4. Chemical Bonding & Structure Flashcards
Are metals cations or anions?
Cations
Describe the four properties of ionic compounds.
- High melting point- lots of energy required to break strong electrostatic forces.
- Crystalline- ions have a regular arrangement in their lattice.
- Conduct electricity when molten or solid- ions are free to move.
- Brittle- small displacement of lattice causes like ions to align and repel.
Define ‘ionic bond’.
The electrostatic force of attraction between oppositely charged ions.
What type of ions will have the greatest force of electrostatic attraction?
Small ions with a large charge.
Define ‘metallic bond’.
Positive metal cations are attracted to delocalised electrons by strong electrostatic forces.
What is the structure of a metallic structure?
Giant 3D crystal lattice
Describe the four properties of metallic bonds.
- High melting point- cations are held to electrons by strong electrostatic forces.
- Malleable and ductile- ions are glued into new positions by delocalised electrons.
- Conduct electricity- delocalised electrons are free to move in a given direction.
- Conductor of heat- ions are closely packed, so vibrations transfer easily.
Define ‘covalent bond’.
A pair of shared electrons.
What is a co-ordinate bond?
- A type of bond formed when both electrons come from the same atom.
- The lone pair of electrons help to fill the other atom’s outer shell.
How is a co-ordinate bond represented?
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What is the electronegativity difference for a polar bond?
At least 0.5
What are the three types of intermolecular force?
- London dispersion forces
- Dipole-dipole forces.
- Hydrogen bonding.
Describe the features of London dispersion forces.
- Present between all molecules and atoms.
- Instantaneous dipole forms
- Very weak
Describe how an instantaneous dipole forms.
The electrons are constantly moving, causing one side of the molecule to be slightly charged. This causes the other molecule to be instantaneously attracted.
Describe the features of dipole-dipole forces.
- Some unsymmetrical molecules have permanent dipoles.
- The permanently negative end of one molecule is attracted to the permanently positive end of the other molecule.
- Approximately 1% the strength of a covalent bond.
Describe the features of hydrogen bonding.
- A type of permanent dipoles due to permanent dipole force.
- About 10% strength of a covalent bond.
- H must be bonded to N, O or F.
Describe the features of a giant molecular structure.
- High melting point- many covalent bonds needed to break.
- Don’t conduct electricity (except graphite)- no free ions/ electrons.
- Hard- exists in a tetrahedral structure.
Describe the features of diamond
- Very high melting point- covalent bonds must be broken.
- Very strong- each carbon is joined to 4 other carbons.
- Doesn’t conduct electricity- no free electrons.
Describe the features of graphite.
- Very high melting point.
- Soft- layers are held by weak London forces which can slide over each other.
- Can conduct electricity- delocalised electron as only 3 carbon bonds used.
Describe the features of silica.
- Very high melting point.
- Strong
- Each silicon atom is joined to four oxygens.
- Each oxygen is bonded to 2 silicons
- Doesn’t conduct electricity.
What are resonance structures?
Sets of Lewis structures that describe the delocalisation of electrons in a polyatomic ion or molecule.
What are delocalised electrons?
Electrons in a molecule, ion or solid metal that are not associated with a single atom or one covalent bond.
What must a molecule have to be able to exhibit a resonance hybrid?
A pi bond that can move from one part of the molecule to another.
Why are oxygen and ozone dissociated by different wavelengths of light?
- The chemical bonds between the oxygen in ozone are weaker than in oxygen. As a result, less energetic photons meaning those with longer wavelengths can break apart ozone molecules.
- Oxygen molecules have stronger bonds, so they can only absorb a small range of higher energy, shorter wavelength UV light.
- Ozone have weaker bonds, so they can absorb a broader range of wavelengths, including lower energy, longer wavelength UV light.
