C3: Structure And Bonding Flashcards
What is happening with temperature and energy describe the movement of particles at the melting point of a substance?
When a solid is heated to its melting point, the kinetic energy of the particles tends to increase and their movement also starts increasing. The bond present between the particles starts breaking and these particles start vibrating at their own position.
What factors effect rate of evaporation?
Temperature: When the temperature is high, the kinetic energy of the water particles increases, leading to the quicker conversion of liquid water into its gaseous state.
- Surface area: A larger surface area gives more space for the water particles to evaporate and further allow more direct heat on the surface
- Humidity: Evaporation occurs more slowly in high humidity because there is already a lot of water vapor in the surrounding air.
how is attraction between particles affected when a substance is heated
As a substance is heated, particles gain more kinetic energy causing them to move and vibrate. These small movement competes with the attraction between particles and causes them to move slightly further apart. The bind between particles gradually weakens and is eventually broken.
How are ions formed?
An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons. This loss or gain of electrons takes place to obtain a full outer shell of electrons
What are negatively and positively charged ions called?
Anion, Cations
What do metals form when losing electrons?
Cations
What do non-metals for, when gaining electrons?
Anions
What is an ionic bond?
The electrostatic attraction between the opposite charges of negatively charged non-metal cations and positively charged metal anions.
What charge does an ionic compound have?
Neutral as the opposite charges are balanced
How are ionic bonds represented in a diagram?
Ionic bonds can be representeddiagrammatically using dot and cross diagrams. The electrons from each atom should be represented by using solid dots and crosses. If there are more than two atoms, then hollow circles or other symbols / colours may be used to make it clear
The large square brackets should encompass each atom and the charge should be in
superscript and on the right-hand side, outside the brackets. For larger atoms with more electron shells, only the valenceshell needs to be drawn
What is a monatomic ion?
A charged particle that consist of only one atom
What are the properties of monatomics?
Individual atoms with very weak forces between them. They have no bonds. Lowest melting and boiling points; weak bonds. Monatomic elements can’t conduct electricity. Not soluble
What are the properties of simple molecular structures?
Lots of individual molecules with weak forces between the molecules. Covalent bonding. Quite low melting and boiling points. This is because the weal intermolecular forces are easy to overcome, requiring little heat energy. Cannot conduct electricity even when in solution in liquid form. Insoluble in water and other solvents
What are the properties of giant covalent structures?
Lattice structure in which all atoms are joined together in a giant network by covalent bonds. High melting and boiling points as they have stri attractions and require lots of energy to overcome. Most cannot conduct electricity as they have no charged particles that are free to move. Cannot form strong attractions with water, therefore insoluble
What are the properties of giant ionic lattice structures?
Lattice structure of positive and negative ions, held together by the electrostatic attraction of oppositely charged ions. High melting and boiling points because they are strongly attracted and hard to overcome. Insulators when solid and conductors of electricity when molten or in solution. Most are soluble, both ionic and water molecules are charged
What are the properties of metallic structures?
Lattice structure of metal atoms where the outer shell electrons from each atom are delocalised (i.e. these electrons are free to move through the structure). There is a strong attraction between the positive nucleus of the atoms and the cloud of negative delocalised electrons (this is known as metallic bonding). Ussually very high meltung and boiling points as a lot of heat energy is needed to overcome the strong attraction. High electrical conductivity as electrons are free-flowing. Insoluble in water
What is a giant lattice structure
Giant ionic lattices are regular structures, held together by ionic bonds. These ionic bonds are strong electrostatic forces of attraction between oppositely charged ions, acting in all directions and arranged in an alternating pattern
What is an allotrope?
Different forms of the same element
What is an isotope?
Same element with the same number of protons but different numbers of neutrons and therefore, different atomic masses/ mass numbers
Why do ionic compounds have a high melting point?
The ionic compounds are made up of positive and negative ions which have the strong force of attraction between opposite charged ions. So, a lot of heat energy is required to break this force of attraction or ionic bond due to this ionic compounds have high melting points.
Why can ionic compound not conduct electricity when solid but can when molten or in a solution?
This is because both processes make their ions free to move from place to place. Ionic compounds cannot conduct electricity when solid, as their ions are held in fixed positions and cannot move. Ionic compounds are conductors of electricity when molten or in solution and insulators when solid.
What is a covalent bond?
Non-metal atoms can share electrons with other non-metal atoms to obtain a full outer shell of electrons. When two atoms share pairs of electrons, they form covalent bonds
What are the limitations of the ball and stick model?
The 3D ball and stick model shows the arrangement of oppositely charged ions but
represents ionic bonds as sticks between ions; in reality an ionic bond is an electrostatic
force of attraction that acts in all directions around an ion
Another limitation of the 3D ball and stick model is that it incorrectly depicts space existing
between individual ions whereas the 3D space-filling model is more accurate (there is not
much space between separate ions)
It is di cult to represent the relative sizes of the ions in relation to each other correctly in
any model
How are molecules formed?
When two or more atoms are covalently bonded together.
