1
Q
PROPERTIES OF IONIC BONDS 5 POINTS PLUS EXAMPLES
A
- Non Conductors of electricity IN A SOLID STATE
- Conductors of electricity IN A MOLTEN STATE AND WHEN DISSOLVED IN WATER
- Hard and Brittle
- High Melting point
- Soluble in polar solvents
- Eg. Magnesium Iodide (MgI2), Zinc Sulfate (ZnSO4), Sodium Chloride (NaCl)
2
Q
PROPERITIES OF METALLIC BONDS 4 POINTS PLUS EXAMPLES
A
- Conductors of electricity IN A SOLID
- Conductors of electricity MOLTEN STATE
- Malleable and Ductile
- Moderate to High melting points
- Generally insoluble in liquids
- Eg. Copper (Cu), Gold (Au), Aluminimum (Al), Iron (Fe), Nickle (Ni), Titanium (Ti)
3
Q
PROPERTIES OF COVALENT MOLECULAR 6 POINTS PLUS EXAMPLES
A
- Non Conductors of electricity in a SOLID STATE
- Non Conductors of electricity in a MOLTEN STATE
- Non Conductors of electricity when DISSOLVED IN WATER
- Exceptions; Covalent Molecular Acids (HCl, HNO3, H2S04) which are GOOD CONDUCTORS IN DISSOLVED WATER
- Soft
- Soluble in polar or non polar solvents
- Low melting points
- Eg. Carbon Dioxide (CO2), Water (H2O), Sugar (C12H22O11)
4
Q
PROPERTIES OF COVALENT NETWORK
A
- Non Conductors of electricity in a SOLID STATE
- Hard and Brittle
- Very High Melting Points
- Insoluble in all solvents
- Eg. Silicon (Si), Silicon Dioxide (ie. quartz, SiO2), Diamond and Graphite
5
Q
WHY METALLIC SUBSTANCES ARE GOOD CONDUCTORS OF ELECTRICITY
A
- Valence electrons that form the SEA OF ELECTRONS are move
- Electrons an move freely throughout the metallic lattice
- If voltage is applied to a metal, electrons from the mobile sea move towards the positive terminal of the power supply
- Positive metal ions remain stationary in their fixed positions
- The ability of the valence electrons to move thus to conduct charge = good conductors of electricity
6
Q
WHY METALLIC SUBSTANCES ARE GOOD CONDUCTORS OF HEAT
A
- Electrons without sea of electrons are mobile
- Means thy can carry heat energy (as kinetic energy) throughout the metal lattice
- Vibration of metallic ions also contributes to the flow of heat through the metal lattice
7
Q
WHY METALLIC SUBSTANCES ARE MALLEABLE AND DUCTILE
A
- Bonding between metal ions and the sea of electrons is NON-DIRECTIONAL
- Means individual metal atoms can move in relation to each other without breaking the bonds between them and the sea of electrons
- Allows metal to change SHAPE, BEND OR STRETCH without breaking
8
Q
HIGH MELTING AND BOILING POINTS
A
- Strong attractive forces between the metal ions and the sea of electrons hold the LATTICE TOGETHER
- Thus, high temperature is needed to disrupt the lattice and allow the metal to melt
9
Q
IONS WITHIN A METALLIC SUBSTANCE
A
- Positive ions occupy FIXED positions
- Valence electrons released from the metal atoms are FREE to move at RANDOM amongst the lattice of metal ions
- Electrons are; DELOCALISED, MOBILE SEA OF ELECTRONS
10
Q
BONDING IN METALLIC SUBSTANCES
A
- STRONG due to electrostatic attraction between the positive ions and the mobile sea of electrons
- Non-Directional; as they occur equally in all directions between all the metal ions and the sea of electrons
11
Q
ELECTRON-SEA MODEL
A
- Accounts for the conductivity of metals in terms of the metal VALENCE ELECTRONS that form the ‘sea of mobile electrons’
- These MOBILE ELECTRONS readily conduct heat and electrical energy through the metallic structure
12
Q
IONIC COMPOUNDS
A
- Between Non Metal and Metal
- Eg. NaCl, CaO, MgSO4, Al(NO3)3, NH4Cl
- Metal element in the compound LOSES its valence electrons to form a POSITIVE ION with FULL VALENCE OUTER SHELL
- Lost electrons ar transferred to the non-metal elecemtn that forms a NEGATIVE ION with FULL VALENCE OUTER SHELL
13
Q
IONIC LATTICE
A
- Ionic Compounds result in IONIC LATTICE
- BONDING IN A IONIC LATTICE; strong due to electrostatic attraction between positive and negative ions
14
Q
WHY IONIC COMPOUNDS ARE POOR CONDUCTORS OF ELECTRICITY WHEN SOLID
A
- When solid; the ions are TIGHTLY held in FIXED positions within the lattice, thus unable to move and carry charge
- Absence of MOBILE CHARGED PARTICLES
15
Q
WHY IONIC COMPOUNDS ARE GOOD CONDUCTORS OF ELECTRICITY WHEN MOLTEN
A
- When molten; ions are mobile, free to move and carry charge throughout ionic liquid
- BOTH positive and negative ions carry charge
