C2 - Structure And Bonding Flashcards
Where does ionic bonding occur?
Ionic bonding occurs in compounds formed from metals combined with non-metals
What do metals form when they lose a valence electron?
1+ ion
What do non-metals form when they gain a valence electron?
1- ion
Describe the structure of ionic compounds
Ionic compounds have regular structures (giant ionic lattices), held together by strong electrostatic forces of attraction in all directions between oppositely charged ions
Explain why ionic substances have very high melting and boiling points
A high yield of energy is required to overcome the many strong bonds/electrostatic forces of attraction
Explain why ionic substances can conduct electricity when molten or dissolved in solution
The ions are free to move and so charge can flow
Explain why ionic substances CANNOT conduct electricity when solid
The ions are not free to move; they are fixed in place by the strong electrostatic forces of attraction
Explain why ionic substances form hard, crystalline structures
They have a regular, repeating pattern of oppositely charged ions (cations and anions) held together by electrostatic forces of attraction
A lot of energy is required to overcome the ionic bond
What do metals consist of?
Describe the structure of a metal (3)
Metals consist of giant structures of atoms arranged in a regular pattern (lattice)
-Giant lattice
- Of positive ions
- With sea of delocalised electrons
What is metallic bonding?
The strong electrostatic attraction between the positive ions and the sea of delocalised negatively charged electrons in the lattice
What does the sharing of delocalised electrons give rise to?
Strong metallic bonds
Explain why most metals have high melting and boiling points
A high yield of energy is required to overcome the strong metallic bond/electrostatic attraction
How are atoms arranged in pure metals?
Layers
Explain why metals can be bent and shaped
- Layers of particles
- Can slide past each other
Explain how pure metals are made harder
Mixed with other metals to make alloys which are harder
Explain why alloys are harder than pure metals
The different sizes of atoms distorts the layers in the pure metal. This means a greater force is required for the layers to Slide Over each other
What are alloys?
An alloy is a mixture of chemical elements of which at least one is a metal
Give three uses of alloys
- Construction
- Braces for teeth
- Shape memory alloys are useful in spectacles
Explain why metals are good conductors of electricity
The delocalised electrons in the metal carry electrical charge through the metal
Explain why metals are good conductors of thermal energy
Thermal energy is transferred by the delocalised electrons
Give two properties of small covalent molecules
- Low melting and boiling points
- Do not conduct electricity
Explain why small covalent molecules have low melting and boiling points
There is weak intermolecular forces between the molecules. This means a low yield of energy is required to overcome these forces. They usually therefore are gas or liquid at room temperature
Note: the covalent bonds are not overcome, only the intermolecular forces
As small covalent molecules become larger (Mr increases), why does their boiling point increase?
Intermolecular forces between the molecules require more energy to overcome
Explain why small covalent molecules do not conduct electricity
They do not have an overall charge
The charge on the ions produced by metals in Group 1 & 2 and by non-metals in group 6 & 7 relates to the _______ ________ of the element in the periodic table
Group number
Describe the properties of diamond in terms of its structure and bonding (rewrite this)
- Each carbon atom forms four covalent bonds with other carbon atoms in a giant structure
- Hard
- High melting point
- Does not conduct electricity
Describe the properties of graphite in terms of its structure and bonding (6)
-> why it is soft and slippery and conductor of electricity
- Each carbon atom forms 3 covalent bonds
- With one delocalised electron
- Forming layered structure of interlocking hexagonal rings with weak intermolecular forces between them
- No covalent bonds between layers so they can slide past each other so it is soft and slippery
- Delocalised electron moves throughout the structure and carries charge
Describe the properties of silicon dioxide (silica) - an example of a giant covalent structure
High melting and boiling point. This means that a huge number of strong covalent bonds must be broken, which uses a high yield of energy
Do not conduct electricity
How is graphite similar to metals?
Both are good conductors of heat and electricity. This is because both have free delocalised electrons that carry charge throughout structure
What is graphene?
Graphene is a single layer of graphite and has properties that make it useful in electronics and composites
Describe the properties of graphene in terms of its structure and bonding
- Good conductor of electricity -> delocalised electrons
- Strong covalent bonds between the carbon atoms, meaning it is strong with a high melting point
- One atom thick
What are fullerenes?
Fullerenes are molecules of carbon with hollow shapes
What was the first fullerene to be discovered? What was its shape?
Buckminsterfullerene (C60). It has a spherical shape
Give three uses of fullerenes
- Pharmaceutical delivery
- Lubricants
- Catalysts
Describe the structure of fullerenes
Based on hexagonal rings of carbon atoms, but they may also contain rings with 5 or 7 carbon atoms
What are carbon nanotubes?
