Chemistry C2

how do ions form bonds

transferring electrons and forming 2 ions with opposite charges that are attracted to each other by electrostatic forces

how do 2 non-metals form bonds

covalent bonding shares electrons

chemical bonds

bonds between atoms in an element or compound

properties of covalent bonds

strong bonds between atoms, weak intermolecular forces between molecules

allotrope

a different structural form of the same element in the same physical state

properties of diamond

very strong, high melting/boiling point, doesnt conduct electricity

why does diamond have a high melting/boiling point

because it has many strong covalent bonds that require lots of energy to break

ionic compounds

giant lattice structures held together by strong electrostatic forces of attraction between oppositely charged ions. the forces act in all directions

properties of ionic compounds

high melting and boiling points to break apart the ionic bonds, cannot conduct electricity in solid form due to fixed positions and a lack of free electrons, but can when molten or dissolved in water

properties of substances made of small molecules

have relatively low melting and boiling points (weak intermolecular forces holding the molecules together), intermolecular forces increase with molecule size, there is no overall electric charge and no free electrons, so the substance cannot conduct electricity

diamond

very hard (giant lattice structure)

each carbon atom forms 4 covalent bonds (strong)

no free electrons

polymer

a large molecule formed by link many smaller molecules (monomers) together. bonds between the atoms in polymers are covalent and there are relatively strong intermolecular forces between the large molecules, making polymers solid at room temperature

giant covalent structures

solids with very high melting points as all the atoms are linked to each other by covalent bonds

molecules have

covalent bonds

properties of graphite

soft, high melting/boiling point, conducts electricty

why is graphite soft

layers of graphite have no covalent bonds between them

why does graphite conduct electricity

each carbon atom is only bonded to 3 other carbons meaning each carbon atom had 1 delocalised electron that is free to move around and carry electric charge

silicon dioxide (silica)

hard (giant lattice structure)

each silicon atom is covalently bonded to 2 oxygen atoms

no free electrons

high/melting boiling points (covalent bonds)

properties of graphene

conducts electricity like graphite

uses of fullerenes

acts as a cage to transport drugs around the body (it is hollow, unreactive and non toxic)

large sa:v ratio means they can be used as industrial catalysts

used in electronics

used to strengthen things without adding much weight (large length:diameter ratio)

limitations of using models to show bonding and state changes

particles are shown as solid spheres when they are almost all empty space

forces are not shown or shown as lines when in reality particles either have forces between them or are bonded together

particles are not usually shown as bonded, but different bonds exist between particles eg ionic

particles not moving, they move/vibrate

buckminster fullerene

each carbon atom is bonded to three others. there are free electrons that can move over the surface, but not between molecules so poor electrical conductor. good lubricant because the molecules can roll

structure and bonding in metals

giant structures of atoms / ions, electrons in the outer shell are delocalised, creating a ‘sea’ of delocalised electrons that holds metal ions together and makes strong metallic bonds

why are metals good conductors of heat?

energy is transferred by the delocalised electrons

why are alloys harder than pure metals

in pure metals, atoms are arranged in layers which can slide over each other. alloys are mixtures of metals or metal and non-metals, distorting layers by using other atoms so they dont slide over each other

nanotubes

contain hexagonal rings in a cylindrical tube shape, high length to diameter ratios (long and thin), each carbon is bonded to 3 others, can conduct electricity because delocalised electrons can flow and carry charge through the structure

uses of nanotubes

electronics - circuits in computers or wiring in aircrafts, making the aircraft much lighter and burning less fuel

materials - tennis rackets, bike frames (light and strong)

nanotechnology

nanoscience

structures that are 1-100 nm in size

nanoparticles are only a few hundred atoms in size

size of nanoparticles

1 to 100nm (1 × 10^-9 m)

size of fine particles (PM2.5)

1 × 10^-7 to 2.5 × 10^-6 m

size of coarse particles (PM10) often called dust

2.5 × 10^-6 to 1 × 10^-5 m

the smaller the size of particles

the bigger the surface area to volume ratio

uses of nanoparticles

cosmetics and suncreams, deodrants, electronics, medicine, catalysts

smaller quantities may be needed than for materials with normal sized particles thanks to the very large surface area to volume ratio of nanoparticles

nanoparticles in suncreams

uv absorbing nanoparticles (smaller amount of suncream, absorb more uv rays)

antibacterial uses of nanoparticles

silver nanoparticles can kill bacteria eg in socks

nanoparticlee in catalysts

smaller mass of catalyst for chemical reactions with big effect because of the big surface area to volume ratio

risks of nanoparticles

might be able to get into body cells and cause damage

long term effects may not yet be known