Easy summary for Chemical bonding a level chemistry

Easy summary for Chemical bonding a level chemistry cameroon gce revision

Learning outcomes
You should be able to: ■

■ describe diff erent types of bonding using ‘dot-andcross’ diagrams, including: – ionic bonding – covalent bonding – co-ordinate (dative covalent) bonding ■

■ explain the shapes of, and bond angles in, molecules by using the qualitative model of electron-pair repulsion (including lone pairs) using as simple examples: BF3 (trigonal), CO2 (linear), CH4 (tetrahedral), NH3 (pyramidal), H2 (non-linear), SF6 (octahedral) and PF5 (trigonal bipyramidal) ■

■ describe covalent bonding in terms of orbital overlap, giving and π bonds, including the concept of hybridisation to form sp, sp2 and sp3 orbitals ■

■ explain the shape of, and bond angles in, ethane and ethene, and use this knowledge to predict the shapes of, and bond angles in, similar molecules ■

■ explain the terms bond energy, bond length and bond polarity and use them to compare the reactivities of covalent bonds ■

■ describe intermolecular forces based on permanent and induced dipoles, hydrogen bonding and metallic bonding ■

■ describe, interpret and predict the eff ect of diff erent types of bonding on the physical properties of substances ■

■ deduce the type of bonding present from given information


Summary for chemical bonding
■ Ions are formed when atoms gain or lose electrons.

■ Ionic (electrovalent) bonding involves an attractive force between positively and negatively charged ions in an ionic lattice.

■ A covalent bond is formed when atoms share a pair of electrons.

■ When atoms form covalent or ionic bonds each atom or ion has a full outer electron shell of electrons. (Some covalent compounds may be electron deficient or have an ‘expanded octet’.)

■ Dot-and-cross diagrams can be drawn to show the arrangement of electrons in ionic and covalent compounds.

■ In dative covalent bonding one atom provides both electrons in the formation of the covalent bond.

 ■ The shapes and bond angles in molecules can be predicted using the idea that lone pairs of electrons repel other lone pairs more than bond pair electrons, and that bond pair to bond pair repulsion is least.

■ σ bonds (sigma bonds) are formed by end-on overlap of atomic orbitals, whereas π bonds (pi bonds) are formed by sideways overlap of p-type atomic orbitals.

■ Three types of relatively weak intermolecular forces are hydrogen bonding, permanent dipole–dipole forces and van der Waals’ forces.

■ Electronegativity differences can be used to predict the type of weak intermolecular forces between molecules.

■ Hydrogen bonding occurs between molecules that have a hydrogen atom covalently bonded to an atom of a very electronegative element (fluorine, oxygen or nitrogen).

■ The reactivities of covalent bonds can be explained in terms of bond energy, bond length and bond polarity.

■ Intermolecular forces are based on either permanent dipoles, as in CHCl3(l), or temporary induced dipoles (van der Waals’ forces), as in Br2(l).

■ Metallic bonding can be explained in terms of a lattice of positive ions surrounded by mobile electrons.

■ The physical properties of substances may be predicted from the type of bonding present.

■ Substances with ionic bonding have high melting and boiling points, whereas simple molecules with covalent bonding have low melting points.

■ The presence of hydrogen bonding in a molecule influences its melting point and boiling point.