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).
what is thermal conductivity?
thermal conductivity is a measure of a material’s ability to transfer heat as a result of a temperature difference.
why do metals have a high thermal conductivity?
when metals are heated, the cations in the metal lattice vibrate more vigorously as their thermal energy increases.
these vibrating cations transfer their kinetic energy as they collide with neighbouring cations, effectively conducting heat.
when the cations vibrate, they transfer kinetic energy to the electrons. the delocalised electrons then carry this increased kinetic energy and transfer it rapidly throughout the metal, contributing to its high thermal conductivity.
how does thermal conductivity differ between groups?
metals in group 2 have higher thermal conductivities than those in group 1 due to a greater number of delocalised electrons increasing the thermal conductivity of the metal.
group 13 metals would be expected to have a higher thermal conductivity than group 2. however group 12 metals are actually observed to have a lower thermal conductivity.
one theory for this inconsistency is that as heat is added, the electrons experience greater collisions with each other, causing them to slow down and reduce the thermal conductivity.
what are transition metals?
a transition metal is an element that can form at least one stable cation with an incomplete d-subshell. transition elements are found in the d block of the periodic table.
in reactions, d block elements lose electrons to form positive cations. the electrons are lost from the 4s orbital before the 3d orbital (with chromium and copper being the exceptions).
this definition distinguishes transition metals from d block elements because scandium and zinc do not fit the definition - they don’t form stable ions.
what is the structure of transition metals?
like other metals, transition metals have a giant metallic lattice structure. since the 3d and 4s subshells are so close in energy, the transition metals are able to delocalise their d-electrons to form metallic bonds. this causes transition metals to have particularly good electrical conductivity and high melting points.
why do transition metals have high melting points?
transition metals have a higher melting point than s and p block metals. the ability to delocalise the d-electrons (increased ionic charge) means that transition metals have a greater electron density. this is despite the fact that the cations are larger (increase in ionic radius) in transition metals.
this means that the electrostatic forces of attraction between the cations and the delocalised electrons are strengthened. the stronger forces of attraction result in a higher melting point as more energy is required to overcome them.
why are transition metals good conductors of electricity?
transition metals are very good conductors of electricity due to their delocalised d-electrons. the three most conductive metals are:
- silver
- copper (most used metal in electrical cables due to a combination of cost and conductivity)
- gold
what are some other properties of transition metals?
although the transition elements are metals, they have some properties unlike those of other metals on the periodic table (due to their incomplete d subshell), such as:
- variable oxidation states
- have magnetic properties, due to the presence of unpaired electrons in the d orbitals
- catalysts
- form coloured compounds
- form complex ions with ligands.