- Positive ions move towards the negative electrode and vice versa
16
Q
WHY IONIC COMPOUNDS ARE GOOD CONDUCTORS OF ELECTRICITY WHEN IN AQUEOUS SOLUTION
A
- When aqueous; individual ions from the ionic solid are MOBILE and FREE to move independently of one another
- Mobility and charge enable them to conduct electric current through ionic solution
- BOTH positive and negative ions are involved in conducting the current
- Current consists of positive ions moving toward the negative electron and vice versa
17
Q
WHY IONIC COMPOUNDS ARE HARD AND BRITTLE
A
- When a large force is applied to the ionic lattice, the ions move
- Charged ions will be forced to align alongside each other ie. no longer aligned diagonally
- This means like charges will be closer together than unlike charges
- Consequently repulsive forces will exceed attractive forces and the lattice will break apart rather than simply dent or bend
18
Q
WHY IONIC COMPOUNDS HAVE HIGH MELTING AND BOILING POINTS
A
- Ionic bonds are strong electrostatic attractive forces between ions
- These strong attractive forces extend throughout the ionic lattice keeping individual ions in fixed positions
- Thus a higher temperature ie. high particle kinetic energy is needed to disrupt (melt) the ionic lattice
19
Q
COVALENT BONDING
A
- Occurs between non metal elements
- Valence electrons are shared between the bonded atoms so that each atom has a full outer shell
20
Q
COVALENT BONDS
A
- Directional
- A single covalent bond is aligned along an axis through the two atoms that share electrons
- Bonding in electrons are LOCALISED along this axis and between the two bonded atoms
- Occur in substances; covalent molecular or covalent network
21
Q
COVALENT MOLECULAR SUBSTANCES
A
- Eg. most non-metal elements; chlorine (Cl2), Oxgen (O2), Nitrogen (N2) and most compounds formed from a combination of non-metals only; CH4, HBr, NH3 and H2SO4
- In covalent molecular substances, small groups of atoms become covalently bonded to one another forming CLUSTERS OF ATOMS KNOWN AS MOLECULES
- Strong covalent bonds within the molecules are referred to as INTRAMOLECULAR FORCES
- Weak attraction forces between the molecule are known as INTERMOLECULAR FORCES
22
Q
WHY COVALENT MOLECULAR SUBTANCES ARE NON CONDUCTORS OF ELECTRICITY IN A SOLID/LIQUID/AQUEOUS PHASE
A
- Electrons in a covalent molecular substance are localised within each atom’s electron cloud or as shared electrons within covalent bonds
- Non of these electrons are FREE to move independently
- Substances DONT contain ions
- Absence of freely mobile charged particles = non conductors of electricity
23
Q
WHY SOME COVALENT MOLECULAR SUBSTANCES ARE GOOD CONDUCTORS OF ELECTRICITY WHEN IN AQUEOUS SOLUTION
A
- Covalent molecular substances which or ACIDIC OR BASIC eg. HCl, H2SO4 and NH3 REACT with water (ionise) producing free mobile ions
- Resulting ions are able to move freely throughout the solution carrying charge = conducting an electric current
24
Q
WHY COVALENT MOLECULAR SUBSTANCES ARE SOFT AND WEAK
A
- Strong covalent bonds (INTRAMOLECULAR FORCES) only form between the atoms within molecules
- Only WEAK INTERMOLECULAR FORCES of attraction occur between neighbouring molecules
- Consequently molecules are easily separated from one another, making them weak and soft
25
WHY COVALENT MOLECULAR SUBSTANCES HAVE LOW TO MODERATE MELTING AND BOILING POINTS
- When a molecular substance melts or boils, only the WEAK INTERMOLECULAR FORCES need to be broken or overcome
- Thus weakly bonded lattice of molecules in the solid phase is easily disrupted by heat energy to form a liquid or gas
- Strong covalent bonds occurring between atoms within the molecule (INTRAMOLECULAR FORCES) are unaffected when substance melts or boils
26
COVALENT BONDING IN POLYATOMIC IONS
- Many ionic compounds contain one or more polyatomic ions
- Whilst these ions form part of an IONIC compound, the atoms within the polyatomic ion are COVALENTLY bonded to each other
- Arrangement of valence electrons in a polyatomic ion can be shown using a Lewis Structure
27
COVALENT NETWORK SUBSTANCES
- Eg. Boron (B), Carbon (C), Graphite, Diamond, Silicon (Si), Silicon Dioxide (SiO2 ie. quartz or sand) and Silicon Carbide (SiC)
