S2.3 Metallic Model & S2.4 Models to Materials

S2.3 Metallic Model &
S2.4 Models to Materials

​Nature of Metallic Bond

​Electrostatic attraction between a lattice of cations and delocalized electrons.

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Ionic bonds are electrostatic attractions between ​

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and ​​

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. Covalent bonds are electrostatic attractions between positively charged ​

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and shared ​

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. Metallic bonds are electrostatic attractions between ​

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and delocalised electrons.

​Properties of Metals

​Metals are malleable because:

• cations can slide past each other without disrupting bonding

• attraction between metal ions and delocalized electrons/metallic bonding is not disrupted by changing position of metal ions

• metallic bonds are non-directional, so changing the shape does not disrupt the bonding

​Electrical Conductivity

Metals conduct electricity because electrons are delocalised and therefore able to flow (freely moving charged particle)

​Note: Current flow occurs without displacement of atoms within the metal

​Thermal Conductivity

​Metals conduct thermal energy because the delocalized electrons transfer energy more quickly throughout the material.

See video in next slide.

​Metallic Bonding Factors: Ion Radius

​↑ energy levels

= ↑ distance between cations & delocalized electrons

= weaker attraction (metallic bonding)

= lower melting / boiling point

​Metallic Bonding Factors: Ion Radius

​Ex: Lithium has a higher melting point because the lithium ion has one less energy level than the sodium ion. This results in the cations and electrons being closer together in lithium, resulting in stronger attraction. Therefore it takes more energy to overcome the attraction in lithium, resulting in a higher melting  point.

Multiple Choice

Which would have a higher melting point?

• Ca

• Mg

Drag and Drop

In order from highest melting point to lowest: ​

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> ​

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> ​

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> ​

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Drag these tiles and drop them in the correct blank above

Li

Na

K

Cs

​Metallic Bonding Factors: Cation Charge Magnitude

​↑ cation charge

= ↑ delocalized electrons

= stronger attraction (metallic bonding)

= higher melting point

​Metallic Bonding Factors: Cation Charge Magnitude

​Magnesium has a higher melting point because it has a 2+ charge, while Na has a 1+ charge. The higher charge magnitude leads to stronger attraction (metallic bonding) to the delocalized electrons. The higher charge also means there are more delocalized electrons in magnesium, resulting in stronger attraction.

​Melting Point Trends:

​GROUP TREND: As you go down a ground, melting points decrease due to a larger number of energy levels increasing the distance between the cations and delocalized electrons, resulting in weaker metallic bonding.

​Melting Point Trends:

PERIOD TREND: In general as you go to the right, melting points increase due to ion charges increasing.

​Note: Melting points are in the data booklet, so you can refer to them during the exam.

Multiple Choice

Which would have a higher melting point?

• Li

• Be

Multiple Choice

Why does calcium have a higher melting point than strontium?

• Calcium has weaker metallic bonds due to its larger ionic radius.

• Strontium has stronger metallic bonds due to its smaller ionic radius.

• Calcium has a lower melting point its smaller ionic radius.

• Calcium has stronger metallic bonds due to its smaller ionic radius.

• Calcium has stronger metallic bonds due to having a higher ionic charge.

​HL: Transition Metal Properties

​Delocalized d-electrons lead to higher conductivity and higher melting points compared to s-block elements.

Multiple Choice

Why does iron have a higher melting point than calcium?

• Iron has a higher melting point than calcium because it has network covalent bonding.

• Iron has a higher melting point than calcium because it has delocalised d-sublevel electrons that give stronger metallic bonding.

• Iron has a higher melting point than calcium because it has a lower ion charge.

• Iron has a higher melting point than calcium because it has fewer electrons.

​Examples of Alloys

​Most metals in our daily lives are not pure metals, but homogeneous mixtures of metals called alloys.

​Alloy Properties

​Alloying elements disrupts regular metal lattice.

• difficult for one layer to slide over another;

• can make metal harder/stronger/more corrosion resistant.

• decreases melting point as the disruption of the lattice weakens the metallic bonding

Categorize

Options (5)

Melting Point

Strength

Hardness

Corrosion Resistance

Order/regular patterns of metal lattice structure

Sort how each property is affected by alloying.

Increases

Decreases

​Bonding Triangle

​The three intramolecular bonding types can be arranged on a triangle & the properties are summarized in this chart. Once you know the type of bonding the substance has, you can predict its properties.

​Bonding and Electronegativity

​Bond types can be determined by electronegativities of atoms involved. This is found in your data booklet:

Draw

Draw an X on the bonding triangle showing where H₂O would be found.

Draw

Draw an X on the bonding triangle showing where AlCl₃ would be found.

Draw

Draw an X on the bonding triangle showing where an alloy of copper and zinc would be found.

Multiple Choice

A compound has an electronegativity difference of 2.1 and average electronegativity of 1.9. What property would you expect?

• Conduct electricity in the solid state.

• Not conduct in any states.

• Conduct electricity in aqueous or molten state.

• Only certain allotropes of the compound to conduct electricity.