Polarisability
![]() All You Need in One PlaceEverything you need for better marks in primary, GCSE, and A-level classes. | ![]() Learn with ConfidenceWe’ve mastered the UK’s national curriculum so you can study with confidence. | ![]() Instant and Unlimited Help24/7 access to the best tips, walkthroughs, and practice questions. |
Make math click 🤔 and get better grades! 💯Join for Free
0/3
Intros
Lessons
0/0
Examples
Free to Join!
StudyPug is a learning help platform covering maths and science from primary all the way to second year university. Our video tutorials, unlimited practice problems, and step-by-step explanations provide you or your child with all the help you need to master concepts. On top of that, it's fun — with achievements, customizable avatars, and awards to keep you motivated.
Easily See Your Progress
We track the progress you've made on a topic so you know what you've done. From the course view you can easily see what topics have what and the progress you've made on them. Fill the rings to completely master that section or mouse over the icon to see more details.Make Use of Our Learning Aids
Earn Achievements as You Learn
Make the most of your time as you use StudyPug to help you achieve your goals. Earn fun little badges the more you watch, practice, and use our service.Create and Customize Your Avatar
Play with our fun little avatar builder to create and customize your own avatar on StudyPug. Choose your face, eye colour, hair colour and style, and background. Unlock more options the more you use StudyPug.
Topic Notes
In this lesson, we will learn:
- To understand why theoretical and experimental values for lattice energy are different.
- To explain how polarization leads to ionic bonds with covalent character.
- To understand the factors that affect the polarizability of anions in an ionic compound.
- When we calculate lattice energy for a compound, there is an issue to deal with. We can get two different values depending on how we find it.
- An experimental value that comes from Born-Haber cycles, calculated using enthalpy data (e.g. △Hf , ionization energy, atomization enthalpy) taken from experiments.
- A theoretical value which comes from electrostatic theory that explains how charges interact (Coulombic attraction).
- When we describe ionic bonding, the ions are often shown:
- Shaped like perfect spheres (or point charges) and
- Not making contact with each other.
- Remember, the cation polarises and the anion gets polarised, not the other way around!
- Polarising power: This is the ability of the cation to distort the anion’s electron cloud. This makes the bond more covalent in character and two factors make this effect stronger:
- Charge: the larger the charge, the more polarising the cation will be to any nearby negative ions.
- Ionic radius: the smaller the ionic radius, the higher the charge density which makes the cation’s polarising effect stronger.
- Polarisability: This is how easily the anion has its electron cloud distorted. More distortion creates a bond with more covalent character. Polarisability is affected by:
- Ionic radius: the larger the ionic radius, the greater the polarisability of an ion because electrons are held further from the positive nucleus they’re attracted to.
- This covalent character is seen in the difference between theoretical and experimental values for lattice enthalpy. The theory assumes perfect ionic bonding – the experimental reality, with covalent character, increases the lattice enthalpy. The gap between the two values follows a pattern with the gap in electronegativity between the two given ions in a compound - a gap in electronegativity is what drives ionic bonding in the first place!
If these values are different, then the theory does not describe the real ‘ionic’ lattice with 100% accuracy. This is because the bonding in the lattice is not 100% ionic!
There are two properties to know:
2
videos
remaining today
remaining today
5
practice questions
remaining today
remaining today