What holds atoms together, and how does the type of bonding explain a substance's shape and properties?
Ionic, covalent, dative and metallic bonding, electronegativity and bond polarity, the shapes of simple molecules and ions from electron-pair repulsion, and the intermolecular forces.
An Eduqas A-Level Chemistry C1.4 answer on ionic, covalent, dative and metallic bonding, electronegativity and polarity, molecular shapes from electron-pair repulsion, and intermolecular forces.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this topic is asking
Eduqas topic C1.4 covers the three main types of strong bonding (ionic, covalent and metallic), the dative covalent bond, electronegativity and polarity, the shapes of molecules and ions predicted by electron-pair repulsion, and the weaker intermolecular forces that govern physical properties. It links electronic structure to the behaviour of real substances.
The strong bonds
Electronegativity and polarity
Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond; it increases across a period and up a group, so fluorine is the most electronegative element. When two bonded atoms differ in electronegativity, the bonding pair is pulled toward the more electronegative atom, creating a polar bond with partial charges and .
Shapes of molecules and ions
The shape is set by the number of electron pairs around the central atom, which repel to be as far apart as possible. Lone pairs repel more strongly than bonding pairs, reducing bond angles by about each.
Intermolecular forces
Between molecules act three forces of increasing strength: van der Waals (temporary induced dipoles, present in all molecules and stronger with more electrons), permanent dipole-dipole (between polar molecules) and hydrogen bonding (when H is bonded to N, O or F and another molecule has a lone pair on N, O or F). These forces, not the covalent bonds, are broken on melting and boiling a molecular substance.
Examples in context
Example 1. Ice is less dense than water. Hydrogen bonds hold water molecules in an open, regular lattice in ice, spacing them further apart than in liquid water, so ice floats. This is why lakes freeze from the top down.
Example 2. Why simple molecular iodine is a solid but chlorine a gas. Both are non-polar diatomic molecules with only van der Waals forces, but iodine has many more electrons, so its induced-dipole forces are much stronger and more energy is needed to separate the molecules.
Try this
Q1. Describe the bonding in a metal and use it to explain why metals conduct electricity. [2 marks]
- Cue. Positive metal ions in a lattice surrounded by a sea of delocalised electrons; the delocalised electrons are free to move and carry charge through the metal.
Q2. State the shape and bond angle of the ion. [1 mark]
- Cue. Tetrahedral, (four bonding pairs, no lone pairs; one bond is dative).
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20184 marks(a) State the shape and bond angle of a molecule of boron trifluoride, , and of ammonia, . (b) Explain why the two shapes differ.Show worked answer →
(a) is trigonal planar with bond angles of (1). is pyramidal with bond angles of about (1).
(b) Boron in has three bonding pairs and no lone pairs, which repel equally to give (1). Nitrogen in has three bonding pairs and one lone pair; the lone pair repels more strongly than bonding pairs, pushing the bonds closer together to about (1).
Eduqas 20213 marksExplain why water () has a much higher boiling temperature than hydrogen sulfide (), even though sulfur is in the same group as oxygen and has a higher relative molecular mass.Show worked answer →
Water molecules form hydrogen bonds because hydrogen is bonded to highly electronegative oxygen, creating large and charges and an available lone pair on oxygen (1).
has only weaker dipole-dipole forces and van der Waals forces, because sulfur is not electronegative enough to form hydrogen bonds (1). The hydrogen bonds in water are stronger and need more energy to overcome, so water boils at a much higher temperature despite its lower molecular mass (1).
Related dot points
- The four types of crystalline solid (ionic, simple molecular, giant covalent and metallic), their structures, and how structure and bonding explain physical properties.
An Eduqas A-Level Chemistry C1.5 answer on ionic, simple molecular, giant covalent and metallic crystalline solids and how their structure and bonding explain melting point, hardness, solubility and conductivity.
- Periodicity of atomic radius, ionisation energy and melting temperature across Periods 2 and 3, the s, p and d blocks, and the trends explained by electronic structure and nuclear charge.
An Eduqas A-Level Chemistry C1.6 answer on periodicity across Periods 2 and 3: trends in atomic radius, ionisation energy and melting temperature, the s, p and d blocks, and their explanation from electronic structure.
- Subatomic particles and isotopes, relative atomic mass from mass spectra, the principles of time-of-flight mass spectrometry, and electron configuration in shells, sub-shells and orbitals including ionisation energy evidence.
An Eduqas A-Level Chemistry C1.2 answer on subatomic particles, isotopes, relative atomic mass from mass spectra, time-of-flight mass spectrometry and electron configuration with ionisation energy evidence.
- Writing formulae from ionic charges and oxidation states, constructing balanced chemical and ionic equations with state symbols, and using the language of chemistry consistently.
An Eduqas A-Level Chemistry C1.1 answer on writing formulae from ionic charges, constructing balanced full and ionic equations with state symbols, and the conventions of chemical language.
Sources & how we know this
- WJEC Eduqas GCE A Level Chemistry specification (from 2015) — WJEC Eduqas (2015)