Bonding Flashcards
What is ionic bonding?
Ionic bonding is the electrostatic attraction between positive and negative
ions.
It is a relatively strong attraction.
How are ionic compounds held together?
● They are held together in a giant lattice.
● It’s a regular structure that extends in all directions in a
substance.
● Electrostatic attraction between positive and negative ions holds
the structure together.
State properties of ionic substances
● High melting and boiling point (strong electrostatic forces between
oppositely charged ions)
● Do not conduct electricity when solid (ions in fixed positions).
● Conduct when molten or dissolved in water - ions are free to move.
What is a covalent bond?
Covalent bond is a shared pair of electrons between two atoms.
Describe the structure and properties of simple
molecular covalent substances
- Do not conduct electricity (no ions)
- Small molecules
- Weak intermolecular forces, therefore:
- Low melting and boiling points
How do intermolecular forces change as the
mass/size of the molecule increases?
They increase. That causes melting/boiling points to increase as well (more
energy needed to overcome these forces).
What are polymers?
Polymers are very large molecules (>100s, 1000s of atoms) with atoms linked by
covalent bonds.
What are giant covalent substances? Give examples
- Solids, atoms covalently bonded together in a giant lattice.
- High melting/boiling points – strong covalent bonds.
- Mostly don’t conduct electricity (no delocalised e−
) - Diamond, graphite, silicon dioxide.
Describe and explain the
properties of allotropes of carbon.
Diamond
– four, strong covalent bonds for each carbon atom
– very hard (Strong bonds)
– very high melting point (strong bonds)
– does not conduct (no delocalised electrons)
Graphite
– three covalent bonds for each carbon atom
– layers of hexagonal rings
– high melting point
– layers free to slide as weak intermolecular forces
between layers; soft, can be used as a lubricant
– conduct thermal and electricity due to one delocalised
electron per each carbon atom
Fullerenes
– hollow shaped molecules
– based on hexagonal rings but may have
5/7-carbon rings
– C60 has spherical shape, simple
molecular structure (Buckminsterfullerene)
Nanotubes
– cylindrical fullerene with high length to
diameter ratio
- High tensile strength (strong bonds)
- Conductivity (deloc. electrons)
Graphene - a single layer of graphite.
What is metallic bonding?
Forces of attraction between delocalised electrons and nuclei of metal
ions.
Describe properties of metals
- High melting/boiling points (strong forces of attraction)
- Good conductors of heat and electricity (delocalised electrons)
- Malleable, soft (layers of atoms can slide over each other whilst maintaining
the attraction forces)
What are alloys? Why are they harder than pure
metals?
Alloys:
- mixtures of metal with other elements, usually metals
- different sizes of atoms distorts the layers, so they can’t slide over each other,
therefore alloys are harder than pure metals
What are the limitations of the simple model?
There are no forces between spheres and atoms, molecules and ions are solid
spheres – this is not true
What does the amount of energy needed to
change state from solid to liquid or liquid to gas
depend on?
The strength of the forces between the particles of the substance. The
nature of the particles involved depends on the type of bonding and the
structure of the substance. The stronger the forces between the particles
the higher the melting point and boiling point of the substance
State the uses of
nanoparticles
- Medicine (drug delivery systems)
- Electronics
- Deodorants
- Sun creams (better skin coverage and more effective protection
against cell damage)
