CH2: Bonding

Question 1

What is an ionic bond?

Answer 1

Electrostatic attraction formed between the oppositely charged ions , which occurs in all directions

Question 2

How does charge vary with ionic radii?

Answer 2

Ionic radii INCREASE- INCREASING negative charge
Ionic radii DECREASE - INCREASING positive charge

Question 3

Why does ionic radius increase with increasing negative charge ?

Answer 3

• negative ions formed by gaining electrons
• outer most electrons are further away from positive nucleus, soo held weakly to nucleus , increasing ionic radius
• GREATER - CHARGE = LARGER radius

Question 4

Why does radius decrease with increasing positive charge ?

Answer 4

• positive ions formed by losing electrons
• fewer electrons experiencing electrostatic force of attraction to nucleus —> decrease ionic radius
  GREATER + CHARGE , SMALLER radius

Question 5

Physical properties of ionic compounds?

Answer 5

GIANT LATTICE STRUCTURE : ionic bond is electrostatic force of attraction between + charge metal (CATION) AND - charge non metal (ANION) ion
- creates giant lattice structure

MP/BP - high temps needed to overcome electrostatic forces between opposite charged ions
- lattices with greater ionic charge, have higher BP/MP

ELECTRICAL CONDUCTIVITY - can conduct in molten/aqueous state , bc ions can move to carry charge

SOLUBILITY- polar molecules (water) can break down ionic lattice/surround each ion in solution
- + end of polar molecule can surround negative anion
- end of polar molecule can surround positive cation

Question 6

What does solubility of ionic compound depend on?

Answer 6

• relative strength of electrostatic force of attraction in lattice
• attractions between ions and polar molecules

GREATER IONIC CHARGE (because stringer electrostatic forces), LESS SOLUBLE THE IONIC COMPOUND IS

Question 7

What is evidence for the existence of ions?

Answer 7

Behaviour of ionic substances in electrolysis
- positive ions in solution attracted to negative electrode
- negative ions attracted to positive electrode

E.g separation of copper chromate
Cu2+ ions (blue) attract to negative electrode
CrO4 2- ions (yellow) attract to positive electrode

Question 8

What is a covalent bond?

Answer 8

Electrostatic attraction between nuclei of two atoms and the bonding of electrons of their outer shells
- betwee 2 non metals

Question 9

What is dative covalent bonding ?

Answer 9

• some molecules have a lone pair of electrons that can be donated to form a Bond with an electron-deficient atom
• both electrons are from same atom

Question 10

Eg of dative covalently bonded molecule ?

Answer 10

Aluminium chloride - at high temps ALCl3 exists as a monomer
- aluminium needs 2 electrons to complete atom’s outer shell

At lower temps , Al2Cl6 is formed from two molecules of ALCl3 joining
- lone pairs of electrons on 2 chlorine atoms form dative bonds with aluminium atoms

Question 11

What is bond energy?

Answer 11

Energy required to break one mole of a covalent bond in the gaseous state
- larger the bond energy , stronger the covalent bond

Question 12

What is bond Length? How do forces of attraction effect bond length?

Answer 12

The inter nuclear distance of two covalently bonded atoms (distance between the nucleus of one atom to another)

• large electron density between nuclei of two atoms , so greater force of attraction between electrons and nuclei
• decreases bond length and increase strength of covalent bond

Question 13

What is the valence shell electron pair repulsion theory (VSEPR) ?

Answer 13

Predicts shape and bond angles of molecules
- bc in a molecule , bonding pairs of electrons will repel other electrons around the central atom, making the molecule adopt a shape, where the repulsive forces are minimised

Question 14

Why do lone pairs of electrons repel each other more than bonded pairs?

Answer 14

Lone pairs of electrons have more concentrated electron charge cloud
- could charges are wider/closer to nucleus

Question 15

Shape, description and bond angle of molecule with 2 electron pairs

Answer 15

Linear, 180 degrees

Question 16

Shape, description and bond angle of molecule with 3 electron pairs

Answer 16

Trigonal planar, 120°

Question 17

Shape, description and bond angle of molecule with 4 electron pairs

Answer 17

Tetrahedral, 109.5°

Question 18

Shape, description and bond angle of molecule with 5 electron pairs

Answer 18

Trigonal bipyramid , 90°,120°, 180°

Question 19

Shape, description and bond angle of molecule with 6 electron pairs

Answer 19

Octahedral, 90°, 180°

Question 20

What are isoelectronic ions?

Answer 20

Molecules and ions that have exactly the same no. And arrangement of electrons

Question 21

Shape and bond angle for a bent molecule (2 bond pairs, 2 lone pairs)

Answer 21

Non linear - 104.5 degrees

Question 22

bond angle of molecule with 3 bonding pairs and one lone pair?

Answer 22

107 degrees
Trigonal pyramidal

Question 23

Trend in melting point in period 2 and 3? And explain?

Answer 23

MP increases from Na to Al - metallic elements , where Al forms a 3+ ion, so stronger bonding (stronger electrostatic forces), bc more delocalised electrons bonded

Si has highest melting point - giant molecular structure - strong covalent bonds

MP decreases from P, S, Cl and Ar- simple molecules (P4, S8, Cl2 and Ar as a single atom) so weak intermolecular forces
(S is higher than P bc sulphur is larger - S8)

Question 24

Dipole?

Answer 24

Difference in charge between 2 atoms of a covalent bond caused by shift in electron density in the bond due to electronegativity difference between the 2 atoms.