Chemical Bonding
Introduction to Chemical Bonding
This section reviews the fundamental concepts of chemical bonding as understood from O-level chemistry.
Ionic Bonds
Ionic bonds are formed between metals and non-metals.
Formation: A metal atom loses electrons to become a positively charged ion (cation), and a non-
metal atom gains these electrons to become a negatively charged ion (anion). The ionic bond is the
strong electrostatic attraction between these oppositely charged ions.
Structure: Ionic compounds form a crystal lattice structure, which is a giant, three-dimensional
arrangement of alternating positive and negative ions. Each ion is surrounded by several ions of the
opposite charge.
Properties:
High Melting and Boiling Points: A significant amount of energy is required to overcome the
strong electrostatic forces of attraction between the ions in the crystal lattice.
Dissolution: Ionic compounds typically dissolve in polar solvents like water but not in non-polar
organic solvents like ethanol.
Electrical Conductivity: They conduct electricity only when molten or dissolved in water, as the
ions are then free to move and carry charge. They do not conduct electricity in the solid state
because the ions are fixed in the lattice.
Factors Affecting Melting Point: Compounds with ions carrying higher charges (e.g., MgO with
Mg2+ and O2− ) have stronger electrostatic attractions and thus higher melting points compared to
compounds with singly charged ions (e.g., NaCl with Na+ and Cl− ).
Dot and Cross Diagrams for Ionic Compounds
Dot and cross diagrams illustrate the transfer of valence electrons. Different symbols (dots and crosses) are
used to distinguish electrons from different atoms.
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, Lithium Fluoride (LiF):
Lithium (Group 1) has 1 valence electron.
Fluorine (Group 7) has 7 valence electrons.
+
Lithium loses its valence electron to become Li .
−
Fluorine gains this electron to achieve a full outer shell, becoming F .
+ −
The diagram shows Li and F with the fluorine now having 8 valence electrons (7 of its own +
1 from Li).
Magnesium Oxide (MgO):
Magnesium (Group 2) has 2 valence electrons.
Oxygen (Group 6) has 6 valence electrons.
2+
Magnesium loses both valence electrons to become Mg .
2−
Oxygen gains these two electrons to achieve a full outer shell, becoming O .
2+ 2−
The diagram shows Mg and O with oxygen having 8 valence electrons.
Magnesium Chloride (MgCl2 ):
Magnesium (Group 2) has 2 valence electrons.
Chlorine (Group 7) has 7 valence electrons.
2+
Magnesium loses 2 electrons to become Mg .
Each chlorine atom gains 1 electron. Since magnesium loses 2 electrons, two chlorine atoms are
needed.
2+ −
The diagram shows Mg and two Cl ions, each with 8 valence electrons.
Sodium Oxide (Na2 O):
Sodium (Group 1) has 1 valence electron.
Oxygen (Group 6) has 6 valence electrons.
Oxygen needs 2 electrons. Each sodium atom can only donate 1 electron. Therefore, two
sodium atoms are required.
+ 2−
The diagram shows two Na ions and one O ion with 8 valence electrons.
Covalent Bonds
Covalent bonds are formed between two non-metal atoms.
Formation: Covalent bonds involve the sharing of one or more pairs of electrons between atoms to
achieve a stable, full outer electron shell. The bond is the strong attraction between the shared pair of
electrons and the positive nuclei of the bonded atoms.
Structure: Covalent compounds can exist as simple molecular structures or giant covalent structures.
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Introduction to Chemical Bonding
This section reviews the fundamental concepts of chemical bonding as understood from O-level chemistry.
Ionic Bonds
Ionic bonds are formed between metals and non-metals.
Formation: A metal atom loses electrons to become a positively charged ion (cation), and a non-
metal atom gains these electrons to become a negatively charged ion (anion). The ionic bond is the
strong electrostatic attraction between these oppositely charged ions.
Structure: Ionic compounds form a crystal lattice structure, which is a giant, three-dimensional
arrangement of alternating positive and negative ions. Each ion is surrounded by several ions of the
opposite charge.
Properties:
High Melting and Boiling Points: A significant amount of energy is required to overcome the
strong electrostatic forces of attraction between the ions in the crystal lattice.
Dissolution: Ionic compounds typically dissolve in polar solvents like water but not in non-polar
organic solvents like ethanol.
Electrical Conductivity: They conduct electricity only when molten or dissolved in water, as the
ions are then free to move and carry charge. They do not conduct electricity in the solid state
because the ions are fixed in the lattice.
Factors Affecting Melting Point: Compounds with ions carrying higher charges (e.g., MgO with
Mg2+ and O2− ) have stronger electrostatic attractions and thus higher melting points compared to
compounds with singly charged ions (e.g., NaCl with Na+ and Cl− ).
Dot and Cross Diagrams for Ionic Compounds
Dot and cross diagrams illustrate the transfer of valence electrons. Different symbols (dots and crosses) are
used to distinguish electrons from different atoms.
1/7
, Lithium Fluoride (LiF):
Lithium (Group 1) has 1 valence electron.
Fluorine (Group 7) has 7 valence electrons.
+
Lithium loses its valence electron to become Li .
−
Fluorine gains this electron to achieve a full outer shell, becoming F .
+ −
The diagram shows Li and F with the fluorine now having 8 valence electrons (7 of its own +
1 from Li).
Magnesium Oxide (MgO):
Magnesium (Group 2) has 2 valence electrons.
Oxygen (Group 6) has 6 valence electrons.
2+
Magnesium loses both valence electrons to become Mg .
2−
Oxygen gains these two electrons to achieve a full outer shell, becoming O .
2+ 2−
The diagram shows Mg and O with oxygen having 8 valence electrons.
Magnesium Chloride (MgCl2 ):
Magnesium (Group 2) has 2 valence electrons.
Chlorine (Group 7) has 7 valence electrons.
2+
Magnesium loses 2 electrons to become Mg .
Each chlorine atom gains 1 electron. Since magnesium loses 2 electrons, two chlorine atoms are
needed.
2+ −
The diagram shows Mg and two Cl ions, each with 8 valence electrons.
Sodium Oxide (Na2 O):
Sodium (Group 1) has 1 valence electron.
Oxygen (Group 6) has 6 valence electrons.
Oxygen needs 2 electrons. Each sodium atom can only donate 1 electron. Therefore, two
sodium atoms are required.
+ 2−
The diagram shows two Na ions and one O ion with 8 valence electrons.
Covalent Bonds
Covalent bonds are formed between two non-metal atoms.
Formation: Covalent bonds involve the sharing of one or more pairs of electrons between atoms to
achieve a stable, full outer electron shell. The bond is the strong attraction between the shared pair of
electrons and the positive nuclei of the bonded atoms.
Structure: Covalent compounds can exist as simple molecular structures or giant covalent structures.
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