What are non bonding electrons
Electrons on the outer shell which are not involved in the covalent bond
Why do simple covalent molecules not conduct electricity?
As they do not contain free electrons
How is a single covalent bond represented?
A shared pair of electrons or a singular line
How many covalent bonds does O2 have?
2
How many covalent bonds does a molecule of N2 have?
Three
How are the properties of a molecule with double covalent bond different to a molecule with a singular covalent bond?
The bond is stringer and shorter than a singular bond, making it more difficult to overcome the bond.
how does the size of molecules affect melting and boiling points?
Larger molecules have stronger intermolecular forces as the molecules increase in size the intermolecular forces also increase as there are more electrons available, thus requiring more thermal energy to overcome the forces. Subsequently, larger molecules have higher melting and boiling points.
Why do small molecules have low melting and boiling points?
Because little thermal energy is required to overcome the weak intermolecular forces between molecules whilst the covalent bonds are much more difficult to overcome.
Why do small molecules not conduct electricity?
Because all electrons have a fixed position. The molecules therefore have no free flowing electrons to carry the electronic charge.
What are intermolecular forces?
Intermolecular forces are the forces of attraction or repulsion that exist between molecules in a substance. These forces arise due to the interactions between the electrically charged particles (electrons and nuclei) that make up the molecules.
What are four allotropes of carbon?
Diamond
Graphite
Graphene
Buckminsterfullerene
What types of structure is diamond?
Giant covalent
What types of structure is graphite?
Giant covalent
What types of structure type is buckminsterfullerene?
Simple molecular
What type of structure is graphene?
What is the melting and boiling point of diamond?
Very high as lots of energy is required to break strong covalent bonds
What is the melting and boiling point of graphite?
Very high as lots of energy is required to break strong covalent bonds
What is the melting and boiling point of buckminsterfullerene?
Quite low as little energy is needed to overcome relatively weak intermolecular forces (no covalent bonds brokem)
What is the electrical conductivity of diamond?
Insulator as it has no delocalised electrons
What is the electrical conductivity of graphite?
Conductor as it has delocalised electrons that can carry charge between layers of graphene
What is the electrical conductivity of buckminsterfullerene?
Insulator as it has delocalised electrons but they cannot move from one molecule to another and thus cannot carry an electrical charge
What is the electrical conductivity of graphene?
Conductor as it has delocalised electrons that can carry charge through the structure
What is the strength of diamond?
Very strong as the strong covalent bonds between carbon atoms in diamond create a tightly packed and uniform structure, making it difficult for atoms to slide past each other
What is the strength of graphite?
Soft and brittle because the layers of graphene are weakly bonded together, they slide over each other easily.
What is the strength of buckminsterfullerene?
Soft and brittle as little force is required to break the weak intermolecular forces
What is the strength of graphene?
Very hard and strong due to the many, strong covalent bonds between the carbon atoms. These covalent bonds are difficult to overcome and require a lot of energy
What is the formula for diamond, graphite, buckminsterfullerene and graphene?
C, C, C60, C
what is a use of diamond due to its properties?
Diamond has the highest hardness and thermal conductivity of any natural material, properties that are used in major industrial applications such as cutting and polishing tools.
What is a use of graphite due to its properties?
- Owing to graphite’s soft and slippery nature, it is used as a grease, a type of lubricant.
- Due to its high electrical conductivity, graphite is reflected in the making of electrodes for electric furnaces.
- The high melting point of graphite makes it suitable for making crucibles for melting metals.
What is a use of graphene due to its properties
Graphene makes composite materials stronger without making them much heavier so is often used in electronics and construction (eg: solar panels and batteries)
What is the structure of a fullerene?
Fullerenes are molecules of carbon atoms with hollow shapes. Their structures are based on hexagonal rings of carbon atoms joined by covalent bonds.
What is the structure of nanotubes?
Nanotubes are a type of fullerene and are molecular-scale tubes of carbon arranged similarly to the layers in graphite. Carbon nanotubes have a very high melting point, as each carbon atom is joined to three other carbon atoms by strong covalent bonds.
What is the use of nanotubes
Like graphene, nanotubes are strong and conduct electricity because they have delocalised electrons. These properties make nanotubes useful for nanotechnology, electronics and specialised materials.
What is the use of fullerenes?
Fullerenes can be used to trap other molecules by forming around the target molecule and capturing it, making them useful for targeted drug delivery systems. They also have a huge surface area and are useful for trapping catalyst molecules onto their surfaces making them easily accessible to reactants so catalysis can take place. For instance fullerenes can be used to deliver medication around the body as it can be absorbed more easily by the body. Fullerene can also bond to transition metals, which is useful in the catalysis of reactions.
Name 3 ways in which ionic bonds are different to covalent bonds
Only non-metals are present, electrons are shared not transfered, particles are together by the attraction of the nuclei and electrons rather than oppositely charged ions.
What are delocalised electrons?
Delocalised electrons are electrons that are free-flowing and are not associated with a particular
atom or covalent bond
What is a metallic bond?
Metallic bonds are the chemical bonds between positively charged cations, sharing delocalised electrons amongst a giant lattice structure.
