Chapter Four Flashcards
Metals
Properties of metals
- Range of melting points and relatively high boiling point
- Conductors of electricity
- Generally high densities
- Malleable
- Ductile
- Lustrous
- High tensile strength
- Low ionisation energies and electronegativities
What type of ions do metals form
Metals usually form cations as they lose their valence electrons to meet the octet rule
What are transition metals used for
- Bridges
- Cans
- Railway lines
Properties of transition metals
- Harder
- Higher densities
- Higher melting points
- Some have strong magnetic properties
- Greater core charge
- Atoms are smaller
- Stronger bonds
Iron
- Brittle and corrodes easily
- Mixed with carbon and other transition metals to make alloys such as steel
Lattice
Tightly packed arrangement
What do electrons do in metallic bonding
The electrons delocalise to form a ‘sea’ of electrons throughout the entire metallic structure which are strongly attracted to the metal cations
What does the metallic bonding model include
- Charged particles that are free to move andd conduct electricity
- Strong fforces of attraction between atoms throughout the metal structure
- Some electrons that are relatively easily removed
How are cations held in the lattice
Through strong electrostatic attraction between the cations and the electrons > it extends throughout the lattice
Why are metals dense
Cations are closely packed together
What is metallic bonding
The attraction between the positively charged ions and the delocalised electrons
Why are metals lustrous
Free electrons allow the metal to reflect light of all wavelengths and appear shiny
Why are metals good conductors of heat
When the metal is heated the delocalised electrons gain energy and vibrate more rapidly, by bumping into neighbouring electrons it allows for the rapid transmittance of energy throughout the lattice
Limitations of the metallic bonding model
- Range of melting points, hardness and densities of different metals
- Differences in electrical conductivities of metals
- Magnetic nature of some metals
Reactivity with acids
- Metals are normally more reactive with acids than water > the reactions tend to be more energetic
- E.G > Magnesium + hydrochloric acid -> magnesium chloride + hydrogen gas
Reactivity with water
- Metals in group one are more reactive with water than metals in group two
- Going down the group reactivity increases
Reactivity with oxygen
- Group 1 react rapidly
- Group 2 reacts just not as rapidly and heat is usually required
- Transition metals are less reactive than these two groups
- E.G > sodium + oxygen -> sodium oxide
Why does reactivity change
Due to the relative attractions of valence electrons to the nucleus of atoms
Ways of modifying metals
- Alloy production
- Heat treatment
- Formation of nano-sized structures
Alloys
- Metals are mixed with small amounts of another substance- usually a metal or carbon
- They are melted together, mixed and then allowed to cool
- Generally harder and melts at lower temperatures than pure metals
Interstitial alloys
When a small proportion of an element with significantly smaller atoms are added to a metal and the small atoms sit in the interstitial spaces between the metal cations
Substitutional alloy
- When elements with bigger atoms are added, they replace some of the cations in the lattice
- Similar chemical properties and form cations of a similar size to the main metal
What do malleability and brittleness depend on
Malleability and brittleness depends on size and arrangement of the crystals
Work hardening
- Hammering or working cold metals causes the crystals to rearrange as they are pushed and deformed
- Results in hardening of the metal as the crystals are flattened out and pushed closer together
Heat treatment
- When heated above critical temperatures individual crystals merge and re-form when allowed to cool
- The rate of cooling determines the size of crystals
Metallic nanomaterials
- Particles
- Rods
- Wires
- Tubes
Metallic nanoparticles
Nanoparticles that contain only 100 or so atoms have properties in between those of metals and non-metals > different optical properties and more sensitive to heat
Nanorods
Nanoscale rods > display technologies and microelectronics (solar cells + mobile phones)
Nanowire
- A nano sized wire
- Longer than nanorods
- Catalysts, electronics
Why are nanomaterials good for use
- Have unique electrical. catalytic, magnetic, mechanical, thermal and imaging characteristics
- Attractive for use in the medical, pharmaceutical, electronic and engineering sectors
Delocalised
Detached or removed from a particular place or location