Cylindrical fullerenes with very high length to diameter ratios
Describe two properties of carbon nanotubes
High tensile strength. They can be stretched without breaking
Good conductors of heat and electricity
State three uses of carbon nanotubes
- To reinforce/strengthen materials
- Nanotechnology
- Electronics
What are the allotropes of carbon?
- Fullerenes
- Diamond
- Graphite
- Nanotubes
- Graphene
What are the particles involved in all three types of strong chemical bond?
In Ionic bonding, particles are OPPOSITELY CHARGED IONS
In Covalent bonding, particles are ATOMS WHICH SHARE PAIRS OF ELECTRONS
In Metallic bonding, particles are ATOMS WHICH SHARE DELOCALISED ELECTRONS
Where does covalent bonding occur?
Covalent bonding occurs in most non-metallic elements and in compounds of non-metals
Where does metallic bonding occur?
Metallic bonding occurs in metallic elements and alloys
What are the limitations of the particle theory?
- In the model there are no forces
- Particles are represented as spheres
- The spheres are solid and inelastic
What is nanoscience?
Refers to structures that are 1-100nm in size, of the order of a few hundred atoms
What is the diameter of fine particles? (PM2.5)
What is this in standard form?
Between 100 and 2500nm
1x10^-7m and 2.5x10^-6m
What is the diameter of coarse particles/dust? (PM10)
What is this in standard form?
Diameter between 10,000nm and 2,500nm
Between 1x10^-5m and 2.5x10^-6m
Nanoparticles have very large ________ to _________ ______
Surface area to volume ratios
Nanoparticles may have properties ______ from those of the same materials in bulk because of their high ______ _______ to ________ _________. It may also mean that smaller quantities are needed to be _____ than for materials with normal particle sizes. They are more ____ than materials with normal particle sizes
Different
Surface area to volume ratio
Effective
Reactive
State six applications of Nanoparticles (Think: MECoSDC)
Medicine
In Electronics
In cosmetics
In suncreams
In deodorants
As catalysts
When a metal atom reacts with a non-metal atom in ionic bonding, what happens to the electrons?
Electrons in the outer shell of the metal atom are transferred
Suggest how Nanoparticles can be used in destroying tumour cells and for anti microbial coatings
Medicine -> tiny particles such as fullerenes are absorbed more easily by the body than most particles. This means they could deliver drugs directly to chosen cells as they can pass into leaky blood vessels with holes and destroy tumour cells without harming healthy cells.
Silver Nanoparticles have antibacterial properties and so can be added to polymer fibres. These continually release a low level of silver ions to protect against bacteria by inhibiting their growth
Suggest how Nanoparticles pose potential risks when used
- Could enter the body and damage cells by breathing in or absorption
- Could damage the environment
- Long-them effects on health unknown
Describe what happens when two atoms of potassium react with one atom of sulphur (5)
- (2) Electrons transferred from potassium to sulfur
- Two potassium atoms each lose an electron
- This forms a K+ ion
- Sulfur atom gains two electrons
- This forms S2- ion
Describe what happens when a lithium atom reacts with a chlorine atom. Answer in terms of electrons (4)
- 1 electron transferred from lithium to chlorine
- Lithium atom loses one electron
- Chlorine atom gains one electron
- This forms a Li+ ion and a Cl- ion
What are two properties of ionic substances?
- High melting point
- Dissolve in water
What are three properties of ionic compounds?
High melting point
Conduct electricity only when molten or dissolved
Does not conduct electricity when solid
Explain why sodium chloride is solid at room temperature (6)
- Strong ionic bonds
- In all directions
- Between oppositely charged ions (cations and anions)
- Forming a giant ionic lattice
- A lot of energy required to overcome these bonds
- (Giving a high MP)
What are the advantages and disadvantages of using 3D ball and stick model to represent an ionic compound?
Adv:
- Shows 3D arrangement of ions
- Shows ions and bonds
- Shows relative size of ions
- Suggests structure is extended
Disadv:
- Shows gaps between ions
- Sizes of ions are inaccurate
- Distance between ions is inaccurate
- Only outer layer of compound can be seen
What are the advantages and disadvantages of using dot and cross diagrams?
Adv:
- Shows charge of ions
- Shows where the electrons from
- Empirical formula can be derived
- Shows arrangement of electrons
Disadv:
- Does not show the structure of the compound
- Inaccurately represents sizes of ions
Describe how oxygen atoms in a carbon dioxide molecule are bonded to a carbon atom (3)
-> covalent bonding
- Two electrons from each oxygen and two from carbon form two shared pairs (double bond)
- They are attracted to the positive charge of the nuclei of the carbon and oxygen atom
- By electrostatic attraction
What are the advantages and disadvantages of representing covalent molecules using a displayed formula?
What are the advantages and disadvantages of representing covalent molecules using a dot and cross diagram?
