New
New
Year 10
OCR
Foundation

Using models to explain state changes

I can explain why there is a difference in melting/boiling points between simple and giant covalent structures, and use models to show the shapes and structures of covalent substances.

New
New
Year 10
OCR
Foundation

Using models to explain state changes

I can explain why there is a difference in melting/boiling points between simple and giant covalent structures, and use models to show the shapes and structures of covalent substances.

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Lesson details

Key learning points

  1. Molecular modelling represents the bonding and structure of substances.
  2. The way giant covalent structures melt/boil is very different to simple molecules.
  3. Diamond is very hard, has a very high melting point and does not conduct electricity, every atom is bonded to another.
  4. In graphite each atom is bonded to three others to form layers of hexagonal rings. Each atom contributes a free electron
  5. Simple molecules are held together by intermolecular forces, no chemical bonds hold them together.

Common misconception

Covalent bonds break in simple molecules for substances to melt/boil, because this happens in giant covalent structures.

Highlight that bonds require large amounts of energy to break, hence the very high melting points of diamond and graphite. As all atoms are bonded these must be broken to melt/boil.

Keywords

  • Simple molecular - Simple molecular substances are made up of two or more atoms covalently bonded together to form a distinct unit.

  • Model - Scientists use models to represent parts of the natural world that are too difficult to observe or explain directly.

  • Intermolecular force - Intermolecular forces are weak forces of attraction between molecules and molecular substances.

  • Giant covalent - A giant covalent substance has a large regular arrangement of atoms all joined together by covalent bonds.

Use models and encourage the use of molecular modelling kits to get students to understand the differences between simple molecules and giant covalent structures.
Teacher tip

Equipment

Molecular modelling kits.

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Video

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6 Questions

Q1.
Below, there are six different models for representing the bonding and structure in the compound ethane. Match the image to the correct type of model.
An image in a quiz
Correct Answer:a,dot-and-cross diagram

dot-and-cross diagram

Correct Answer:b,molecular formula

molecular formula

Correct Answer:c,ball-and-stick model

ball-and-stick model

Correct Answer:d,empirical formula

empirical formula

Correct Answer:e,displayed formula

displayed formula

Correct Answer:f,space-filling model

space-filling model

Q2.
What do the dots and crosses typically represent in dot-and-cross diagrams?
Correct Answer: electrons
Q3.
Which of the following are limitations of the empirical formula when representing molecules?
Correct answer: it does not show the types of bonds
Correct answer: it does not indicate the actual number of atoms
Correct answer: it does not provide any spatial information
it serves as a step towards determining the molecular formula
Q4.
Which model would not be appropriate to represent the bonding and/or structure in metals?
ball-and-stick
space-filling
Correct answer: dot-and-cross
delocalised "sea" of electrons
Q5.
What advantage does the ball-and-stick model have over the space-filling model?
It shows the actual size of atoms more accurately.
Correct answer: It clearly shows which atoms/ions have bonded.
It is easier to see the overall shape of the substance.
It is more accurate in depicting electron sharing.
Q6.
Which representation is most suitable for illustrating the arrangement of ions in a giant ionic lattice?
molecular formula
Correct answer: ball-and-stick model
displayed formula
empirical formula

6 Questions

Q1.
Which properties of diamond are explained by the fact that each carbon atom is strongly bonded to four other carbon atoms in a rigid structure?
electrical insulator
Correct answer: high melting point
Correct answer: very hard
Q2.
What type of forces hold simple molecules together?
covalent
ionic
Correct answer: intermolecular
metallic
Q3.
One model of graphite shows it having free moving, delocalised electrons. This means graphite is an electrical ?
Correct Answer: conductor
Q4.
Match each substance to the correct statement about it's structure and/or properties.
Correct Answer:diamond,doesn't conduct electricity as every atom is strongly bonded to others

doesn't conduct electricity as every atom is strongly bonded to others

Correct Answer:graphite,hexagonal rings of carbon atoms, arranged in layers

hexagonal rings of carbon atoms, arranged in layers

Correct Answer:carbon dioxide,made of simple molecules with low melting and boiling points

made of simple molecules with low melting and boiling points

Correct Answer:coal,a mixture of carbon-containing molecules

a mixture of carbon-containing molecules

Q5.
Match the key words to their definitions.
Correct Answer:simple molecular,distinct units made up of two or more atoms covalently bonded

distinct units made up of two or more atoms covalently bonded

Correct Answer:model,represent parts of the natural world that are too difficult to observe

represent parts of the natural world that are too difficult to observe

Correct Answer:intermolecular force,weak forces of attraction between molecules

weak forces of attraction between molecules

Correct Answer:giant covalent,large regular arrangement of atoms all joined by covalent bonds

large regular arrangement of atoms all joined by covalent bonds

Q6.
[a] covalent substances have [b] melting points as they're held together by strong covalent bonds. [c] covalent substances have [d] melting points as there are weak forces between molecules.
Correct answer: giant, high, simple, low
giant, low, simple, high
simple, high, giant, low
simple, low, giant, high