CH2: Bonding Flashcards

1
Q

What is an ionic bond?

A

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

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2
Q

How does charge vary with ionic radii?

A

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

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3
Q

Why does ionic radius increase with increasing negative charge ?

A
  • 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
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4
Q

Why does radius decrease with increasing positive charge ?

A
  • positive ions formed by losing electrons
  • fewer electrons experiencing electrostatic force of attraction to nucleus —> decrease ionic radius
    GREATER + CHARGE , SMALLER radius
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5
Q

Physical properties of ionic compounds?

A

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

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6
Q

What does solubility of ionic compound depend on?

A
  • 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

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7
Q

What is evidence for the existence of ions?

A

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

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8
Q

What is a covalent bond?

A

Electrostatic attraction between nuclei of two atoms and the shared pair of electrons
- betwee 2 non metals

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9
Q

What is dative covalent bonding ?

A
  • 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
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10
Q

Eg of dative covalently bonded molecule ?

A

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

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11
Q

What is bond energy?

A

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

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12
Q

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

A

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
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13
Q

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

A

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

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14
Q

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

A

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

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15
Q

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

A

Linear, 180 degrees

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16
Q

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

A

Trigonal planar, 120°

17
Q

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

A

Tetrahedral, 109.5°

18
Q

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

A

Trigonal bipyramid , 90°,120°, 180°

19
Q

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

A

Octahedral, 90°, 180°

20
Q

What are isoelectronic ions?

A

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

21
Q

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

A

Non linear - 104.5 degrees

22
Q

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

A

107 degrees
Trigonal pyramidal

23
Q

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

A

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 / radius decreases

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 LONDON forces
(S is higher than P bc sulphur is larger - S8)

24
Q

Dipole?

A

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.