Unit 3- Bonding

Question 1

Ionic bonding

Answer 1

• electrostatic attraction between oppositely charged ions
• when electrons transfer from one atom to another they cause ions to form that are attracted to each other and form bonds
• usually a metal (receiver) and non-metal (donor)
• large structures hold ions in strong lattice structure with high boiling points
• will conduct electricity when dissolved in water/molten
• dissolve as slight negative dipole in water molecules pull them apart
• e.g SO4 2-, OH-, NO3 -, CO3 2-, NH4+

Question 2

Covalent Bonding

Answer 2

• Overlap of electron orbitals as nuclei attract electrons from other atoms cause two atoms to share electrons
• shape of molecule is changed
• Bonds are strong between atoms, in small structures IMF is often very weak.
• can have single double or triple, which can contain multiple pairs of electrons
• carry no charge, do not dissolve
• simple structures have low boiling points
• macromolecular is stronger and has high boiling points

Question 3

Dative bonding

Answer 3

A covalent bond where one atom donates both electrons in a pair. Shown as an arrow pointing from the donor to the other atom

Question 4

Metallic Bonding

Answer 4

• positive metal ions surrounded by de-localised electrons holding them in lattice structures
• alows metal ions to move around within the sea of electrons, and allows formation of metal alloys
• delocalised electrons conduct heat/electricity well
• have high melting/boiling points due to strong electrostatic attraction, more electrons/ greater positive charge means more attraction

Question 5

Van Der Waals IMF

Answer 5

• hold together any non-polar simple molecules
• caused by temporary uneven distribution of electrons within a sysmetrical molecules orbitals inducing an opposite distribution in nearby molecules, creating slight electrostatic attraction
• strength of the induced temporary dipole is larger with greater size/more electrons

Question 6

Electronegativity

Answer 6

• an atoms ability to attract bonding electrons
• decreases as you go down a group, or left along a period
• atomic radius decreases along periods, increasing electronegativity
• shielding increases down a group, decreasing electronegativity

Question 7

Permanent Dipoles

Answer 7

• permanent difference in the distribution of electrons in a molecules orbital
• if the difference between electronegativity is greater or less than 0.5 a permanent dipole is induced with a bias towards the atom with greater electronegativity
• symmetrical molecules cannot have permanent dipoles

Question 8

Dip-Dip IMF

Answer 8

• Electrostatic attraction between two molecules with a dipole
• stronger than Van Der Waals

Question 9

Hydrogen bonding IMF

Answer 9

• electrostatic attraction between hydrogen ions and lone pairs
• only in molecules with N-H,O-H or F-H
• strongest IMF because attraction between lone pair and basically just a proton
• increases boiling points of compound more than just a covalent bond

Question 10

Crystal structure

Answer 10

• ionic - sodium chloride, held together by electrostatic attraction
• molecular - iodine, lowest melting point as held together by weak IMF
• metallic - Magnesium, stronger if metal ion has greater positive charge
• macromolecular - diamond, held together by strong covalent bonds
• graphite is layers of macromolecular structured carbon held together by weak Van der Waals forces so they are easily separated
• ice has a strong crystal structure due to the hydrogen bonding raising its melting point by more than a covalent bond would

Question 11

Electron repulsion

Answer 11

• bond pairs and lone pairs arrange themselves as far apart as possible to minimise repulsion
• bond and lone pairs are clouds of charge, an area that can contain an electron
• lone pairs repel more strongly than bond pairs
• more pairs of electrons on an atom reduces the bond angle of a molecule