1.2.2 BONDING & STRUCTURE

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What is ionic bonding?
electrostatic bonding between oppositely charged ions
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How would you illustrate ionic bonding?
outermost shell illustrated (even if now empty) with square brackets with charge on outsode
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between which elements does ionic bonding take place?
1-2 metals react with 5-7 non-metals
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state the charge and formulae of nitrate
NO3-
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state the charge and formulae of sulphate
SO4^-2
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state the charge and formulae of ammonium
NO4^+
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state the charge and formulae of carbonate
CO3^-2
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What is a covalent bond?
shared pair of electrons
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What is dative covalent bonding?
both electrons in the bond are supplied by the same atom
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How is dative covalent bonding represented?
-> arrow towards atom that is accepting
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Give an example of a molecule/ion with a dative bond
NH4+ // H3O+ // NH3BF3
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how is covalent bonding illustrated?
two outer shells overlapping 'dot and cross'
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How is the shape of a simple molecule determined?
by the repulsion between electron pairs surrounding the central atom
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Describe the characteristics of lone pairs of electrons
they repel more than bonded pairs, decreases bonding angle by 2.5
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What is the shape and bond angle of a molecule with 2 bonding regions
linear - 180
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What is the shape and bond angle of Carbon Dioxide?
linear - 180
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What elements covalently bond?
non-metals
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What is the shape and bond angle of a molecule with 3 bonding regions?
trigonal planar - 120 (all on same plane)
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What is the shape and bond angle of a molecule with 3 bonding regions and a lone pair?
v-shaped - 117.5
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what is the shape and bond angle of a molecule with 4 bonding regions?
tetrahedral - 109.5
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Describe the planar structure of tetrahedral molecules
two on plane, one inwards and one outwards
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what is the shape and bond angle of a molecule with 4 bonding regions and a lone pair?
trigonal pyramidal - 107 - one in each plane
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What is the shape and bond angle of a molecule with 4 bonding regions and 2 lone pairs?
bent (non-linear) - 104.5
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what is the shape and bond angle of a molecule with 6 bonding regions
octahedral - 90
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How are simple molecules bonded?
covalently
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Describe the planar structure of an octahedral molecule
two bonds each in same plane - each opposite to each other
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How do you explain the shape of a molecule?
1. state number of pairs of electrons 2. state n of lone pairs 3. if all repel equally or not 4. shape and angle
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What is electronegativity?
ability of an atom to attract the bonding electrons in a covalent bond
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What factors affect electronegativity?
increases across a period as proton n and atom radius decrease // decreases down a group as atoms get larger there is more shielding and distance increases
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when will a compound be purely covalent?
compound contains elements of similar electronegativities
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how does a permanent dipole form?
when covalently bonded atoms have different electronegativites, resulting on a polar-bond
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what happens when a covalent bond is polar?
bond has unequal distribution of electrons which results in a charge seperation
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what is bond polarisation?
when a covalent bond becomes slightly ionic in charge because it has a dipole moment
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How can you find if a bond has a dipole?
difference in EN // 0.5-1.6 = dipoles // 2.0 < = dipoles // IF EN is 1.6-2.0 between metals then dipole
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What are Van der Waals?
very weak attractive forces between induced dipoles in neighbouring molecules
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How do Van der Waals occur?
constant imbalance of electrons in molecules results in instantaneous dipoles which induces dipoles in neighbouring molecules
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What are the characteristics of Van der Waals?
they are between all molecules and atoms // force of VdW increase the more electrons present// present in noble gases
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What are permanent dipole-dipole interactions?
weak attractive forces between permanent dipoles in neighbouring polar molecules
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How do permanent dipole-dipole interactions occur?
polar molecules have permanent dipoles // dipole in one molecule attracts dipole in another
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What is a hydrogen bond?
strong dipole-dipole attraction between an electron deficient hydrogen atom and a lone pair of electrons on a highly EN atom on a different molecule
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How do hydrogen bonds occur?
When polarised covalent bonds cause H atoms to form bonds with lone pairs of electrons on FON atoms of other molecules
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How does structure and bonding affect the noble gases?
going down the group electron n increases // VdW increase // BP increases// VdW are the only forces // without VdW would not be able to liquify
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what is an intermolecular force?
an attractive force between neighbouring molecules
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State the special properties of H2O
ice is less dense than water // relatively high MP and BP // solubility
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How is ice less dense than water?
ice has open lattice structure with H bonds holding molecules apart (when melts these bonds collapse)
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Why does water have a relatively high melting and boiling point?
H bonds hav veto be overcome
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Explain the solubility of water
can dissolve ionic substances as dipoles (H and O) attracts oppositely charged ions - breaking apart giant ionic lattice structures
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What is metallic bonding?
electrostatic force of attraction between positive metal ions and delocalised electrons
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What factors affect the strength of a metallic bond?
number of protons/ nuclear attraction - more protons stronger bond// number of delocalised electrons per atom// size of the atom - smaller=stronger
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describe the structure of a giant ionic lattice
structure of an ionic compound made up of + and - ions held in place by strong electrostatic forces of attraction between oppositely charged ions
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give an example of a giant ionic lattice
crystalline substances (salts) ie NaCl
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What are the characteristics of giant iconic lattices?
solids at RTP // large amount if energy required to break bonds// non conductors as no free ions// can conduct as liquids
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What is a giant covalent lattice?
three-dimensional structure of atoms bonded together by strong covalent bonds
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give some examples of giant covalent lattices
diamond // silicone dioxide// graphite
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what are the characteristics of giant covalent lattices?
very high MP/BP, strong bonds// non conductors as no free electrons// insoluble
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what is the structure of diamonds?
tetrahedral structure, macromolecular structure of covalent bonds// 4 covalent bonds per atom
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describe the characteristics of diamonds
poor conductivity// very strong and hard// shape allows forces to spread throughout lattice
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What is the structure of graphite?
hexagonal planar structure in layers of covalent bonds// 4th electron per atom is delocalised - delocalised between layers
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Describe the characteristics of graphite
good conductor as electrons free to move between layers// high MPBP // soft, sliding layers
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What is a simple molecular lattice?
a three dimensional structure of molecules, bonded together by weak intermolecular forces
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describe a simple molecular lattice
individual molecules with strong covalent bonds// all types of intermolecular forces
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describe the characteristics of simple molecular lattices
low MPBP due to weak intermolecular forces // low solubility // non conductive
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What is a giant metallic lattice?
three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds
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Describe the characteristics of giant metallic lattices
high MPBP due to electrostatic forces// good conductors due to electrons// ductile and malleable planes of + can slide over each other
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Card 2

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How would you illustrate ionic bonding?

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outermost shell illustrated (even if now empty) with square brackets with charge on outsode

Card 3

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between which elements does ionic bonding take place?

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Card 4

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state the charge and formulae of nitrate

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Card 5

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state the charge and formulae of sulphate

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