⚠ 2. Bonding, structure, and the properties of matter Flashcards
Three types of chemical bonds
- Ionic
- Covalent
- Metallic
Where are the electrostatic forces of attraction in ionic bonds?
Strong electrostatic forces of attraction between the oppositely charged ions
Where are the electrostatic forces of attraction in covalent bonds?
Nuclei of two atoms and a shared pair of electrons
Where are the electrostatic forces of attraction in metallic bonds?
Nuclei of atoms and delocalised electrons
What is an ion?
An atom with a positive or negative charge that has gained or lost electrons to obtain a full outer shell
Explain Ionic Bonding in terms of metals and non metals
- When a metal atom reacts with a non-metal atom, electrons in the outer shell of the metal atom are transferred.
- Metal atoms lose electrons to become positively charged ions. Non-metal atoms gain electrons to become negatively charged ions.
Dot and Cross Diagram
& Limitations
Ionic Compounds & Properties
- Form Giant regular structures known as a giant ionic lattice
- Strong electrostatic forces of attraction in all directions between oppositely charged ions
- High melting & boiling points because lots of energy is needed to break down the strong bonds
- Can only conduct electricity in molten or liquid form because the ions are free to move so charge can flow
Ball and Stick Diagram
& Limitations
2D + 3D Diagrams
& Limitations
What is Covalent Bonding?
The sharing of pairs of electrons between non-metal atoms
Note: A molecule is a group of two or more atoms joined together by covalent bonds
Which type of bond are molecules?
Covalent bonds
Properties of Covalent Bonds
& small molecules
- Covalent Bonds are strong bonds
- Covalent Bonds have weak intermolecular forces
- Small molecules are usually gases or liquids that have low melting or boiling points because the weak intermolecular forces are easily overcome
- The larger the molecules are, the stronger the intermolecular forces, so the melting and boiling points increase
- They cannot conduct electricity because the molecules have no overall charge
Giant Covalent Structures & Properties
They are many atoms joined together by covalent bonds in a giant lattice structure
- High melting and boiling points as there are a large number of bonds to be broken in a giant covalent structure, and all the bonds are linked by strong covalent bonds
Examples of Giant Covalent Structures
Diamond, Graphite ( + graphene ), and silicon dioxide
Diamond & Properties
- A giant covalent structure
- Each carbon atom is bonded with 4 other carbon atoms
- Does not conduct electricity
- Rigid network held together by stong covalent bonds, so:
- It is hard enough to resist forces that could distort the structure
- It has a very high melting and boiling point
Graphite & Properties
- A giant covalent structure
- Has hexagonal rings in layers
- There are weak intermolecular forces between the layers which means that the layers can slide past each other - making graphite soft and slippery
- Each carbon atom is bonded with 3 other carbon atoms
- Carbon has 4 electrons - 3 are bonded - so there is one delocalised electron for each carbon atom in graphite
- Delocalised electrons mean that they are free to move so they can conduct electricity and heat
Graphene & Properties
A single layer of graphite so it is transparent and flexible
• Strong covalent bonds which means:
- High melting point
- Very strong - useful for making composites
• Has delocalised electrons so it conducts electricity - useful in electronics
Fullerenes
& Examples
Molecules of carbon atoms with hollow shapes ( such as tubes, balls and cages )
• Fullerenes have a structure of hexagonal rings with 5, 6 or 7 carbon atoms
Examples: Buckministerfullerene (C60), Carbon Nanotubes
Buckministerfullerene
- Consists of 60 carbon atoms
- Each atom bonded to 3 other carbon atoms
- Arranged in rings of 5-6 atoms (pentagons & hexagons)
- Weak intermolecular forces between the molecules of buckministerfullerene, so it is slippery
- Because it is slippery and spherical, it is useful for lubricants
Carbon Nanotubes
- Cylindrical fullerenes
- Very high length to diameter ratios - ( Very long compared to their width )
- This makes them useful for nanotechnology, electronics and materials (they conduct electricity)
Polymers
- Polymers have very large molecules
- They are linked to other atoms by strong covalent bonds
- The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.
What is metallic bonding?
- How are they organised?
- Talk about their attraction
Metallic bonding is the bonding of metal atoms
- It consists of a giant structure of metal atoms - which are positive ions - and a sea of delocalised electrons which are free to move through the structure
- The sharing of delocalised electrons results in strong metallic bonds.
Properties of metals
- High melting and boiling points as lots of energy required to break a number of strong metallic bonds
- Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal.
- Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons.
- Particles in pure metals have a regular arrangement and size, so the layers are able to slide over each other, resulting in them being malleable (bent) and ductile (pulled/shaped)
Alloys
- What is it?
- Why is it used?
- An example
- An alloy is a mixture of two or more elements
- Pure metals are too soft for many uses due to their regular arrangement and size
- They are mixed with other metals to make alloys, which are harder because the different-sized atoms distort the layers to slide over each other
- Steel is an alloy made of iron and small amounts of carbon
Nanoscience & Nanoparticles
- Nanoscience is the study of structures that are between 1 and 100 nanometres (nm) in size.
- Nanoparticles are only a few hundred atoms in size
- They have a high surface area to volume ratio
Nanoparticle Uses
Advantages & Disadvantages
- Electronics - They have high length to diameter ratio
- Sun Creams - They are small in size so are invisible to skin. However, it is difficult to see where it has been applied as it is invisible to skin
- Deodorants - High surface area to volume ratio
- Catalysts - High surface area to volume ratio
Where does ionic bonding occur?
Occurs in compounds formed of metals combining with non-metals
Where does covalent bonding occur?
Occurs in compounds of non metals
Where does metallic bonding occur?
Occurs in metallic elements and alloys
