Ionic bonding (AQA GCSE Chemistry Combined Science): Revision Notes
Ionic bonding
What is ionic bonding?
Ionic bonding happens when metals and non-metals react together. These bonds are very strong chemical connections that hold atoms together. When a metal meets a non-metal, they swap electrons to become more stable.
Ionic bonds are among the strongest types of chemical bonds. This is why ionic compounds like salt have high melting and boiling points - it takes a lot of energy to break these powerful attractions between oppositely charged ions.
How ions form
Positive ions (cations)
Metal atoms want to get rid of some electrons to become stable. When they lose electrons, they become positive ions called cations.
- Metal atoms have too many electrons in their outer shell
- They lose these extra electrons easily
- After losing electrons, they have more protons than electrons
- This makes them positively charged
Example: Sodium Ion Formation
Sodium atom: Na (11 protons, 11 electrons) ↓ loses 1 electron Sodium ion: Na (11 protons, 10 electrons)
The sodium atom loses one electron to achieve a stable electron configuration, becoming positively charged.
Negative ions (anions)
Non-metal atoms want to gain extra electrons to fill up their outer shell. When they gain electrons, they become negative ions called anions.
- Non-metal atoms need more electrons to fill their outer shell
- They grab electrons from metal atoms
- After gaining electrons, they have more electrons than protons
- This makes them negatively charged
Example: Chlorine Ion Formation
Chlorine atom: Cl (17 protons, 17 electrons) ↓ gains 1 electron Chloride ion: Cl (17 protons, 18 electrons)
The chlorine atom gains one electron to complete its outer shell, becoming negatively charged.
The electron transfer process
This is how ionic bonding actually works:
Complete Electron Transfer Process
- Metal atom starts with electrons it wants to lose
- Non-metal atom starts with empty spaces in its outer shell
- Electrons move from the metal to the non-metal
- Both atoms now have full outer shells (like noble gases)
- Opposite charges attract and the ions stick together
Worked Example with Magnesium and Oxygen:
- Magnesium atom loses 2 electrons → Mg ion
- Oxygen atom gains 2 electrons → O ion
- They attract each other to form magnesium oxide (MgO)
Patterns in the periodic table
Different groups of elements behave in predictable ways:
Critical Patterns to Learn:
Metals (Groups 1 and 2)
- Group 1 metals (like sodium) lose 1 electron → form 1+ ions
- Group 2 metals (like magnesium) lose 2 electrons → form 2+ ions
Non-metals (Groups 6 and 7)
- Group 7 non-metals (like chlorine) gain 1 electron → form 1- ions
- Group 6 non-metals (like oxygen) gain 2 electrons → form 2- ions
These patterns help you predict the charges of ions formed by different elements!
Noble gas structure
When atoms form ions, they try to get the same electron arrangement as noble gases. Noble gases are very stable because they have completely filled outer shells.
Why Noble Gas Structure Matters:
- Noble gases have 8 electrons in their outer shell (except helium which has 2)
- All other atoms want to copy this stable arrangement
- Losing or gaining electrons helps them achieve this goal
This is called the "octet rule" - atoms tend to gain, lose, or share electrons to achieve 8 electrons in their outer shell.
Key examples to remember
Example 1: Sodium Chloride Formation
Sodium and chlorine make sodium chloride (salt):
- Na loses 1 electron → Na
- Cl gains 1 electron → Cl
- Formula: NaCl
The 1:1 ratio occurs because both ions have equal but opposite charges.
Example 2: Magnesium Oxide Formation
Magnesium and oxygen make magnesium oxide:
- Mg loses 2 electrons → Mg
- O gains 2 electrons → O
- Formula: MgO
Again, a 1:1 ratio because the charges balance perfectly.
Summary
Key Points to Remember:
- Ionic bonds form when metals react with non-metals
- Metals lose electrons to become positive ions (cations)
- Non-metals gain electrons to become negative ions (anions)
- Electron transfer makes both atoms more stable with full outer shells
- Opposite charges attract to hold the ions together strongly
- Atoms aim for noble gas electron configurations through ion formation