C3: Structure & Bonding Flashcards
What is ionic bonding?
When a metal and a non-metal react together, the metal atom loses electrons to form a positively charged ion and the non-metal gains these electrons to form a negatively charged ion. These oppositely charged ions are strongly attracted to one another by electrostatic forces. This attraction is called ionic bonding.
What is an ionic compound?
They have a structure called a giant ionic lattice.
Ions form a closely packed regular lattice arrangement and there are very strong electrostatic forces of attraction between oppositely charged ions, in all direction in the lattice
Ionic compound properties?
They have high melting and boiling points due to many strong bonds between the ions.
When they are solid, they can’t conduct electricity, when they melt, the ions are free to move and they’ll carry electric charge.
Some dissolve in water and carry electric charge.
What is a covalent bond?
When non-metal atoms bond together, they share pairs of electrons to make covalent bonds.
Features of simple molecular substances?
Very strong covalent bonds
Weak intermolecular forces
Melting points very low, because the molecules are easily parted from each other
Most are gases or liquids at room temperature
As molecules get bigger, the strength of the intermolecular forces increases, so more energy is needed to break them and the melting and boiling points increase
Molecular compounds don’t conduct electricity, because they aren’t charged so there are no free electrons or ions
Characteristics of polymers?
All the atoms in a polymer are joined by strong covalent bonds
The intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is needed to break them.
Most polymers are solid at room temperature.
The intermolecular forces are still weaker than ionic or covalent bonds, so they generally have lower boiling points than ionic or giant molecular compounds.
Characteristics of giant covalent structures?
All the atoms are bonded to each other by strong covalent bonds
They have very high melting and boiling points
They don’t contain charged particles, so they don’t conduct electricity
The main examples are diamond, graphite (which are both made from carbon atoms only) and silicon dioxide.
What are allotropes?
Different structural forms of the same element in the same physical state.
Features of diamond?
Giant covalent structure, made up of carbon atoms that each form four covalent bonds.
This makes diamond really hard
Very high melting point
Doesn’t conduct electricity because it has no free electrons of ions.
Features of graphite?
In graphite, each carbon atom only forms three covalent bonds, creating sheets of carbon atoms arranged in hexagons.
There aren’t any covalent bonds between the layers - they are held together weakly, so they’re free to move over each other. This makes graphite soft and slippery, so it’s ideal as a lubricating material.
High melting point, the covalent bonds in the layers need loads of energy to break.
Only three out of each carbons four outer electrons are used in bonds so each carbon atom has one electron that’s delocalised. So graphite conducts electricity and thermal energy.
Features of graphene?
A sheet of carbon atoms joined together in hexagons.
One atom thick, two dimensional substance.
The network of covalent bonds makes it very strong.
Very light
Like graphite, it contains delocalised electrons so can conduct electricity through the whole structure.
Features of fullerenes?
Fullerenes are molecules of carbon shaped like closed tubes or hollow balls
They’re mainly made up of carbon atoms arranged in hexagons, but can also contain pentagons or heptagons (seven).
The fullerene structure forms around another atom or molecule, which is then trapped inside. This could be used to deliver a drug into the body.
They have a huge surface area, so they could help make great industrial catalysts, individual catalyst molecules could be attached to the fullerenes.
They also make great lubricants.
Features of nanotubes?
Ration between the length and the diameter of nanotubes is very high.
Conduct both electricity and heat.
High tensile strength (they don’t break when stretched).
Nanotubes can be used in electronics or to strengthen materials without adding much weight such as tennis racket frames.
What is metallic bonding?
Metals consist of a giant structure.
The electrons in the outer shell of the metal atoms are delocalised. There are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons.
These forces of attraction hold the atoms together in a regular structure and are known as metallic bonding.
It is very strong.
Features of metallic bonding?
Substance that are held together by metallic bonding include metallic elements and alloys.
High melting points and boiling points (generally solid at room temperature), strong electrostatic forces between the metal atoms and the delocalised sea of electrons.
The delocalised electrons carry electric charging and thermal heat energy throughout the whole structure.
The layers of atoms in a metal can slide over each other making metals malleable. This means they can be bent or hammered or rolled into flat sheets.
What is an alloy and what makes it hard?
A mixture of two or more metals or a metal and another element.
Different elements have different sized atoms, so when another element is mixed with a pure metal, the new metal atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other. This makes alloys harder than pure metals.
How do you work out the surface area to volume ratio?
SA/V
What does the large surface area to volume ration mean?
Properties of nanoparticle material may be different to those of the same materials in bulk. For example, you’ll often need less of a material that’s made up of nano particles to work as an effective catalyst compared to a material made up of normal sized particles (containing billions of atoms rather than a few hundred).
What size are the particles studied in nanoscience?
1nm-10nm diameter
Uses of nanoparticles?
Nanomedicine. The idea that tiny particles such as fluorine are absorbed more easily by the body than most particles. This means that deliver drugs right into the cell where they needed.
Some nanoparticles conduct electricity so they can be used and tiny electrical circuits for computer chips.
Silver nanoparticles have antibacterial properties. They can be added to polymer fibres that are then used to make surgical masks and wound dressings and they can also be added to deodorants.
Nano particles are also being used in cosmetics, for example they used to improve moisturisers without making them oily.
Disadvantages of nanoparticles?
Products containing nanoparticles have been made available before the effects on human health have been investigated properly, and that we don’t know the long-term impacts on health.
Many people believe that products containing nanoscale particles should be clearly labelled so that consumers can choose whether or not to use them.
Example of a bad nanoparticle?
They are being used in suncreams as they have been shown to be better than the materials in traditional sun creams at protecting skin from harmful UV rays.
They also give better skin coverage than traditional suncreams.
But yet it’s not clear whether the particles can get into your body and if they do whether they might damage cells.
It’s also possible that when they are washed away, they might damage the environment .
