Module 2.2.2 - Bonding and Structure definitions Flashcards
What is an ionic bond?
The electrostatic attraction between oppositely charged (positively and negatively) ions
What is the octet rule?
The tendency to acquire a noble gas electron configuration (8 electrons in its outer shell)
What is covalent bonding?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What are lone pairs (of electrons)?
Pairs of electrons in the outer shell of an atom not involved in covalent bonding
What is a single covalent bond?
The sharing of one pair of electrons between two atoms
What are multiple (double/triple) covalent bonds?
A double/triple covalent bond is the sharing of two/three pairs of electrons between two atoms
What is dative covalent (coordinate) bonding?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms, where only one of the atoms supplies both of the electrons shared
What is metallic bonding?
The **strong electrostatic attraction ** of a lattice of cations (positive metal ions) to a ‘sea’ of delocalised electrons.
What does the giant ionic lattice result from?
The regular arrangement of oppositely charged ions strongly attracted in all directions
What do substances need in order to conduct electricity?
Mobile charge carrier such as delocalised electrons or mobile ions
What does ‘mobile’ mean
Free to move
What is average bond enthalpy?
Average bond enthalpy can be used as a measurement of covalent bond strength
What is the basis of electron pair repulsion theory?
- Electron pairs repel each other to get as far away as possible
- Lone pairs repel more strongly than bonding pairs
- Shape is determined by the number and type of electron pairs (bond pairs / lone pairs) around the central atom
What does a normal line in a 3D shape represent?
Shows a bond in the plane of paper
What does a bold wedge in a 3D shape represent?
Bond comes out from the plane of the paper towards you
What does a dashed line/dotted wedge in a 3D shape represent?
Bond going out from the plane of the paper away from you
What is a linear molecule?
- 2 bonded pairs, 0 lone pairs
- bond angle 180°
What is a trigonal planar molecule?
- 3 bonded pairs, 0 lone pairs
- bond angle of 120°
What is a tetrahedral molecule?
- 4 bonded pairs, 0 lone pairs
- bond angle of 109.5°
What is a octahedral molecule?
- 6 bonded pairs, 0 lone pairs
- bond angle of 90°
What is a pyramidal molecule?
- 3 bonded pairs, 1 lone pair
- bond angle of 107° (109.5°-2.5°)
What are the non-linear molecules?
- 2 bonded pairs, 1 lone pair
- bond angle of 117.5° (120°- 2.5°)
OR - 2 bonded pairs, 2 lone pairs
- bond angle of 104.5° (109.5°- 5°)
What is electronegativity?
The ability of an atom to attract the bonding electrons towards itself in a covalent bond
What are non-polar bonds?
The difference in electronegativity is 0, bonded electrons are equally distributed
When do non-polar bonds occur?
Where the bonding atoms are the same such as H-H and Cl-Cl
What are polar covalent bonds?
Where there is a medium to small difference in electronegativity between the bonded atoms
What happens between the bonded atoms in a polar covalent bond?
There is a permanent dipole across the bond due to the small difference in charge across the bond
What happens to the shared electrons in a polar covalent bond?
Bonding electrons are attracted closer to the more electronegative atom , electron cloud is more dense
What is the general trend for electronegativity in the periodic table?
Electronegativity increases towards the top right of the periodic table (halogens, excluding most noble gases)
The greater the difference in electronegativity between the bonded atoms…
the greater the permanent dipole and the more polar the covalent bond.
What do polar covalent bonds have in terms of charges?
Slight/Partial charges, represented with a dipole
Why do carbon and hydrogen not form a polar covalent bond?
There is a very small difference in electronegativity between C and H
Why are symmetrical molecules non-polar?
The dipoles cancel out between each polar bond, hence no net dipole across the molecule
When are asymmetrical molecules polar?
When they contain one or more polar bonds
How can you tell is a molecule is asymmetric?
- has lone pairs
- surrounding atoms are not all the same
Why are asymmetrical molecules polar?
The dipoles do not cancel out
What are intermolecular forces?
Attractive forces between molecules which are much weaker than ionic or covalent bonds
What structures have intermolecular forces?
Covalent structures
What are induced dipole-dipole interactions?
Very weak intermolecular forces between molecules
What are other names for induced dipole-dipole interactions?
- London forces
- Dispersion forces
Where do induced dipole-dipole interactions exist?
Between all molecules, whether polar or non-polar
How do induced dipole-dipole arise between molecules?
- At any moment there may be an uneven distribution of electrons in a molecule, due to electron movement/change in electron density
- This causes a temporary dipole/instantaneous dipole to occur
- The instantaneous/temporary dipole in one molecule causes an induced dipole in a neighbouring molecule
- The slightly positive charge of a dipole in one molecule attracts the slightly negative charge of a dipole in a neighbouring molecule, producing a induced dipole-dipole attraction
What are permanent dipole-dipole interactions?
Weak attractive forces between polar molecules
How do permanent dipole-dipole interactions occur?
- A molecule has bonds that are permanently polar as one atom is more electronegative than the other and is asymmetrical so the dipoles do not cancel each other out
- the slightly positive dipole of one molecule attracts the slightly negative dipole of a neighbouring molecule to produce the permanent dipole-dipole force of attraction between the molecules
What can both permanent dipole-dipole interactions and induced dipole-dipole interactions be referred as?
Van der Waals forces
What are hydrogen bonds?
A strong dipole-dipole attraction between molecules containing O-H, N-H or F-H bonds, the strongest type of intermolecular force of attraction
What does the hydrogen bond exist between?
- The slightly positive charge on the hydrogen in one molecule
- a lone pair on a highly electronegative atom (O, N, F) on another molecule
How do you draw a hydrogen bond? [3 marks]
- labelled atoms (with dipoles)
- lone pairs of electrons
- dotted line (hydrogen bond)
Why does water have anomalous properties of water?
Due to the hydrogen bonds between water molecules
Why is ice (solid H2O) less dense than liquid water?
- In the solid, H2O molecules are held further apart by the hydrogen bonds
- This gives the ice an open lattice structure
- The H2O molecules are fixed in their positions in the 3D ice crystal lattice by hydrogen bonds
Why does water have relatively high melting and boiling points?
- Water has higher than expected melting and boiling points
- Hydrogen bonds are relatively strong, therefore stronger than other intermolecular forces
- more energy is needed to break the hydrogen bonds
What does melting and boiling points depend on?
The structure and the strength of the bonds, which need to be overcome and broken
When does a substance have a high melting/boiling point?
The bonds broken are strong
What is the structure of substances with a high melting/boiling point?
Giant
When does a substance have a low melting or boiling point?
When the bonds broken are weak
What is the structure of substances with a low melting/boiling point?
Simple
When is there a sharp decrease in melting and boiling points across a period?
Between group 4 and 5
What does the decrease show across the period?
The change from giant structures to simple structures
What are the bonds that need to be broken in substances with a high melting or boiling point?
Strong bonds between the particles/atoms
What are the bonds that need to be broken in substances with a low melting or boiling point?
Weak intermolecular forces between molecules
What happens to the melting or boiling point across a period from group 1 to group 4?
Increase gradually
What are relative to the melting or boiling points across a period from group 5 to group 8?
They are comparatively low
