Ionic Bonding Flashcards
How are ionic bonds formed?
When one or more electrons are fully transferred between atoms
What kind of atoms does it occur between?
Metal and non-metal
What happens to the metal atoms in ionic bonding?
Try to attain the structure of a noble gas by losing electrons to form positive ions (cations)
What happens to non-metal atoms in ionic bonding?
Try to attain the structure of a noble gas by gaining electrons to form negative ions (anions)
What kind of attraction occurs between positive and negative ions in an ionic bond?
Electrostatic attraction
Describe the energy change in the formation of an ionic bond compared to the two isolated atoms
Decreases
What is the Octet rule?
Atoms tend to adjust their valence shells to 8 electrons by losing, gaining or sharing electrons
What are the exceptions to the Octet rule?
- Transition elements using d-orbitals obey the 18 electron rule instead
- Other elements with d-orbitals can accommodate more than 8 electrons
Describe the formation of an ionic bond
- Formation of ions: electrons transferred between metal and non-metal, one atom loses electrons and one atom gains electrons
- Electrostatic attraction between opposite charges
- Formation of an ionic compound
What is the definition of isoelectronic?
Two molecules/ atoms with the same number of valence electrons
What are the properties of an ionic bond?
- Non-directional
- Broken when compounds dissolve in polar solvents
- Structure breaks down when the compound is melted (conducts electricity when melted or in solution)
- Ionic compounds are not charged overall
How does an ionic lattice form?
Every ion is attracted to all other ions with the opposite charge, resulting in a repeating 3D pattern of anions and cations
What is enthalpy of formation?
Forming one mole of the ionic solid from its gaseous ions (measures bond strength)
What are the factors favouring ionic bonding?
- Easy cation formation
- Easy anion formation
- Large electronegativity difference between combining atoms
- High lattice energy of ionic compound
What is the trend between size positive charge of the ion and the size?
As the positive charge increases, the ion size decreases as the electrons can be pulled towards the positive nucleus more tightly
What is the trend between size of negative charge of the ion and the size?
As the charge of the ion gets more negative (electrons are added) the size of the ion increases because electron-electron repulsion increases causing the electron cloud to get bigger
What is polarisation?
Distortion of the electron cloud of an atom
What is polarising power?
An ions ability to distort the electron cloud of another atom
What happens to the polarising power as an atom decreases in size and its charge increases
Increases
What happens to the polarisability as an atom increases in size and its charge becomes more negative
Increases
Do cations or anions have more polarising power?
Cations (as they are smaller)
Are cations or anions more polarisable?
Anions
What is an ideal ionic compound?
Composed of completely separate spherical ions
What does polarisation result in?
Non-spherical ions and covalent character in the bond (stronger interaction on one side of the ion)
What do Fajan’s rules predict?
If there’s likely to be some covalent character in the bonding
How do we know if an ionic compound is likely to have some covalent character?
- The cation is small and/ or has a high charge
- The anion is large and/ or has a high charge
What is a polyatomic ions?
Ions that are made up of more than one type of atom
What type of bonding is present between polyatomics?
Covalent and the number of electrons means the group has an overall charge (so can form ionic bonds)
What are examples of important ions in the body and their function?
- Sodium and Potassium ions: signalling, producing electric currents required for nerve transmission and therefore muscle function
- Hydrogen ions: control of acid-base function and pH balance
- Phosphate ions: ATP synthesis
- Calcium Phosphate ions: skeleton
