shapes of molecules

why does silicon have the highest melting point in period 3?

has many covalent bonds

which need a lot of energy to be broken

why does argon have the highest first ionisation energy in period 3?

largest number of protons

same number of shells

why is there 3 bonding pairs and 2 lone pairs in ClF3?

Cl has 7 electrons

F 3×1=3

7+3=10

10/2=5 electron density

3 bond pairs bc of F

5-3=2 lone pairs

explain shape of CCl2

3 electron density

2 bond pairs bc of Cl2

3-2=1 lone pair

bent shape with chlorines connected to carbon diagonally

explain why there can be a dative covalent bond

when the electron pair on the ion is donated to the central atom

explain shape of TlBr5 (2- charge) ion

Tl has 3 valence electrons

-2 charge adds 2 electrons so electron density is 5

5 bonding pairs bc of Br5

5-5=0 lone pairs

shape is trigonal bipyramidal

explain why there are linear shapes

because the two bond pairs of electrons repel equally to be as far apart as possible

explain why there is 1 lone pair in TlBr3(2-)

then say the shape and bond angle

Tl 3 valence electrons

2- charge adds 2 so 5 electrons

5+3=8

8/2=4 electron density

3 bond pairs bc of Br3

4-3=1 lone pair

shape is trigonal pyramidal

bond angle is 107.

explain, in terms of electronegativity, why the boiling point of H2S2 is lower than H2O2

.electronegativity of S is lower than O

.No hydrogen bonding between H2S2 molecules (only Van der Waals)

explain why CF4 has a bond angle of 109.5

.around carbon there are 4 bonding pairs of electrons and no lone pairs

.therefore, these repel equally and spread as far apart as possible.

what is electron pair repulsion theory?

electron pairs repel as far as possible

lone pairs repel more than bond pairs