Covalent Bonding (Edexcel IGCSE Science (Double Award): Chemistry): Flashcards
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Define covalent bond.
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Define covalent bond.
A covalent bond is a bond formed between atoms by the sharing of a pair of electrons.
In a covalent bond, each atom usually provides .......... of the electrons in the shared pair.
In a covalent bond, each atom usually provides one of the electrons in the shared pair.
True or False?
Covalent bonds form between non-metal atoms only.
True.
Covalent bonds form when non-metal atoms share pairs of electrons to achieve a full outer shell.
Why do non-metal atoms form covalent bonds?
Non-metal atoms form covalent bonds to achieve a full outer shell of electrons, which gives each atom a more stable electron configuration similar to a noble gas.
Define bonding electrons.
Bonding electrons are shared electrons that form a covalent bond, always occurring in pairs.
Electrons in the outer shell that are not involved in a covalent bond are called .......... electrons.
Electrons in the outer shell that are not involved in a covalent bond are called non-bonding electrons.
True or False?
In a covalent bond, electrons are transferred from one atom to the other.
False.
In a covalent bond electrons are shared between atoms, not transferred. Electron transfer occurs in ionic bonding.
What holds the atoms together in a covalent bond?
The atoms are held together by the strong electrostatic attraction between the positively charged nuclei of both atoms and the negatively charged shared pair of electrons.
Define non-bonding electrons.
Non-bonding electrons are outer-shell electrons that are not involved in any covalent bond and do not form part of a shared pair.
True or False?
Covalent bonds are weak and easily broken at room temperature.
False.
Covalent bonds between atoms are very strong and require significant energy to break.
Define dot and cross diagram.
A dot and cross diagram is a representation of a molecule that shows the arrangement and sharing of outer-shell electrons between bonded atoms.
What does each covalent bond represent in a dot and cross diagram?
Each covalent bond represents one shared pair of electrons, with one electron contributed by each of the two bonded atoms.
In a dot and cross diagram, dots and crosses are used to show electrons from .......... different atoms so their origins can be distinguished.
In a dot and cross diagram, dots and crosses are used to show electrons from two different atoms so their origins can be distinguished.
True or False?
A nitrogen molecule, N2, contains a triple covalent bond.
True.
Each nitrogen atom has five outer electrons and needs three more to fill its shell, so the two nitrogen atoms share three pairs of electrons forming a triple bond.
How many covalent bonds does each carbon atom form in methane, CH4?
Each carbon atom forms four covalent bonds in methane, one with each hydrogen atom, giving carbon a full outer shell of eight electrons.
In a molecule of oxygen, O2, the two atoms share .......... pairs of electrons, forming a double bond.
In a molecule of oxygen, O2, the two atoms share two pairs of electrons, forming a double bond.
True or False?
In ammonia, NH3, the nitrogen atom has one non-bonding pair of electrons.
True.
Nitrogen forms three covalent bonds with the three hydrogen atoms, leaving one non-bonding pair of outer-shell electrons.
How many shared pairs of electrons are shown in the dot and cross diagram for CO2?
The dot and cross diagram for CO2 shows four shared pairs of electrons in total: two shared pairs (a double bond) between carbon and each oxygen atom.
Define simple molecule.
A simple molecule is a small covalently bonded molecule consisting of a fixed small number of atoms joined by shared electron pairs.
In a dot and cross diagram for H2O, how many non-bonding pairs of electrons does the oxygen atom have?
The oxygen atom in H2O has two non-bonding pairs of electrons: oxygen forms two covalent bonds with the hydrogen atoms, leaving two pairs unused.
Define simple molecular structure.
A simple molecular structure is one in which small covalently bonded molecules are held together by weak intermolecular forces, giving low melting and boiling points.
Why do simple molecular structures have low melting and boiling points?
Simple molecular structures have low melting and boiling points because the intermolecular forces between molecules are weak and require little energy to overcome.
True or False?
When a simple molecular substance melts, its covalent bonds are broken.
False.
When a simple molecular substance melts it is the weak intermolecular forces between molecules that are overcome, not the strong covalent bonds within the molecules.
Simple molecular structures generally .......... conduct electricity because they have no free .......... or electrons.
Simple molecular structures generally do not conduct electricity because they have no free ions or electrons.
How does increasing relative molecular mass affect the melting point of a simple molecular substance?
As relative molecular mass increases, the melting point generally increases because larger molecules have stronger intermolecular forces that require more energy to overcome.
Define intermolecular forces.
Intermolecular forces are weak forces of attraction that act between neighbouring molecules in a simple molecular substance.
True or False?
C60 fullerene can conduct electricity because it contains delocalised electrons.
False.
C60 fullerene has a simple molecular structure. Although electrons exist within each molecule, they cannot move between the separate molecules, so C60 cannot conduct electricity.
Buckminsterfullerene consists of .......... carbon atoms arranged in hexagons and pentagons to form a hollow .......... shape.
Buckminsterfullerene consists of 60 carbon atoms arranged in hexagons and pentagons to form a hollow sphere shape.
Why are fullerenes useful for drug delivery?
Fullerenes can trap other molecules inside their hollow sphere or tube structure, allowing them to carry and deliver drug molecules to specific targets in the body.
True or False?
Most simple molecular substances are gases or liquids at room temperature.
True.
The weak intermolecular forces between simple molecules require little energy to overcome, so most exist as gases or liquids under normal conditions.
Define giant covalent structure.
A giant covalent structure is a lattice of a very large number of non-metal atoms all joined by strong covalent bonds throughout the structure.
Why do giant covalent structures have very high melting points?
Giant covalent structures have very high melting points because they contain many strong covalent bonds throughout the lattice that require a large amount of energy to break.
In diamond, each carbon atom is covalently bonded to .......... other carbon atoms in a tetrahedral arrangement.
In diamond, each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement.
True or False?
Diamond can conduct electricity.
False.
Diamond cannot conduct electricity because all four outer electrons of each carbon atom are used in covalent bonds, leaving no free or delocalised electrons to carry charge.
Why is diamond extremely hard?
Diamond is extremely hard because each carbon atom is bonded to four others by strong covalent bonds in all directions, making the structure rigid and resistant to scratching.
Define allotropes.
Allotropes are different structural forms of the same element in the same physical state, such as diamond and graphite which are both forms of carbon.
In graphite, each carbon atom bonds to .......... others, forming layers of hexagons with one .......... electron per carbon atom.
In graphite, each carbon atom bonds to three others, forming layers of hexagons with one delocalised electron per carbon atom.
True or False?
Graphite can conduct electricity because it has delocalised electrons.
True.
Each carbon atom in graphite forms only three bonds, leaving one electron per atom delocalised and free to move through the layers and carry charge.
Why is graphite soft and slippery?
Graphite is soft and slippery because its carbon atoms are arranged in layers held together by only weak forces, allowing the layers to slide over each other easily.
True or False?
Diamond and graphite have different melting points because one is a giant covalent structure and the other is not.
False.
Both diamond and graphite are giant covalent structures with high melting points. Their other properties differ because of the different bonding arrangements within each structure.
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