Shapes of molecules

when drawing dot cross diagrams, which elements must have 8 in their outer shell

C, N, O, F
the other can have more or less

when drawing a dot cross diagram of a charged molecule, how do you go about it

alter the central atom in the diagram in relation to charge, then carry on as normal

e.g. CO3^2-

draw carbon atom to have 6 electrons in outer shell (2- charge) rather than regular 4 in outer shell

then draw as normal

define a metallic bond

strong electrostatic force of attraction between positive metal ions and negative delocalised electrons

what are van den waal forces and how do they occur

• present between all molecules

• electrons are constantly moving, therefore uneven electron distribution

• causes a temporary dipole within a molecule which induces a dipole in neighbouring molecule

• δ+ side of one molecule attracts δ- side of other molecule

how is a dative bond formed between X and Y

• lone pair / both electrons on X is donated to Y

when drawing a diagram to show hydrogen bonding between 2 molecules, what are the key marking points

e.g. ammonia

1. lone pair on each N

2. partial charges on each molecule / atom

3. H bond from lone pair on N to Hδ+ on other NH₃ molecule

what increases the strength of van den waals and why

• the bigger the molecule, the stronger the VDW forces

• more electrons

list the three types of forces between molecules in order from weakest to strongest

1. van der waals

2. permanent dipole dipole attraction

3. hydrogen bonding

when does permanent dipole dipole attraction occur

• between polar molecules

why might a molecule have polar bonds but not permanent dipole dipole attraction

e.g. CCL₄

tetrahedral symmetrical structure

polar bonds cancel out

therefore molecule is not polar

so no permanent dipole dipole attraction between molecules

when can hydrogen bonding occur

• when H atom is bonded to F, O, or N

what is hydrogen bonding

• strong attraction from lone pair of electrons on N/O/F of one molecule to the exposed H nucleus of another molecule

why is a Cl₂ molecule non polar

• both Cl atoms have the same electronegativity so the bonding electron are shared equally between the two atoms

do lone pairs of electrons repel more or less than bonding pairs

more

what is the shape and bond angle in a molecule with:

• 2 electron pairs

• 2 bonding pairs

• 0 lone pairs

linear

180 degrees

what is the shape and bond angle in a molecule with:

• 3 electron pairs in total

• 3 bonding pairs

• 0 lone pairs

trigonal planar

120 degrees

what is the shape and bond angle in a molecule with:

• 3 electron pairs in total

• 2 bonding pairs

• 1 lone pair

bent V shape

118 degrees

what is the shape and bond angle in a molecule with:

• 4 electron pairs in total

• 4 bonding pairs

• 0 lone pairs

tetrahedral

109.5 degrees

what is the shape and bond angle in a molecule with:

• 4 electron pairs in total

• 3 bonding pairs

• 1 lone pair

trigonal pyramidal

107 degrees

what is the shape and bond angle in a molecule with:

• 4 electron pairs in total

• 2 bonding pairs

• 2 lone pairs

bent v shape

104.5 degrees

what is the shape and bond angles in a molecule with:

• 5 electron pairs in total

• 5 bonding pairs

• 0 lone pairs

trigonal bipyramidal

90 degrees

120 degrees

what is the shape and bond angles in a molecule with:

• 5 electron pairs in total

• 4 bonding pairs

• 1 lone pair

trigonal pyramidal

119 degrees

89 degrees

what is the shape and bond angle in a molecule with:

• 5 electron pairs in total

• 3 bonding pairs

• 2 lone pairs

trigonal planar or T shape

120 degrees or 89 degrees

what is the shape and bond angle in a molecule with:

• 6 electron pairs in total

• 6 bonding pairs

• 0 lone pairs

octahedral

90 degrees

what is the shape and bond angle in a molecule with:

• 6 electron pairs in total

• 5 bonding pairs

• 1 lone pair

square pyramid

89 degrees

what is the shape and bond angle in a molecule with:

• 6 electron pairs in total

• 4 bonding pairs

• 2 lone pairs

square planar

90 degrees

define electronegativity

• power of an atom to attract the pair of electrons in a covalent bond towards itself

what is the most electronegative element in the periodic table

what does this mean?

fluorine

• best at attracting electron density towards itself when covalently bonded to another atom

how do changes in nuclear charge affect electronegativity

• increased nuclear charge = increased electronegativity

• Attraction between positively charged protons in nucleus and negatively charged electrons in energy levels of atom

• increase in number of protons→ increase in nuclear attraction for electrons in the outer shells