases.
The noble gases
(Group 0 elements) are also known as inert gases. They are gases.
Noble Gas Electronic Configuration
1. When the outer shell of an element is completely filled with electrons, the element is very stable.
2. Atoms of noble gases in Group 0 are very stable. Hence, they do not react with other elements.
3. Noble gas configurations are very stable because they have fully filled outer/valence shells.
Noble gases (except for helium) have 8 electrons in their outer shells.
Noble gases (except for helium) have 8 electrons in their outer shells.
helium
neon
argon
He
Ne
Ar
Arrangement of electrons in the outer shell
Examples
2
2.8
2.8.8
Duplet structure
Octet structure
Octet structure
• The tendency for atoms to surround themselves with a stable ‘octet’ of electrons is called the octet rule.
• Helium has only 2 electrons in its outer shell , but is stable as it too has a fully filled outer shell of electrons.
The maximum number of electrons that can be accommodated in the 1st shell is 2. This is called the duplet rule.
Other elements do not have the stable electronic configuration where the outer shell is fully filled with electrons forming either the duplet or octet structure.
Thus, they react with one another by losing, gaining or sharing their valency electrons to achieve the stable noble gas electronic configuration during a chemical reaction.
( valency electrons are electrons in the outer shell used in chemical bonding)
Chemical bonding
Ionic bonding
Covalent bonding
By losing or gaining of electrons (i.e transferring of electrons)
Takes place between atoms of metals and non-metals
By sharing of electrons between atoms of non-metals
Covalent substances
Ionic compounds
An ion is a charged particle formed from an atom or a group of atoms by the loss or gain of electrons .It can be either positively or negatively charged.
atoms form ions by gaining or losing electrons to obtain the stable electronic structure of a noble gas
An ion is a charged particle formed from an atom or a group of atoms by the loss or gain of electrons .It can be either positively or negatively charged.
atoms form ions by gaining or losing electrons to obtain the stable electronic structure of a noble gas
Formation of Cations (positive ions) and Anions (negative ions)Formation of Cations (positive
ions) and Anions (negative ions)
negative ionadd
electrons
positive ion
neutral atom
remove electrons
electrons = protons
more electrons
than protons
more protons than
electrons
-
+
Electronic configuration of Metals & Non-metals• MetalsMetals tend to loselose their valence electrons to achieve
the stable noble gas electronic configuration as they have few valence electrons.
• Non-metalsNon-metals tend to gaingain electrons to achieve the stable noble gas electronic configuration as they have a lot of electrons in their valence shell
Note : only the valence (outer) electrons are involved in bonding; those in the complete inner shells do not take part.
Na atom 2,8,1 Na+
ion2,8
Na atom loses an electron and becomes a positive ion, sodium ion, Na+ which have the stable noble gas electronic structure as Neon (2,8).
11 protons11 electrons12 neutrons
11 protons10 electrons12 neutrons
loses 1 electron
+
Na Na
[all +ve charges (protons) balanced by -ve charges (electrons)]
11 protons (+11) and
10 electrons (-10)
overall charge = (+11 -10) = +1
NeutralCharged (+1)
Al atom 2,8,3 Al3+ ion 2,8
Al atom loses 3 electrons and becomes a positive ion, aluminium ion, Al3+ which have the stable noble gas electronic structure as Neon (2,8).
13 protons13 electrons14 neutrons
13 protons10 electrons14 neutrons
loses 3 electrons
3+
Al Al
[all +ve charges (protons) balanced by -ve charges (electrons)]
13 protons (+13) and
10 electrons (-10)
overall charge = (+13 -10) = +3
NeutralCharged (+3)
Formation of AnionsCl atom gains 1 electron from a metal atom and becomes a negative ion,
named as chloride ion, Cl- which has the same noble gas electronic structure as Argon (2,8,8).
17 protons17 electrons18 neutrons
17 protons18 electrons18 neutrons
chlorine atom2,8,7
Cl
chloride ion2,8,8
gains 1 electronx
¯
Cl
Charged (-1)
17 protons (+17) and
18 electrons (-18)
overall charge = (+17 -18) = -1
Neutral
Now You Try ………
Draw diagrams to show the formation of (a)a fluoride ion (b) an oxide ion (c) a nitride ion
Cations- more examples
12 10 19 18Number of electrons
20191212No of protons
Mg Mg2+ K K+Symbol
Magnesium Magnesium atomatom
MagnesiumMagnesiumionion
PotassiumPotassiumatomatom
PotassiumPotassiumatomatom
Number of neutrons
12 12 20 20
2412 12
24 39
193919
Note: A positive ion still has the same number of protons
and neutrons as its atom, but, it will have less
electrons than protons.
