bonding, structure and properties Flashcards
what is a compound
a compound is a substance which 2 or more elements are chemically combined
what are the three types of chemical bonds
ionic - bonding in ionic compounds
metalic - bonding in metals
covalent - bonding in giant covalent structures
what are the properties of ionic compounds
strong electrostatic attraction between oppositely charged ions means ionic compounds have HIGH MELTING AND BOILING POINTS
in a solid state, ionic compounds do not conduct electricity as ions are fixed in place
when ionic compounds are molten / dissolved, ions can move around so then ionic compounds conduct electricity
they are BRITTLE
what are the properties of metallic compounds
the layers pf ions in metallic compounds are able to slide over each other, so metals are malleable and ductile
the delocalised electrons can move through the metal and carry charge, so metals conduct electricity and heat
metallic bonds are very strong and require large amounts of energy to be broken, giving most metals high melting and boiling points
what are the properties of simple molecular covalent substances
simple molecules (e.g. oxygen) have week intermolecular forces between molecules, so they have low melting and boiling points
simple molecular covalent substances do not conduct electricity because simple molecules do not have an overall charge
they are usually gas or liquids
what are the properties of giant covalent substances
substances with a giant covalent structure are solids with very high melting points
explain the bonding and structure in metallic compounds
The electrons in the outer shell metal atoms are delocalised and so they are free to move through the whole structure – sea of delocalised electrons
Metallic bonds formed due to the electrostatic attraction between the positively charged metal ions and the negatively charged delocalised electrons
how does ionic bonding take place
Electrons in the outer shell of the metal are transferred
Metal atoms lose electrons to become positively charged ions
Nonmetal atoms gain electrons to become negatively charged ions
The electrostatic attraction family obviously charge ions form is a giant ionic lattice
The electron transfer can be represented by dot and cross diagram
how are covalent bonds formed
When atoms share pairs of electrons, they form covalent bonds
the bond between these atoms are strong
dot and cross diagrams can be drawn to represent the sharing of electrons
why do simple molecular substances have low melting and boiling points
Weak intermolecular forces between molecules – these are broken in melting or boiling, not a strong covalent bonds
The intermolecular forces increase with the size of the molecules, larger and molecules have high melting and boiling points
what are the properties of diamond?
its bonding and structure
It is very hard, had a very high melting point and does not conduct electricity
Each carbon is joined to 4 other carbons covalently - covalent bonds need a lot of energy to be broken which results in very high melting points
This is the maximum number of bonds each carbon atom can make
what are the properties of graphite
its bonding and structure
Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings which have no covalent bonds between the layers
The layers can slide over each other due to the absence of covalent bonds between the layers, but they are weak intermolecular forces between the layers – so graphite is soft and slippery
One electron from each carbon atom is delocalised so it can conduct electricity
what are the properties of graphene
its bonding and structure
Its structure resembles a single layer of graphene
graphene has a very high melting point due to the very strong covalent bonds between the carbon atoms that require large amounts of energy to be broken
Conducts electricity due to the delocalised electrons that are free to move through its structure
what are fullerenes
Molecules of carbon with hollow shapes
They are based on hexagonal rings of carbon atoms, but they may also contain rings with five or seven carbon atoms
what are carbon nanotubes
cylindrical fullerenes with very high length to diameter ratios
the have very high tensile strength and conduct electricity due to the delocalised electrons present
do individual atoms have the same properties as bulk materials
no - for example, carbon atoms on their own do not have any of the properties exhibited by any of the different structures (diamond, graphene, nanotubes or fullerene)
what are the properties of nanoparticles
1–100 nanometers across
Contain a few hundred atoms
They have different properties from the bulk properties which they form because of the high surface area to volume ratio
what are the uses of nanoparticles
nano-silver - kills bacteria: used in wound dressing, deodorant, or to line socks and fridges to kill bacteria causing bad smell
nano-titanium - used in sun block creams to block harmful UV rays without appearing white on the skin as the particles do not reflect visible light, also used except cleaning windows as they help break down dirt
what are the risks of nanoparticles
So small that they could potentially end of the bloodstream
Relatively new material so long time affects are not known
Can enter and potential damage to environment
what are the properties and uses of thermochromic materials
Change colour when you reach a certain temperature
Using mugs and spoons which change colour when the contents are hot
what are the properties and uses of photochromic pigments
These pigments change colour when exposed to light
Used in sunglasses which darken in bright sun
what are the properties and uses of polymer gels
Hydrogels episode back to 1000 times the value in water
Certain stimuli (changes in pH and temperature) can cause the water to be released
Used in nappies, fake snow and hair gel
what are the properties and uses of shape memory alloys/polymers
These materials can be bent and deformed but will return to their original shape when heated
Shape memory polymers are used in medical stitching and sports equipment such as gumshield
Shape memory alloys are used in car bodies and plates for bone fractures
what is a smart material
A material that can change when the environment changes
the change a smart with your mates is reversible
the one more properties can be changed by an external condition
