C3 Structure And Bonding Flashcards
Limitations of the particle model
The atoms, molecules and ions that make up all substances are not solid spheres with no forces between them
Three types of bonding
Covalent, ionic and metallic
What ions do Group 4 elements form?
They do not form ions apart from tin and lead
How does ionic bonding work?
Ionic compounds are held together by strong forces of attraction between their positively charged ions.
Why do ionic compounds have high melting and boiling points?
To seperate the ions you have to overcome all the electrostatic forces of attraction acting in all directions
When do ionic compounds conduct electricity.
When molten or dissolved in water. This is because their ions can then become mobile and can carry charge through the liquid
When are covalent bonds formed?
When atoms of non-metals share pairs of electrons with each other
Covalent structures
Many substances containing covalent bonds consist of simple molecules but some have giant covalent structures
Why do substances made up of simple molecules have low melting and boiling points?
The forces between simple molecules are weak
Why don’t substances made of simple molecules conduct electricity?
Simple molecules have no overall charge, so they cannot carry electrical charge
Limitations of 2D ball and stick models
They don’t show the true shape of the molecule. It shows the H-C-H bond angles as 90 degrees where as it is actually 109.5 degrees. A 3D model allows you to appreciate its tetrahedral shape more easily.
Limitations of models drawn on paper
Scientists believe that the electrons in covalent bonds are constantly moving, but on average are found most of the time between the two nuclei of the atoms they are bonding together
Giant covalent structures
Some covalently-bonded substances have giant structures. These susbstances have very high melting points and boiling points.
How can graphite conduct electrical and thermal energy?
Each carbon atom forms three strong covalent bonds. Carbon atoms have four electrons in their outer shells available for bonding, leaving one spare outer electron on each carbon atom in graphite. These delocalised electrons can move along its layers and allow graphite to conduct electricity.
Properties of graphite
Graphite contains giant layers of covalently bonded carbon atoms. However, there are no covalent bonds betwen the layers. This means they can slide over each other, making graphite soft and slippery.
Properties of diamond
The carbon atoms in diamond have a rigid covalent structure, making it a very hard substance
Apart from diamond and graphite, how else does carbon exist?
Carbon also exists as fullerenes, which can form large cage-like structures and tubes, based on hexagonal rings of carbon atoms
Uses of fullerenes
The fullerenes are finding uses as a transport mechanism for drugs to specific sites in the body, as catalysts, and as a reinforcement for composite materials
Properties of fullerenes
High tensile strength and high electrical conductivity (because their bonding is like the bonding in graphite, giving them delocalised electrons, resulting in their use in the electronics industry)
What is graphene?
A single layer of graphite and so is just one atom thick. Its properties, such as its excellent electrical conductivity, will help create new developments in the electronics industry in the future
Cations
Positive ions
How are atoms in metals arranged?
Closely packed together and arranged in regular layers
Metal bonding
Outer electrons from each metal atom form a ‘sea’ of delocalised electrons. Strong electrostatic forces between the negatively charged elecrons and the positively charged ions bond the metal ions to each other.
Alloy
A mixture of one or more elements, at least one of which is a metal
Why can metals be bent and shaped?
The layer of atoms (or positively charged ions) in a giant metallic structure can slide over each other.
Why are alloys harder than pure metals?
The regular layers in a pure metal are distorted by atoms of different sizes in an alloy.
Why are metals good electrical and thermal conductors?
Delocalised electrons in metals enable electricity and thermal energy to be transferred through a metal easily
1 nanonmetre (1nm) =
1x10^-9 metres
As the side of a cube decreases in size by a factor of 10…
Its surface area to volume ratio increases by 10
What is nanoscience?
The study of small particles that are between 1 and 100 nanometres in size
Properties of nanoparticles
Nanoparticles may have properties different from those for the same material in bulk. This arises because nanoparticles have a high surface area to volume ratio, with a high percentage of their atoms exposed at their surface
The use of nanoparticles instead of traditional bulk materials should mean that…
Smaller quantities are needed. Nanoparticles’ high surface area to volume ratio makes them much more reactive than materials with normal particles sizes. This will result in a more sustainable approach in industry as less resources are used up
Uses of nanoparticles
Modern sunscreens (titanium and zinc oxide nanoparticles), in cosmetic products (they can work deeper in the skin) and antimicrobial coatings (silver nanoparticles)
Uses of nanoparticles in fighting cancer
Nanocages of gold can deliver drugs where they need to go in the body. Tiny gold particles can be injected and absorbed by tumours as they have thin, leaky blood vessels with holes large enough for the nanoparticles to pass into. However, they cannot get into the healthy blood vessels. A laser is directed at the tumour and energy is transferred to the gold nanoparticles, causing them to warm up quickly. The temperature of the tumour changes the properties of its proteins but barely warms the surrounding tissue.
Possible risks of nanoparticles
If nanoparticles are used more and more, there is more of a risk of them finding their way into the environment and scientists believe that breathing in tiny particles can damage the lungs. Aquatic life could also be affected. Their large surface area makes them very effective catalysts and scientists are developing these for use in fuel cells. However, their large surface area makes them dangerous as if there is a spark near a large quantity of the catalyst, there could be a violent explosion.
