Covalent bonding (Edexcel IGCSE Chemistry (Modular): Unit 2): Flashcards

Complete the table to show the number of shared pairs in each bond type.

True.

Oxygen forms two covalent bonds in H₂O, one with each hydrogen atom. Each bond consists of one shared pair of electrons.

Nitrogen forms a triple bond in N₂, sharing three pairs of electrons. This gives each nitrogen atom a full outer shell of eight electrons.

False.

Dot and cross diagrams show both bonding electrons and non-bonding electrons (lone pairs) on the outer shells of each atom.

Intermolecular forces are the weak forces of attraction that act between neighbouring molecules in a simple molecular structure.

False.

Simple molecular structures have low melting and boiling points because there are only weak intermolecular forces between the molecules, which need little energy to overcome.

Larger molecules have more electrons, so there are more intermolecular forces of attraction between molecules. More energy is needed to overcome these forces, giving larger molecules higher melting and boiling points.

Buckminsterfullerene contains 60 carbon atoms arranged into 20 hexagons and 12 pentagons, forming a hollow sphere.

Simple molecular structures cannot conduct electricity because they have no free ions or electrons to move and carry the charge. This applies even when the substance is melted.

False.

C₆₀ fullerene is a simple molecular structure. It has weak intermolecular forces between the buckyballs, giving it a relatively low melting point.

A fullerene is a carbon allotrope made up of molecules that form hollow tubes or spheres.

1. Drug delivery — fullerenes can trap molecules inside them and carry them to specific targets in the body.

2. Catalysis — their huge surface area makes them useful for trapping catalyst molecules, making reactions more efficient.

Complete the table showing the properties of simple molecular structures.

A giant covalent structure is a solid containing a huge number of non-metal atoms joined by strong covalent bonds in a regular lattice. Examples include diamond and graphite.

False.

Giant covalent structures have high melting points because the covalent bonds between atoms are very strong and need a large amount of energy to break.

Giant covalent structures have high melting points because they contain many strong covalent bonds between atoms. These bonds require a large amount of energy to break.

In diamond, each carbon atom forms covalent bonds with four other carbon atoms, giving each atom a full outer shell.

An allotrope is a different physical form of the same element, in which the atoms are arranged or bonded differently. Diamond and graphite are both allotropes of carbon.

Diamond is hard because each carbon atom is covalently bonded to four other carbon atoms in a strong, rigid three-dimensional structure. There are no layers that can slide, and all the covalent bonds are very strong.

True.

In graphite, each carbon atom forms only three bonds, leaving one electron per atom delocalised. These free electrons can move and carry charge, allowing graphite to conduct electricity.

In graphite, carbon atoms form layers of hexagons. There are only weak forces between the layers, so the layers can slide over each other easily, making graphite slippery.

Complete the table to compare diamond and graphite.

In graphite, carbon atoms form layers held together by only weak forces. These layers can slide over each other easily, which is why graphite is a good lubricant.