s2.3 metallic bonding Flashcards
what is metallic bonding?
metallic bonding is the electrostatic attraction between a lattice of positive ions and delocalised electrons
what are some metallic structures?
metals such as sodium, magnesium and gold are giant metallic lattices. this means that there are millions of cations forming a lattice structure held together by their attraction to delocalised electrons.
what are some properties of metals?
- lustre (shiny appearance)
- sonority (sound when struck)
- malleability (can be reshaped on compression)
- ductility (can be drawn out into a wire)
- electrical conductivity
- thermal conductivity
why are metals malleable?
malleability is the property which enables the metal to be hammered or pressed into any shape. layers of metals cations are able to slide over each other with the delocalised electrons staying intact
how does malleability differ in alloys?
the properties of a metal can be significantly altered by adding small amounts of another substance, usually a metal or carbon. the substances are melted together, mixed and then allowed to cool. the resultant solid is called an alloy.
the production of an alloy is possible due to the non-directional bonding of the delocalised electrons (to the cation lattice that can accommodate ions of different sizes). by inserting another element into the structure (i.e. in alloys), the layers can no longer slide over each other making it difficult for alloys to change their shape
why are metals good conductors of electricity?
electrical conductivity is the ability of a material to carry the flow of an electric current (flow of electrons). metals are good conductors of electricity as they have delocalised electrons.
how does electrical conductivity increase as you move along a period?
as the number of valence electrons increases for a metal, the number of delocalised electrons moving throughout the lattice increases. this increases the electrical conductivity of the metal.
gallium, Ga, is the element that is inconsistent with this trend. it is a metal but is close to the metalloids in the periodic table
why does electrical conductivity increase as you move along a period?
when a potential difference is applied to a metallic lattice, the delocalised electrons repel away from the negative terminal and move towards the positive terminal. as the number of outer electrons increases across a period, the number of delocalised charges also increases: therefore, the ability to conduct electricity also increases across a period
what are some common uses of metals?
iron: building frames - strong & relatively cheap
copper: water pipes & electrical circuits - unreactive, non-toxic, malleable, good conductor of electricity
aluminum: window frames - strong & light
why do metals have high melting points?
metals have high melting points due to strong metallic bonding (electrostatic attraction between positive cations and delocalised electrons). the stronger the metallic bond strength, the higher the melting point
how does the strength of a metallic bond change?
the strength of a metallic bond depends on the charge of the ions and the ionic radius of the metal ion.
metallic bond strength decreases as you go down a group. metallic bonding is weaker in potassium than in sodium: this is due to the potassium ions being larger than the sodium ions so the same amount of electron charge is spread over a larger volume.
metallic bond strength increases as you go across a period. metallic bonding is weaker in sodium than in magnesium: this is due to the sodium ions and magnesium ions having a similar size but in magnesium two valence electrons are delocalised (greater ionic charge).
