C3 Structure and bonding Flashcards
What are the three states of matter?
Solids, liquids and gases
Solids
- Fixed shape and volume
- Cannot be compressed
Liquids
- Fixed volume
- Can flow and change their shape
Gases
- No fixed shape or volume
- Can be compressed easily
Particle theory - solids
- Each particle in a solid is touching its nearest neighbour and they remain in this fixed arrangement
- They cannot move around but they do vibrate constantly
- High density
- Low energy
Particle theory - liquids
- The particles in a liquid are also very close together but they can move past each other
- This results in a constantly changing, random arrangement of particles
- Medium density
- Greater energy than in solids
Particle theory - gases
- The particles in a gas have on average, much more space between them
- They can move around at high speeds in any direction
- This means the particles have a random arrangement
- The hotter the gas, the faster the particles move
- The pressure of a gas is caused by the particles colliding with the sides of the container
- The more frequent and energetic the collisions are, the higher the pressure of the gas (in a sealed container the pressure of gas increases with temperature)
- Low density
- Highest energy
Limitations of the particle model
The atoms, molecules, and ions that make up all substances are not solid spheres with no forces operating between them
Energy transfers during change of state
- In melting and boiling, energy is transferred from the surroundings to the substance (endothermic)
- In freezing and condensing, energy is transferred from the substance to the surroundings (exothermic)
Compound
Contains two or more elements, which are chemically combined
Covalent bonding
Non-metal atoms share electrons between each other
Ionic bonding
- Metals and non-metals react by transferring electrons
- The atoms involved are oppositely charged particles (known as ions) in which electron transfer occurs
- The ions formed are held next to each other by very strong electrostatic forces of attraction between the oppositely charged ions
- The ionic bonds between the charge particles result in an arrangement of ions called a giant structure or giant lattice
Ions and the periodic table
- Group 1 form 1+ ions
- Group 2 form 2+ ions
- Group 3 form 3+ ions, when they form ions as opposed to sharing electrons
- Group 4 do not form ions (apart from tin (Sn), lead (Pb), at the bottom of the group)
- Group 5 form 3- ions, when they form ions as opposed to sharing electrons
- Group 6 form 2- ions, when they form ions as opposed to sharing electrons
- Group 7 form 1- ions, when they form ions as opposed to sharing electrons
- Group 0 never form ions in compounds
Metallic bonding
- Metal ions are arranged in regular layers, on top of each other
- Positively charged metal ions, which are held together by electrons from the outermost shell of each metal atom
- Strong electrostatic attraction between the negatively charged electrons and the positively charged ions bond the metal ions to each other
- These delocalised electrons are free to move throughout the giant metallic lattice
General properties of giant covalent structures
- Very high melting and boiling points
- Insoluble in water
- Apart from graphite, they are hard and do not conduct electricity
Bonding in graphite
- Carbon atoms are only bonded to three other carbon atoms
- Carbon atoms have four electrons in their outer shell available for bonding. This leaves one spare outer electron on each carbon atom in graphite
- They form hexagons, which are arranged in giant layers
- There are no covalent bonds between the layers, only weak intermolecular forces, so the layers can slide over each other. This makes graphite soft and slippery
- Graphite can conduct electricity and thermal energy because of the delocalised electrons that can move along its layers
What is an alloy?
A mixture of two or more elements, at least one of which is a metal
Carbon nanotubes properties
- High tensile strength, leading to their use in reinforcing composite materials, such as those used in making tennis rackets
- High electrical conductivity and high thermal conductivity, because their bonding is like the bonding in graphite, giving them delocalised electrons, resulting in their use in the electronics industry
Fullerenes
- Carbon atoms join together to make large hollow cages
- The structures are based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms
What is graphene?
A single layer of graphite
Properties of graphene
- Excellent conductor of electricity and thermal energy
- Very low density
- Very strong
Explain how a covalent bond holds two atoms together
Electrostatic force of attraction between shared pair of negatively charged electrons and the positively charged nuclei.
What shape is a Buckminsterfullerene molecule?
Spherical
What are the uses of a fullerene?
- Drug delivery around the body
- Catalysts
- Lubricants
Explain why graphite is a good electrical conductor and is soft and slippery
- Graphite contains covalent bonds and is a macromolecular structure
- There are three covalent bonds per carbon atom so one electron per carbon atom is delocalised
- These delocalised electrons can move through the structure and carry electrical charge, so graphite conducts electricity
- The layered structure of interlocking hexagonal rings has no covalent bonds between layers so the layers can slide over each other, so graphite is soft and slippery
Explain why sodium oxide has a high melting point
- It is a giant structure
- With strong electrostatic forces of attraction between ions
- So large amounts of energy are needed to break the bonds
Explain why alloys are harder than pure metals
- In an alloy the atoms are different sizes
- So the layers are distorted
- The layers slide over each other less easily