What holds metal atoms together in a metallic bond?
The electrostatic attractive force between conduction electrons and positively charged metal ions
What is a crystalline structure?
A large number of atoms covalently bonded together in a 3-dimensional arrangement forming a cystalline structure
Describe the giant covalent structure of graphite
Carbon atoms each have 3 covalent bonds with surrounding carbon atoms. The 4th bond is made with delocalised electrons between layers of graphite.
What is an alloy?
An alloy is a mixture of two or more elements, at least one of which is a metal
What are the advantages of the ball and stick diagram?
Useful for illustrating the arrangement of atoms in 3D space
Especially useful for visualizing the shape of a molecule
What are the disadvantages of the ball and stick diagram?
Fails at indicating the movement of electrons
The atoms are placed far apart from each other, which in reality is not the case as the gaps between atoms are much smaller
What are the advantages of dot and cross diagrams?
Useful for illustrating the transfer of electrons
Indicates from which atom the bonding electrons come from
What are the disadvantages of the dot and cross diagram?
Fails to illustrate the 3D arrangements of the atoms and electron shells
Doesn’t indicate the relative sizes of the atoms
Why do metal atoms become cations in a metal lattice?
Within the metal lattice, the atoms lose their valence electrons and become positively charged metal ions
What is a use of small molecules?
Insulators as they cannot conduct electricity in a solid state
What are properties of metals?
- Maluable
- Reflective
- Ductile (Easily stretched without breaking or lowering in material strength)
- High melting points
- Conductors
Why are metals malleable?
The layers of atoms in metals can slide over each other but are still held together by the delocalised electrons, preventing them from being brittle, meaning metals are malleable and can be hammered and bent into shapes or rolled into flat sheets
Why are metals conductors?
Because giant metallic lattice structures have delocalised electrons, which can carry an electrical charge through the material
Why do metals have a high melting/ boiling point?
Due to the strong electrostatic attraction due to the opposite charges of the nuclei and delocalised electrons, lots of energy is required to break this force.
Why are metals ductile?
Most metals are both ductile and malleable. This is because the structure of most metals — repeating atoms layered on top of each other — allows for relatively easy movement between them. These layers tend to slip or roll over each other.
What are the effects of alloying in materials?
In addition to increasing the strength of a metal, alloying may change other properties, including the resistance to heat, corrosion resistance, magnetic properties, or electrical conductivity.
Why does alloying increase a material’s strength?
Alloying interrupts the regular repeating pattern within a giant metallic lattice through adding atoms of alternate sizes.This increases difficulty for layers to slide over each other when an external force is applied, therefore increasing the strength of materials.
What is the is the size of ‘nano’?
1 x 10^-9 metres
How large are nanoparticles?
1nm-100nm in diameter
What is the diameter of fine particles?
1x10^-7 m to 2.5x10^-6 m
Or
1000nm - 2500nm
What is the diameter of course particles (dust)?
2.5x10^-6 m to 1x10^-5 m
Or
2500nm-10000nm
What are the soluble salts / compounds?
SLAPN Salts:
Sodium
Lithium
Ammonium
Potassium
Nitrate
What is nanoscience?
The research of nanoparticles
Why do nanoparticles have such a high surface area: volume ratio?
As particles decrease in size, their surface area increases in relation to their volume
Eg: As the side of a cube decreases by a factor of 10, the surface area to volume ratio increases
by a factor of 10
Why is surface area: volume ratio important for catalysts?
The higher the ratio then the more surface area is available for reaction, hence the better the catalyst
What are uses of nanoparticles?
- Sun cream
- Drug delivery
- Catalysts
- Cosmetic creams
- Deodorants- absorb odour
- Cleaning purposes
What are silver nanoparticles used for?
Cleaning surgical equipment, anti-bacterial coatings to prevent odours, spirt clothing to prevent body odour
What is the use of titanium dioxide nanoparticles?
Titanium dioxide in nanoparticle form is used in sunscreens as it blocks UV light but leaves no white marks on the skin while also providing better coverage than other suncreams- smaller particles absorb more UV due to a higher surface area, needing less suncream
The same chemical in bulk form is used as a white pigment in paints
Self-cleaning windows
What is the use of fullerenes (nano) ?
Fullerenes are used in medicine and drug design as they are more easily absorbed than other particles and can deliver drugs to target areas more e ffectively
Fullerenes are also used in electronic circuitry and as coatings for artificial limbs and joints
What are the advantages of nanotechnology?
Nanoparticles have widespread uses and applications that can provide an immense advance in materials technology
What are the issues with nanotechnology?
- The use of nanoparticles in science is in its early stages so there are still a lot of unknown
factors and potential risks, in particular there is a lack of understanding on how they may effect health - Although there haven’t been any serious short term side e ects, there could be long term
side e ects which we haven’t detected yet as they haven’t been in use long enough - Even a small amount of toxicity in a particular nanoparticle would be multiplied due to the
high surface area to volume ratio - This coupled with the fact that they are not easily disposed of by the body are a cause for
caution in the medical application of nanoparticles