16 16 8 8Number of neutrons
Anions – more examples
SulphurSulphuratomatom
Sulphide Sulphide ionion
Oxygen Oxygen atomatom
Oxide Oxide ionion
881616No of protons
S S2- O O2-Symbol
16 18 8 10Number of electrons
32 3216 16
16 168 8
Note: A negative ion still has the same number of
protons and neutrons as its atom, but, it will
have more electrons than protons.
Ionic bonding – involves the transfer of electrons from one atom to another so that each can achieve the noble gas electronic configuration.
Ionic bonding – involves the transfer of electrons from one atom to another so that each can achieve the noble gas electronic configuration.
usually formed between atoms of metals and non-metals
positive and negative ions are formed after the transfer of electrons
The oppositely charged ions are attracted to each other by strong electrostatic force of attraction.
This strong electrostatic force of attraction between the oppositely charged ions is called ionic bond.
Example
Example 1 Formation of sodium chloride through ionic bonding
sodium atom, Na2.8.1
chlorine atom, Cl2.8.7
electron transfer
Diagrammatic Representation of Ionic BondingDiagrammatic Representation of Ionic Bonding
An ionic compound, sodium chloride ( NaCl ) is formed. An ionic compound, sodium chloride ( NaCl ) is formed.
has the same electronic structure as
the noble gas, neon
has the same electronic structure as the noble gas, argon
sodium ion, Na+
2.8
++
chlorine ion, Cl-
2.8.8
--
Na Cl
‘DOT and CROSS’ Diagram
- electron
of Na
- electron
of Cl
Example 2 Formation of magnesium chloride
through ionic bonding
Example 2 Formation of magnesium chloride
through ionic bonding
chlorine atom, Cl
2.8.7
electron transfer
ionic bonds – electron transferionic bonds – electron transfer
chlorine atom, Cl
2.8.7
electron transfer
magnesium atom, Mg
2.8.2
Mg
ClCl
ionic bonds – electron transferionic bonds – electron transfer
has the same electronic structure as
the noble gas, neon
has the same electronic structure as the noble gas, argon
magnesium ion, Mg2+
2.8
2+2+
chloride ion, Cl-
2.8.8
--
has the same electronic structure as the noble gas, argon
chloride ion, Cl-
2.8.8
--
Cl Mg Cl
Ionic bonds are formed between atoms of metals and non-metals in compounds.
Examples include:
Ionic bonds are formed between atoms of metals and non-metals in compounds.
Examples include:
ionic bondsionic bonds
Compounds with ionic Compounds with ionic bondsbonds ElementsElements
NameName FormulaFormula MetalsMetals Non-Non-metalsmetals
sodium chloride
NaCl sodium chlorine
magnesium oxide
MgO magnesium oxygen
potassium iodide
KI potassium iodine
calcium bromide
CaBr2 calcium bromine
Structures of Ionic CompoundsStructures of Ionic Compounds
Ionic compounds have giant ionic lattice structure.
Properties of ionic compoundsProperties of ionic compounds
Have high melting points (above 250oC) and high boiling points (above 500oC)
Reason: The ionic bonds (electrostatic force of attraction) between the ions are very strong . A very large amount of heat energy is needed to overcome these strong bonds.
This also explains why all ionic
compounds are solids at
room temperature.
Have high melting points (above 250oC) and high boiling points (above 500oC)
Reason: The ionic bonds (electrostatic force of attraction) between the ions are very strong . A very large amount of heat energy is needed to overcome these strong bonds.
This also explains why all ionic
compounds are solids at
room temperature.
I. Boiling points and Melting PointsI. Boiling points and Melting Points
++++
++++
++++
++++
++++
++
++
-- -- --
-- -- --
-- -- --
-- --
-- --
II. Solubility II. Solubility
Ionic compounds are usually soluble in water but insoluble in organic solvents.
Reason: water molecules can separate the positive ions from the negative ions, causing them to dissolve.
Exceptions: silver chloride, barium sulphate are ionic compounds which are insoluble in water.
