Unit 1.4 - Bonding Flashcards
Ionic bond
Electrostatic attractions between oppositely charged ions.
Which elements form electrovalent compounds?
Group 1 and 2 with group 6 and 7.
1) What influences the formation of an ionic compound for a cation?
2) What influences the formation of an ionic compound for an anion?
1) Ionisation energy
2) Electron affinity
State 3 conditions that favour ionic bonding.
Low ionisation energy to form cations, highly exothermic formation if anions and attainment of a noble gas electron configuration in the ion.
Why are ionic bonds strong?
Energy released by the oppositely charged ions coming together to form a crystal lattice held by electrostatic forces.
Describe the relationship between the charge and force of an ion.
Larger charges on the ions, the bigger the attractive forces and the energy released.
State the order of shells.
1s2 2s2 2p6 3s2 3p6 4s2 3d10
When do repulsive forces exist in ionic crystals?
Repulsions between ions of the same charge, between inner shells of electrons in ions and between positively charged nuclei.
Inter-atomic distance - ionic and covalent
Balance between attractive and repulsive forces determines how closely cations and anions approach each other.
1) Why do group 1 element form ions most readily?
2) Why does ionisation energy occur more readily down a group?
1) Lowest effective nuclear charge.
2) Increase electron shielding which results in a decrease of the effective nuclear charge.
Describe relationship between electron affinity and its effect on the nucleus.
Electron affinities (energy released) becomes more exothermic across a period because the incoming electron is attracted more strongly by the increasingly positive charge on the nucleus.
Describe relationship between electron affinity and stability.
More exothermic (negative) electron affinity, more stable the anion that is formed.
State the name of the bond when there is a sharing of:
1) 2 electrons
2) 4 electrons
3) 6 electrons
1) Single bond
2) Double bond
3) Triple bond
What is covalent bonding?
Sharing of a pair of electrons with opposite spins between 2 atoms.
When do repulsive forces exist in covalent molecules?
Repulsions between inner shells of electrons on each atom, between those shells and charge cloud of the bond and between the positive charges on the nuclei.
What is the force of attraction in covalent bonding?
Directional
Covalent bond
Attraction between the nuclei and the shared pair of electrons.
What is another name for a coordinate bond?
Dative covalent bond.
How are aluminium chloride dimers formed?
Molecules dimerise together and monomers are held together by coordinate bonding.
1) When are coordinate bonds formed?
2) What is used to represent a coordinate bond?
1) Compounds containing unshared pairs of electrons (lone pairs).
2) Arrow - drawn from donor of electron pair to the acceptor.
Coordinate bond
Type of covalent bond, formed when one atom supplies the shared pair of electrons for the bond.
Electronegativity
Ability of an atom to attract shared pair of electrons in a covalent bond towards itself when combined with different atoms in a compound.
How does electronegativity vary:
1) Across a period?
2) Down a group?
1) Increases - atoms similar size, nuclear charge increases . Higher value, more attraction for bonding.
2) Decreases - atoms larger, more electron shielding.
Name the 4 most electronegative elements.
Fluorine, oxygen, nitrogen and chlorine. - alkalis have high values.
Polar covalent bond
Unequal distribution of bonding electron pair due to a difference in the electronegativity.
Polarisation
Unequal sharing of electrons and said to be polar.
Dipole
Separation of a charge in a molecule.
1) What forms electronegativity?
2) Describe the relationship between polarity and electronegativity.
3) What type of molecule would you fins non-polar covalent bonding?
1) Relative attraction of the nuclei for the bonding of electrons in a covalent bond.
2) Bigger difference in electronegativity, more polar the bond.
3) Diatomic elements.
What would a large difference in electronegativity lead to in ionic bonds?
Formation of a pure ionic bond and spherical ions.
What would the electron density cloud look like when atoms are the same?
Electron density cloud would be symmetrical.
Generally, when is ionic bonding favoured over covalent bonding? (3)
1) Atom from which the ion is derived is large for a cation and small for an anion - ionisation energy decreases, electron gain harder.
2) Formal charge on ion is small - more difficult no. electrons involved increase.
3) Electronic structure of ion corresponds to closed shell structure, especially noble gas configuration - stable which resistant to removal or addition of electrons.
Intramolecular bonds
Bonds between atoms within a molecule. They’re strong C-Cl.
Intermolecular forces
Forces of attraction between molecules (dipole-dipole). Easily broken to let molecules move independently so have low melting point and are usually gas/liquid at room temperature.
1) What influences physical properties?
2) What influences chemical properties?
1) Forces between molecules.
2) Forces within molecules.
What are dipole-dipole interactions?
Polar - any partial positive charge will be next to a negative partial charge.
What are induced dipole-dipole reactions?
Non polar molecules - electrons in continual motion therefore electron cloud will not be symmetrical at any given point. Resulting in a temporary dipole.
Describe the relationship between the size of a molecule and induced dipole attraction.
As size increases, number of electrons increases, causing induced dipole-induced dipole attraction to be stronger.
Using induced dipole-induced dipole knowledge, explain why the elements at top of group 7 are gaseous.
As you go down group 7 the electron cloud gets larger, Van Der Wall’s forces get stronger, causing boiling points to increase.
What increases Van Der Wall’s forces?
Increase in relative molecular mass.
Why do branched hydrocarbons have lower boiling points than unbranched hydrocarbons?
Unbranched have more points of contact so more Van Der Wall’s forces.
1) What is hydrogen bonding?
2) Is it stronger than Van Der Wall’s forces?
1) Attraction between the exposed proton of the hydrogen atom and the lone pair of electrons on the electronegative element of a neighbouring molecule.
2) Yes
What is required for hydrogen bonding?
Hydrogen atom attached to a highly electronegative atom (N,O,F), unshared pair of electrons on the electronegative atom.
Order the bonds from strongest to weakest.
Covalent bonds > hydrogen bonds > Van Der Wall’s forces
Why do bonds get as far away from each other as possible?
Electron pairs have negative charge so they repel and spread out.
VSEPR
Valence Shell Electron Pair Repulsion Theory.
State the 3 main points of VESPR theory.
1) Between each valence electron pair is a force of repulsion which forces orbitals as far apart as possible.
2) Since lone pairs are closer to the nucleus than bonding pairs they will exercise a greater force of repulsion.
3) A multiple bond can be considered as equivalent to one pair of electrons.
State the order of repulsion.
lone pair-lone pair > lone pair-bond pair > bond pair-bond pair
State the bond angle, example and bond/lone pairs in the following:
1) Linear
2) Trigonal Planar
3) Tetrahedral
4) Tetrahedral bent
1) 180°, 2bp
2) 120°, 3bp - BF3
3) 109.5°, 4bp - CH4, NH4 +
4) 104.5°, 2Lp, 2bp - H2O
State the bond angle, example and bond/lone pairs in the following:
1) Pyramidal
2) Trigonal bipyramidal
3) Octahedral
1) 106.7°, 1Lp, 3bp - NH3
2) 120°, 90°, 5bp - PCl5
3) 90°, 6bp - SF6
