bonding, structure and properties Flashcards

1
Q

what is a compound

A

a compound is a substance which 2 or more elements are chemically combined

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2
Q

what are the three types of chemical bonds

A

ionic - bonding in ionic compounds

metalic - bonding in metals

covalent - bonding in giant covalent structures

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3
Q

what are the properties of ionic compounds

A

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

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4
Q

what are the properties of metallic compounds

A

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

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5
Q

what are the properties of simple molecular covalent substances

A

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

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6
Q

what are the properties of giant covalent substances

A

substances with a giant covalent structure are solids with very high melting points

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7
Q

explain the bonding and structure in metallic compounds

A

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

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8
Q

how does ionic bonding take place

A

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

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9
Q

how are covalent bonds formed

A

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

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10
Q

why do simple molecular substances have low melting and boiling points

A

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

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11
Q

what are the properties of diamond?

its bonding and structure

A

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

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12
Q

what are the properties of graphite

its bonding and structure

A

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

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13
Q

what are the properties of graphene

its bonding and structure

A

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

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14
Q

what are fullerenes

A

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

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15
Q

what are carbon nanotubes

A

cylindrical fullerenes with very high length to diameter ratios

the have very high tensile strength and conduct electricity due to the delocalised electrons present

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16
Q

do individual atoms have the same properties as bulk materials

A

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)

17
Q

what are the properties of nanoparticles

A

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

18
Q

what are the uses of nanoparticles

A

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

19
Q

what are the risks of nanoparticles

A

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

20
Q

what are the properties and uses of thermochromic materials

A

Change colour when you reach a certain temperature

Using mugs and spoons which change colour when the contents are hot

21
Q

what are the properties and uses of photochromic pigments

A

These pigments change colour when exposed to light

Used in sunglasses which darken in bright sun

22
Q

what are the properties and uses of polymer gels

A

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

23
Q

what are the properties and uses of shape memory alloys/polymers

A

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

24
Q

what is a smart material

A

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