Organic solvents eg petrol, alcohol and turpentine
Ionic compounds are usually soluble in water but insoluble in organic solvents.
Reason: water molecules can separate the positive ions from the negative ions, causing them to dissolve.
Exceptions: silver chloride, barium sulphate are ionic compounds which are insoluble in water.
Organic solvents eg petrol, alcohol and turpentine
properties of ionic compoundsproperties of ionic compounds
Ionic compounds do not conduct electricity in the solid state because the ions are not free to move about.
When the substance is in molten state (melted in liquid form)) or aqueous state ( when dissolved in water), it can conduct electricity.
Reason : In these states, the ions are free to move. The moving ions conduct electricity.
Ionic compounds do not conduct electricity in the solid state because the ions are not free to move about.
When the substance is in molten state (melted in liquid form)) or aqueous state ( when dissolved in water), it can conduct electricity.
Reason : In these states, the ions are free to move. The moving ions conduct electricity.
III Electrical conductivityIII Electrical conductivity
Covalent bond is a bond formed by the sharing of electrons between atoms of non-metals.
After bonding, each atom attains the stable noble gas electronic configuration.
Covalent bond is a bond formed by the sharing of electrons between atoms of non-metals.
After bonding, each atom attains the stable noble gas electronic configuration.
What is covalent bond?What is covalent bond?
Why must atoms of non-metals share electrons while atoms of metals and non-metals form ions?
Why covalent bonds are formed between non-metal atoms?
• For elements with 4 valency electrons, gaining or losing 4 electrons to achieve a noble gas electronic configuration requires a large amount of energy. Thus, the non-metallic elements combined by sharing of electrons to form molecules.
Valency electrons - are electrons in the outermost
shell used to form bonds.
Valency - is the number of electrons an atom uses to
form bonds
Valence electrons - are electrons in the outermost shell
The molecules formed can be
(i) Simple covalent molecules like H2, O2, H2O, CO2, NH3, CH4, HCl, N2, Cl2, etc or
(ii)Giant covalent molecules (or macromolecules)( which is a three dimensional network of atoms bonded together by covalent bonds to form a giant molecule ) like diamond, graphite, silicon dioxide, etc
Covalent Covalent MoleculeMolecule
Chemical Chemical formulaformula
Electronic Structure of Molecule Electronic Structure of Molecule (‘Dot and Cross’ Diagram)(‘Dot and Cross’ Diagram)
Structural Structural diagramdiagram
hydrogen gas H2
Other ways to represent :
H H
H H+
H atom H atom
H H
H2 molecule
H H
Formation of Covalent Bonds Formation of Covalent Bonds
x
o
Single covalent bond
Covalent Covalent MoleculeMolecule FormulaFormula Electronic Structure of Molecule Electronic Structure of Molecule
(‘Dot and Cross’ Diagram)(‘Dot and Cross’ Diagram)
Simple Way of Simple Way of Showing the Showing the
BondsBonds
water H2OH
H
OH
O
H
Other ways to rep :
or H O
xx
xx xx H
Covalent Covalent MoleculeMolecule FormulaFormula Electronic Structure of Molecule Electronic Structure of Molecule
(‘Dot and Cross’ Diagram)(‘Dot and Cross’ Diagram)
Simple Way of Simple Way of Showing the Showing the
BondsBonds
methane CH4H
H
C H
H
H C
H
H
H
Other ways to rep :
orx
x
xx HH C
H
H
Covalent Covalent MoleculeMolecule FormulaFormula Electronic Structure of Molecule Electronic Structure of Molecule
(‘Dot and Cross’ Diagram)(‘Dot and Cross’ Diagram)
Simple Way of Simple Way of Showing the Showing the
BondsBonds
carbon dioxide
CO2
O C OOCO
Other ways to rep :
x xo ox x or x O xoC ox O x xx xx
Covalent Covalent MoleculeMolecule FormulaFormula Electronic Structure of Molecule Electronic Structure of Molecule
(‘Dot and Cross’ Diagram)(‘Dot and Cross’ Diagram)Structural Structural diagramdiagram
oxygen O2
O OOO
Other ways to rep : x x o o
or xo O xo O x x o o
Double bond
(2 pairs of electrons)
Covalent Covalent MoleculeMolecule
FormulaFormula Electronic Structure of Molecule Electronic Structure of Molecule (‘Dot and Cross’ Diagram)(‘Dot and Cross’ Diagram)
Structural Structural diagramdiagram
nitrogen N2
N NNN
Other ways to rep : x x o o
or xo N xo N xo
Triplebond
(3 pairs of electrons)
Example 1 :Iodine is a simple diatomic covalent molecule.
