2.5 Simple Molecules & Covalent Bonds (Cambridge (CIE) O Level Chemistry): Flashcards
Exam code: 5070
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- FrontCovalent Bonds
Define a covalent bond.
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Define a covalent bond.
A covalent bond is formed when a pair of electrons is shared between two atoms, leading to noble gas electronic configurations for both atoms.
True or False?
Covalent bonds form only between non-metal atoms.
True.
Covalent bonds form only between non-metal atoms. If a metal atom and a non-metal atom react, an ionic bond is formed instead.
In a covalent bond, each shared pair of electrons forms ______ bond. A double bond therefore involves ______ shared pairs of electrons.
In a covalent bond, each shared pair of electrons forms one bond. A double bond therefore involves two shared pairs of electrons.
What do atoms achieve by sharing electrons in a covalent bond?
By sharing electrons, both atoms achieve a noble gas electronic configuration — a full outer shell of electrons. This is a more stable arrangement.
True or False?
The term "relative formula mass" applies to all compounds, including covalent molecules such as water.
False.
Relative formula mass is used for ionic compounds. For covalent compounds (which form discrete molecules), the correct term is relative molecular mass.
In a nitrogen molecule (N2), the two atoms share ______ pairs of electrons, forming a ______ bond.
In a nitrogen molecule (N2), the two atoms share three pairs of electrons, forming a triple bond.
How many covalent bonds does a carbon atom form in methane (CH4), and why?
A carbon atom forms 4 covalent bonds in methane, one with each hydrogen atom. This gives carbon a full outer shell of 8 electrons, achieving a noble gas electronic configuration.
Why do simple molecular compounds have low melting and boiling points?
Simple molecular compounds have low melting and boiling points because only weak intermolecular forces act between the molecules. Little energy is needed to overcome these forces, so the compound is often a liquid or gas at room temperature.
True or False?
The low boiling point of methane (CH4) is due to its weak covalent bonds.
False.
The covalent bonds within each methane molecule are strong. The low boiling point is due to the weak intermolecular forces acting between the molecules, which require little energy to overcome.
Simple molecular compounds cannot conduct electricity because they contain no ______ and have no ______ electrons.
Simple molecular compounds cannot conduct electricity because they contain no ions and have no mobile/delocalised electrons.
True or False?
As the size of molecules in a homologous series increases, the boiling point generally increases.
True.
As molecules increase in size, the intermolecular forces between them become stronger. More energy is needed to overcome these forces, so the boiling point increases.
In simple molecular compounds, the ______ bonds within molecules are strong, but the ______ forces between molecules are weak.
In simple molecular compounds, the covalent bonds within molecules are strong, but the intermolecular forces between molecules are weak.
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