Chem Chapt 2: Chemical Bonding

Define covalent bonds

It is the electrostatic forces of attraction between shared electrons and the positively charged nuclei formed between non-metals when they share their electrons through the overlap of orbitals

Outline the 2 types of orbital overlap

Head on overlap between s or p-orbitals will form a sigma bonds whereas side on overlap between s or p-orbitals will form a pi bond

Define dative bond

It occurs when the donor atom provides two electrons from a lone pair to an acceptor atom that contains a empty valence orbital

Outline how electronegative affects the sharing of electrons

It results in bonding electrons being unequally shared between the atoms whereby electrons are more strongly attracted to the more electronegative atom. The bigger the difference in electronegativity, the larger the dipole moment

Outline how bond order affects bond strength with the C-C and C=C example

The bond order of C=C is higher and hence it has a higher bond energy and the number of bonding electrons in the inter-nuclei region is higher than that in C-C

Outline how the effectiveness of bond overlap affect bond strength with the example of C-Cl and C-Br

C-Cl has a higher bond energy as the atomic orbital size of Cl is smaller than that or Br, hence the valence orbital used in bonding is less diffused than Br and allowing for more effective orbital overlap which confers higher bond energy

Outline how bond polarity affects bond strength with the example of C=O and N2 (This factor is only crucial if there is comparable bond order and orbital overlap effectiveness)

In a polar bond, there are additional attractive forces between the partial positive and partial negative region that strengthens the covalent bond, hence the more polar the bond, the larger the bond energy

Define bond length and how it affects bond strength

Bond length is defined as the average distance between the nuclei of two atoms, the shorter the bond length, the larger the bond strength

Outline which elements can expand octet configuration and why

Any element from period 3 onwards can expand octet configuration as they have energetically accessible d-orbitals, regardless of whether they have electrons occupying them

Outline which elements+molecules can exhibit odd number of electrons

Only group 2 and 13 molecules can have less than 8 electrons around central atom, or radicals

For dot and cross diagrams of covalent structures, outline which structures electrons are shared between

Electrons are shared between the most electronegative cation and the most electronegative anion

For dot and cross diagrams of ionic structures, what is a feature that differentiates it from covalent ones

The cation will have not have valence electrons

Outline what the Valence Shell Electron Pair Repulsion theory states (VSEPR)

It states that electron pairs, including bond pairs and lone pairs, are arranged as far apart as possible around a central atom to minimise inter-electronic repulsion. It also states that lone pair-lone pair repulsion>bond pair-lone pair repulsion>bond pair-bond pair repulsion.

Outline the shape and bond angle for 2 bond pairs and 3 bond pairs (all 0 lone pairs)

Linear, 180 and trigonal planar, 120

Outline all the shape and bond angles for 4 bond pairs

4 bond 0 lone is tetrahedral, 109.5. 3 bond 1 lone is trigonal pyramidal, 107. 2bond 2 lone is bent, 104.5

Outline the shape and bond angle for 5 bond and 6 bond pairs (all 0 lone pairs)

Trigonal bipyramidal, 120 along the equatorial plate and 90 along the axial. octahedral, 90

Outline the IMF between elements

They have idid between their atoms

Outline the factors that affect strength of idid

As the number of electrons increases, the electron cloud is bigger and more polarisable and idid is stronger. When molecules are branched and are more spherical, there is less surface area in contact with the other molecules, leading to weaker idid

Outline what affects the strength of pdpd

The more larger the difference in electronegativity between two atoms, the more polar a bond is and the larger a dipole moment, leading to stronger pdpd

Define hydrogen bonds

They are electrostatic forces of attraction between the partial positive hydrogen atom that is directly bonded to a very electronegative F, O, or N and a lone pair of another F, O, or N atom

Outline the bonding within a diamond and a silicon molecule

In a diamond molecules, each carbon atom is tetrahedrally bonded to 4 other carbon atoms by strong covalent bonds to form a giant 3d network. In silicon molecules, each silicon atom to covalently bonded to 4 oxygen atoms and each oxygen atom is bonded to 2 silicon atom

Outline the properties of silicon and diamond(Electrical conductor, solubility & toughness)

They are both non-conductors of electricity as all electrons are localised in covalent bonds and are not mobile. They are insoluble in both water and non-polar solvents no favourable solute-solvent interactions can be formed to break down the strong covalent bonds. They are hard and strong as atoms are held closely together by strong covalent bonds in a giant molecular structure, making them suitable as abrasives

Outline the bonding within graphite

Each carbon atom is held together by 3 other carbon atoms by covalent bonds to form extensive layers of hexagonal rings, whereby adjacent layers are held together by weak idid interactions

Outline the physical properties of graphite (electrical conductivity & toughness)

They are good conductors of electricity as one of the electron of carbon atom is not involved in bonding and can hence be delocalised to act as mobile charge carriers. They are also soft and slippery as when a force is applied, adjacent layers that are held by weak idid bonds can slide across each other easily

Define ionic bonding and state the formula for lattice energy

It is the strong electrostatic forces of attraction between oppositely charged ions in a giant ionic lattice structure. LE is given by (charge of cation multiplied by charge of anion)/anionic radius+cationic radius

Define LE

It is the energy released when 1 mole of solid ionic compound is formed from its constitutional gaseous ions

How are ions arranged in a ionic structure and outline the physical properties of ionic compounds(electrical conductivity, strength and solubility)

Oppositely charged ions are arranged in a fixed, orderly manner in a giant ionic lattice structure. They are non-conductors of electricity in solid states but they are conductors in the molten and aqueous state. They are strong and hard, but brittle, this is because when a force is applied, the layers of oppositely charged ions will slide and ions of the same charge would come together and repel each other. They are also only soluble in polar solvents as they form favourable ion-dipole interactions that will release sufficient energy to overcome the strong electrostatic forces of attraction

Suggest why there might be appearance of covalent character in ionic compounds

The larger the charge density of the cation and the greater its polarising power, and the larger the anion, the more polarisable it is and the more the appearance of covalent character.

Explain an alternative reason for covalent character in ionic compounds

As the electronegativity difference between the cation and anion decreases, the more the covalent character present in ionic compound

Explain how ionic character appears in covalent compounds

The larger the electronegativity difference between cation and anion, the larger the ionic character

Define metallic bonds and state formula for metallic bond strength

It is defined as the strong electrostatic forces of attraction between metal cations and sea of delocalised electrons in a giant metallic structure. metallic bond strength is given by charge of cation over cationic radii

Outline the physical properties of metals(electrical and heat conductivity, ductile and alloy formation)

They are good conductors of heat and electricity as they have a sea of mobile electrons that can conduct them easily, they are malleable and ductile as the layers of cations can slide across each other without repulsion when a force is applied due to the sea of delocalised electrons. Alloy formation is also favoured as they have a presence of cations of different sizes inhibits sliding of layers and increases tensile strength of alloys