It has a simple molecular structure.
Reason : There exists weak intermolecular forces of attraction, between the iodine molecules, also known as weak Van der Waals’ forces. These weak forces of attraction requires only a small amount of heat enerrgy to overcome.
Example 1 :Iodine is a simple diatomic covalent molecule.
It has a simple molecular structure.
Reason : There exists weak intermolecular forces of attraction, between the iodine molecules, also known as weak Van der Waals’ forces. These weak forces of attraction requires only a small amount of heat enerrgy to overcome.
(a) Simple Molecular Structure(a) Simple Molecular Structure
Structure of Covalent SubstancesStructure of Covalent Substances
Example 2 Methane is also a simple covalent molecule.
Four covalent bonds (C-H) are held together by strong forces of attraction. However, weak Van der Waals’ forces between methane molecules hold them together loosely. Therefore, methane exists as a gas at room temperature and pressure.
Example 2 Methane is also a simple covalent molecule.
Four covalent bonds (C-H) are held together by strong forces of attraction. However, weak Van der Waals’ forces between methane molecules hold them together loosely. Therefore, methane exists as a gas at room temperature and pressure.
Covalent molecules have strong covalent bonds between atoms, but the Van der Waals’ forces which exist between separate molecules are weak.
During melting or boiling, the molecules do not break up into atoms, but merely move further apart.
Thus, simple covalent molecules are volatile, i.e., they have low melting points and boiling points, as not much heat energy is needed to overcome the Van der Waals’ forces.
Covalent molecules have strong covalent bonds between atoms, but the Van der Waals’ forces which exist between separate molecules are weak.
During melting or boiling, the molecules do not break up into atoms, but merely move further apart.
Thus, simple covalent molecules are volatile, i.e., they have low melting points and boiling points, as not much heat energy is needed to overcome the Van der Waals’ forces.
volatilityvolatility
Properties of simple covalent compounds
Properties of simple covalent compounds
Molecules do not break up into atoms but merely move further apart during melting
and boiling
Most covalent molecules are insoluble in water but are usually soluble in organic solvents.
Exceptions: Alcohol and sugar are covalent compounds which are soluble in water.
Some covalent molecules dissolve in water because of chemical reactions. E.g., chlorine.
Most covalent molecules are insoluble in water but are usually soluble in organic solvents.
Exceptions: Alcohol and sugar are covalent compounds which are soluble in water.
Some covalent molecules dissolve in water because of chemical reactions. E.g., chlorine.
solubilitysolubility
Properties of simple covalent compounds
Properties of simple covalent compounds
Covalent substances (elements or compounds) do not conduct electricity whether in the solid or molten state. This is because they do not contain ions or free electrons.
Exceptions: carbon, in the form of graphite, conducts electricity. Covalent compounds such as hydrogen chloride and hydrogen sulphide also conduct electricity when dissolved in water.
Covalent substances (elements or compounds) do not conduct electricity whether in the solid or molten state. This is because they do not contain ions or free electrons.
Exceptions: carbon, in the form of graphite, conducts electricity. Covalent compounds such as hydrogen chloride and hydrogen sulphide also conduct electricity when dissolved in water.
electrical conductivityelectrical conductivity
Differences between Ionic and Covalent Bonding
Differences between Ionic and Covalent Bonding
Ionic Bond Covalent Bond
•Formed between metals and non-metals.
•Formed by transferring of electrons.
•Formed between non-metals and non-metals.
•Formed by sharing of electrons.
properties of ionic and covalent compounds
properties of ionic and covalent compounds
PropertyProperty Ionic CompoundsIonic CompoundsCovalent Compounds Covalent Compounds
(with simple (with simple Molecular Structure)Molecular Structure)
Boiling point high low
Electrical conductivity
do not conduct electricity when solid; conduct when
molten or dissolved in water
do not conduct electricity in any form
Solubility in Water
usually soluble usually insoluble
Solubility in organic solvents
insoluble soluble
summary of main differences in properties between ionic compounds and covalent compounds
summary of main differences in properties between ionic compounds and covalent compounds