Topic 2 - Bonding and Structure
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What is ionic bonding?
the strong electrostatic attraction between oppositely charged ions -metal atoms (become cations) give electrons to non-metal atoms (become anions)
What factors affect the strength of an ionic bond?
• ionic radius - charge
How does ionic radii affect the strength of an ionic bond?
as ionic radii increases, the strength of the bond decreases smaller ions = greater attraction
How does charge affect the strength of an ionic bond?
as charge increases, the strength of the bond increases higher charge = great attraction
How does an atom become a cation?
by loosing (giving away) electrons so that it becomes positively charged
How does an atom become an anion?
by gaining electrons so that it becomes negatively charged
What is the trend in ionic radii down a group and for a set of isoelectronic ions and why?
number of protons increases down the group/set of isoelectronic ions meaning that the electrons get pulled in more closely ∴ ionic radii decreases
What is the evidence for the existence of ions?
the migration of ions eg. using copper sulfate in a u-tube -blue Cu 2+ ions migrate towards cathode using potassium manganate crystals -purple MnO4 - ions (manganate ions) migrate towards positive ions
What is covalent bonding?
the strong electrostatic attraction between two nuclei and the shared pair of electrons between them -overlap of orbitals where there is a shared area of electron density
What is a sigma bond?
strongest type of covalent bond formed by the overlap of s/p orbitals or 2 p orbitals end-to-end
What is a pi bond?
weaker type of covalent bond formed by the overlap of p orbitals side-to-side -only exist when a sigma bond is present too
What is the relationship of bond strength and bond length in covalent bonds?
the larger the bond (greater the distance between the two nuclei), the weaker the bond
What is a dative covalent bond?
a covalent bond where more bonding electrons come from one atom in the bond than the other
Name some examples of molecules containing a dative bond
Al2Cl6 ammonium ion NH4 +
What is the linear shape of molecules?
2 bonding pairs of electrons and 0 long pairs of electrons • bond angle 180° eg. CO2 BeCl2
What is the trigonal planar shape of molecules?
3 bonding pairs of electrons and 0 long pairs of electrons • bond angle 120° eg. BCl3
What is the tetrahedral shape of molecules?
4 bonding pairs of electrons and 0 long pairs of electrons • bond angle 109.5° eg. CH4
What is the V-shaped shape of molecules?
2 bonding pairs of electrons and 2 long pairs of electrons • bond angle 104.5° eg. H2O
What is the pyramidal shape of molecules?
3 bonding pairs of electrons and 1 long pairs of electrons • bond angle 107.5° eg. NH3
What is the trigonal bipyramidal shape of molecules?
5 bonding pairs of electrons and 0 long pairs of electrons • bond angle 120° and 90° eg. PCl5
What is the octahedral shape of molecules?
6 bonding pairs of electrons and 0 long pairs of electrons • bond angle 90° eg. SF6
What is the shape of a simple molecule or ion is determined by?
the repulsion between the electron pairs that surround a central atom
Name an example of a linear molecule
CO2 BeCl2
Name an example of a trigonal planar molecule
BCl3