- Atoms in these substances form covalent bonds with multiple neighbouring atoms resulting in a CONTINUOUS ARRAY OF COVALENTLY BONDED ATOMS
- Different to MOLECULAR as the strong covalent bonding extends continuously throughout the substance
- Gives structure gives covalent network substances properties that contrast strongly with those of covalent molecular materials
28
CARBON ALLOTROPES
- Different forms of the same element
| - Eg. Graphite and Diamond both consist of PURE CARBON
29
WHY COVALENT NETWORK SUBSTANCES ARE NON CONDUCTORS OF HEAT OR ELECTRICITY
- Electrons in these substances are held in FIXED positions within the atom's shells, lone pairs or covalent bonds-
- Electrons ARENT free to move independently means they conduct electricity or heat through the substance
- GRAPHITE (carbon allotrope) is AN EXCEPTION of this, as some valence electrons are delocalised (free to move)
30
WHY COVALENT NETWORK SUBSTANCES ARE VERY HARD AND BRITTLE
- Strong covalent bonds occur between all atoms within a covalent network
- This CONTINUOUS ARRAY OF STRONGLY BONDED ATOMS is difficult to disrupt = hard and brittle
- GRAPHITE IS AN EXCEPTION TO THIS
31
WHY COVALENT NETWORK SUBSTANCES HAVE VERY HIGH MELTING AND BOILING POINTS
- Strong covalent bonds occur between all atoms within the structure
- A very high temperature (high kinetic energy) is needed to disrupt this continuous array of strongly bonded atoms
32
WHAT IS A NANOPARTICLE? AND INCLUDE EXAMPLES THAT DON'T INVOLVE CARBON
- Particles with ATLEAST one dimension in the 1-100 nanometre range (ie 1-100x10-9m)
- Quantum dots are nanoparticles typically made form ZnS or ZnSe
- Some sunscreens contain nanoparticles of ZnO or TiO2
33
NANOPARTICLES OFTEN EXHIBIT QUANTUM EFFECTS.WHAT IS MEANT BY A QUANTUM EFFECT APPLIED TO NANOPARTICLES PLUS EXAMPLE
- Nanoparticles often have properties that differ greatly from those of the bulk material of which they are
- Due to Quantum Effects
- These result from their small particle size
- Zinc Oxide (example) are opaque and white, however when prepared as nanoparticles they become colourless and invisible
- Nanoparticle size samples of ZnSS or CdSe (quantum dots) exhibit a variety of colours when exposed to UV light
- This doesn't happen to a bulk sample of ZnS or CdSe
34
DESCRIBE THE STRUCTURE OF A DENDRIMER AND EXPLAIN WHY ITS CALLED A NANODEVICE RATHER THAN A NANOPARTICLE
- A dendrimer is a nanoparticle that can be used as a molecular carrier
- In this example the dendrimer will carry four molecules, one that recognises cancer cells, another that is a therapeutic agent able to kill cancer cells, a third molecular which recognises when the cancer cell dies and a fourth molecule that signals the cancel cells death
- The resulting dendrimer package is called a nanodevice as it has several components that act togheter to produce an outcome
- Ie. its considered a device which as a nanoscale size
35
LASER ABLATION (PRODUCES NANOPARTICLES)
- Involved using high powered pulses to vaporise a graphite target in an inert atmosphere
- The vaporised carbon atoms called as CNT's on a water cooled collector surface
- A small amount (around 1%) of a metal catalyst such as Ni/Co may be incorporated in the graphite target to enhance the process
- The laser ablation method has alose been used to create single walled CNT's covered with quantum dot lead sulfide particles
- Other techniques include solution evapouration, chemical vapour deposition, microbial synthesis and chemical precipitation from solution
36
FULLERENES
- CNT's
| - C60
37
WHAT IS A NANOCOMPOSITE? USE EXAMPLE
- Nanocomposites are made by adding nanosized particles of one material to a matrix of a bulk material such as metal, polymer or ceramic (eg concrete)
- Modern nanocomposite applicaties inolved the addition of manufactured nanotubes or graphene to plastics like polyprotylene, polycarbonate and epoxy resins
38
WHY ARE NANOCOMPOSITES POTENTIALLY SUPERIOR TO FIBERGLAS AND CARBON FIBRE PLASTICS?
- Nanocomposites can have enhanced or modified properties such as a lower density, improved mechincal strength, electrical and thermal conductivity, catalytic and optical properties that are superior to those of traditional composites like fibreglass or carbon fibre reinforced plastics
