Topic 2: Bonding and Structure Flashcards
What is an ionic bond?
An electrostatic force of attraction between oppositely charged ions
What is a covalent bond?
An electrostatic force of attraction between two positive nuclei and the shared negative electrons between them
What is a metallic bond?
An electrostatic force of attraction between the positive metal ions and the negatively-charged sea of delocalised electrons
What is a lone pair?
(of electrons)
A pair of electrons not being used in covalent bonds
What is a dative covalent bond?
A covalent bond where both electrons in the ‘shared’ pair come from one of the atoms (which come from the lone pair in the atom!)
How are dative covalent bonds represented in the stick diagrams for covalent structures?
They are an arrow, from the atom from which the two electrons in the bond are from, to the other atom
Draw the Al2Cl6 molecule
(Should have two Al atoms and six Cl atoms, where the two Al atoms are not bonded to each other, but have two Cl atoms in common, and two Cl atoms each. The dative bonds are between the shared Cl atoms and one each of the Al atoms.)
Draw the NH4+ molecule
(Should have a central N atom, with three H atoms that are normal covalent bonds, and one H atom that is a dative covalent bond, where both electrons come from the N atom.)
Write the order of strength of repulsion between different kinds of electron pair.
- Lone pair - Lone pair
- Lone pair - Bonding pair
- Bonding pair - Bonding pair
How much more do double bonds repel than single bonds
None - they repel the same
How much more do lone pairs repel than a bonding pair
2.5 degrees more
2 electron pairs: 2 bond pairs around a central atom
Name: Linear
Bond angles: 180
3 electron pairs: 3 bond pairs around a central atom
Name: Trigonal Planar
Bond angles: 120
3 electron pairs: 2 bond pairs and 1 lone pair around a central atom
Name: Bent
Bond angle: 119
4 electron pairs: 4 bond pairs around a central atom
Name: Tetrahedral
Bond angles: 109.5
4 electron pairs: 3 bond pairs and 1 lone pair around a central atom
Name: Trigonal pyramidal
Bond angles: 107
4 electron pairs: 2 bond pairs and 2 lone pairs
Name: Angular
Bond angles: 104.5
5 electron pairs: 5 bond pairs around a central atom
Name: Trigonal bipyramidal
Bond angles: 120 and 90
5 electron pairs: 4 bond pairs and 1 lone pair around a central atom
Name: See-saw
Bond angles: 117.5 and 87.5
5 electron pairs: 3 bond pairs and 2 lone pair around a central atom
Name: T-shaped
Bond angles: 87.5
6 electron pairs: 6 bond pairs around a central atom
Name: Octahedral
Bond angles: 90
6 electron pairs: 5 bond pairs and 1 lone pair around a central atom
Name: Square pyramidal
Bond angles: slightly less than 90
6 electron pairs: 4 bond pairs and 2 lone pair around a central atom
Name: Square planar
Bond angles: 90 (lone pair are on opposite sides and effectively balance each other out)
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
What are the most electronegative elements?
(Top 4)
Flourine, oxygen, chlorine and nitrogen
Why are the most electronegative elements the most electronegative?
They have smaller atomic radius and higher nuclear charges
What is the trend in electronegativity across groups and periods
(And why!?)
- Electronegativity increases across the period because the nuclear charge increases.
- Electronegativity increases up the group because the atomic radius decreases.
What makes a covalent bond polarised?
A difference in the electronegativity of the atoms
What does it mean if a covalent bond is polar?
The electron density will be pulled towards the more electronegative atom, so each atom has a partial charge. The more electronegative atom will be ‘slightly negative’, while the other side is ‘slightly positive’ (denoted by delta- or delta+).
What characteristics of the two atoms in a covalent bond are needed for the bond to be non-polar?
They need to have the same or similar electronegativities (e.g in diatomic molecules)
What does dipole mean?
A difference in charge between the two atoms caused by a shift in the electron density in the bond.
What does overall dipole mean?
When there is a permenant charge across the moleucle because the polar bonds aren’t ‘balanced’.
What is a molecule called when the polar bonds in the molecule are uneven (so don’t balance out)
The molecule will be a polar molecule, and will have an overall permenant dipole.
How do you know if a molecule with polar bonds is a polar molecule or not?
Whether or not a molecule is polar or not depends on the symmetry of the molecule’s shape, and whether the forces will ‘balance’ out (think like vectors!!!)
