topic 2 - bonding, structure and the properties of matter (flashcards)

types of chemical bonds

• ionic

• covalent

• metallic

why does bonding occur?

atoms with incomplete outer electron shells are unstable. By forming bonds, atoms can completely fill their outer shell and become stable.

ionic bonding

• metals combined with non-metals

• metal atoms lose an electron to become positively charged ions → non-metal atoms gain an electron to become negatively charged ions

• the oppositely charged ions are held together by strong electrostatic attractions

ionic compounds

• millions of ions packed together in a cubic arrangement - forming a giant 3D structure called an ionic lattice

• requires a lot of heat energy to break the bonds → solid at room temperature and high melting point

• does not conduct electricity when solid - ions cannot move

• when molten, lattic breaks and ions are free to move

• ionic compounds are usually soluble in water

• brittle - shatter when hit

covalent bonding

• occurs in non-metallic atoms, which share one or more pairs of electrons

• when non-metal atoms react together, they need to gain an electron to fill their outer shell and become stable

• atoms can share 2, 4 or 6 electrons

simple covalent structures

• they only contain a few atoms

• most molecular substances are gas or liquid at room temperature → they have weak intermolecular forces that only require a small amount of energy to break

properties of molecular substances

• low melting point and low boiling point (weak intermolecular forces)

• usually insoluble in water

• cannot conduct electricity - no free electrons to carry an electrical charge

• brittle

giant covalent structures

consists of millions of atoms joined together by covalent bonding e.g. diamond, silicon dioxide.

structure of a diamond

each atom is covalently bonded to four others

properties of diamond

• very hard - each carbon atom is bonded to four others, forming a very rigid 3D structure

• high melting point and boiling point - a lot of energy is needed to break many strong covalent bonds

• cannot conduct electricity - no free electrons or mobile ions to carry a charge

sand (silicon dioxide)

• impure form of silicon dioxide (quartz)

• each silicon atom is bonded to four oxygen atoms

• each oxygen atom is connected to two sillicon atoms

• giant covalent structure with similar properties to diamond

structure of graphite

• each carbon atom is bonded to three others

• forms rings of six atoms, creating a giant structure, containing many layers - layers are held together by weak forces of attraction

properties of graphite

only three of the four electrons in the outer shell of the carbon atom are used in covalent bonds

• graphite is soft and slippery - layers can easily slide over each other because the weak forces of attraction are easily broken → this is why graphite can be used as a lubricant

• conducts electricity (only non-metal to do so)

• high melting and boiling point

buckminsterfullerene

• contains 60 carbon atoms, each bond with three others - forming two single bonds and one double bond

• can be used for drug delivery into the body, in lubricants, to reinforcing materials and as catalysts

what are carbon nanotubes and their properties?

• cylinder fullerenes

• high tensile strength that reinforce composite materials

• high electrical and thermal conductivity

graphene

• form of carbon, consisting of planar sheets (one atom thick)

• atoms arranged in honeycomb-shaped lattice

why are fullerenes good catalysts?

they have a large surface area compared to their volume

metallic bonding

• atoms of metals are tightly packed together in a giant lattice

• outer electrons separate from their atoms and become delocalised, creating a ‘sea of electrons’

• atoms become positive ions and are attracted to these electrons

properties of metals

• dense - metal ions are tightly packed

• high melting and boiling point - metallic bonds are very strong

• tough - when a metal is hit, the layers of the lattice just slide over each other

• malleable - can be bent + pressed into shape

• ductile - can be drawn out into wires

metals are good conductors of…

• heat - they can transfer thermal energy throughout the lattice by free electrons

• electricity - electrons are free to move and can carry electrical charge

nanoparticles properties

• electrons can move through insulating layers of atoms

• more sensitive to light, heat & magnetism

• silver and able to kill bacteria

disadvantages of nanoparticles

• difficult to engineer

• can be dangerous