Suggest why the boiling points increase as the number of electrons increases (3)
- More electrons as molecule becomes larger
- So greater intermolecular force
- More energy required to overcome forces
Explain why iodine has a low melting point
- Made up of small molecules
- With weak intermolecular forces
- Require little energy to overcome
What are three giant covalent structures?
Diamond
Graphite
Silicon dioxide
Describe the structure of silicon dioxide and explain why it is suitable for lining furnaces (6)
- Giant covalent structure, where each oxygen atom is bonded to TWO silicon atoms and each silicon atom is bonded to FOUR oxygen atoms
- Tetrahedral arrangement
Suitable because:
- Giant lattice/covalent structure
- With high melting point due to strong covalent bonds
- between silicon and oxygen atoms
- This requires a lot of energy to overcome
Suggest two reasons why 9 carat gold is often used instead of pure gold to make jewellery (2)
- Pure gold is too soft
- Pure gold is too expensive
- Can change the colour
Explain how corrosion affects the electrical conductivity of metals (3)
- Decreases
- As ionic compound is formed
- Which cannot conduct electricity when solid
Explain why diamond is hard
Giant covalent structure with strong covalent bonds
Explain why graphite is a lubricant
Weak intermolecular forces between molecules
So layers can slide past each other
State five properties of graphite (5)
Conducts electricity
Soft
Slippery
Brittle
High MP
Explain why graphene is strong
- Giant covalent structure
- Contains strong covalent bonds
- Lots of energy required to break them
Suggest why Buckminsterfullerene is a good lubricant
Molecules are spherical so will roll
Explain why Buckminsterfullerene could be used in medicine to deliver drugs /radioactive atoms directly to specific cells (4)
- It is a hollow sphere
- Which can cage/contain the drug molecules / radioactive atoms inside
- It has a small diameter
- So can pass through cell membranes easily
- To target only cancerous cells
Suggest why carbon nanotubes are used as lubricants
Suggest why carbon nanotubes can conduct electricity
Nanotubes can slide over each other
There is no covalent bonds between the molecules
Contain one delocalised electron
Which can move throughout the structure and carry charge
Explain why carbon nanotubes are used in catalyst systems
High surface area to volume ratio
This means that many catalyst molecules can be attached to the surface of the nanotubes
Providing a large surface area on which reactants can collide
Give three properties of carbon nanotubes
High length to diameter ratio
High tensile strength
Conducts heat and electricity
Nanoparticles of cobalt oxide can be used as catalysts in the production of hydrogen from water.
How does the size of a nanoparticle compare with the size of an atom? (1)
Suggest one reason why 1 g of cobalt oxide nano particles is a better catalyst than 1 g of cobalt oxide powder (1)
- Nanoparticles are larger of the order of a few hundred atoms
- Nanoparticles have larger surface area. This means that when attached to catalyst, there is a huge surface area to volume ratio. As a result, more collisions and faster rate of reaction
Explain why Nanoparticles are used instead of larger particles in sunscreens
- Larger surface area to volume ratio
- Smaller size makes them invisible to naked eye
- So sunscreen appears transparent on skin
Give one advantage and disadvantage of using Nanoparticles in sun screams
Better skin coverage due to high SA:V ratio
More protection from sun’s UV rays
Potential cell harm to body + harmful effects on environment
Solid = temp < MP
Gas = temp > BP
Liquid = MP < temp < BP
What is this used for?
Predicting the state of a substance
Why does PURE water not conduct electricity ?
NO IONS/delocalised electrons
What is the empirical formula?
Smallest ratio of atoms of each element in a compound (in diagram usually)
Suggest one reason why it costs less to use nanoparticles rather than fine particles in sun creams
Smaller quantity of Nanoparticles required for the same effect
-> only say this when cost/economy/more of substance is needed is involved
As the side of cube decreases by a factor of 10 the surface area to volume ratio increases by a factor of ?
10
Converse: If the side of the cube increases by a factor, the SA:V ratio decreases by that same factor
Explain the properties of carbon nanotubes.
Answer in terms of structure and bonding
High tensile strength due to strong covalent bonds between carbon atoms
Good electrical conductors depending on the structure due to delocalised electrons that allow charge to flow throughout the structure
Small diameter, so can be used in nanotechnology. They also have a high surface area due to the tubular structure , which is beneficial for catalyst support
Chemically inert due to the strong carbon to carbon bonds, so are useful in applications such as in composite materials
Compounds made of simple molecules …
Do not conduct electricity even when they are molten or in solution UNLESS they react with the water to form aqueous ions. This is as there is no overall charge so their neutral molecules cannot carry electrical charge
Explain why polymers are solid at room temperature
The atoms in the polymer molecules are linked to other monomers by strong covalent bonds
There are also intermolecular forces between polymer molecules
This requires a lot of energy to overcome and so they have a high melting point and so are solids at room temperature
Give uses for each allotrope of carbon
