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Chemistry > 2.2.2 Bonding and structure > Flashcards

2.2.2 Bonding and structure Flashcards

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1
Q

what is an ionic bond definition?

A

ionic bonding is the electrostatic force of attraction between oppositely charged ions formed by electron transfer

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2
Q

when is ionic bonding stronger?

A

when the ions are smaller and/or have higher charges

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3
Q

what pattern are the ions in an ionic solid arranged in?

A

a giant ionic lattice

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4
Q

why do ionic compounds have high melting points?

A

there are strong electrostatic attractive forces between the oppositely charged ions in the lattice

which means a lot of energy is required to break these bonds

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5
Q

why do ionic compounds not conduct electricity when in a solid?

A

the ions are held together tightly in the lattice and cannot move so no charge is conducted

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6
Q

why are ionic compounds good conductors of electricity when in a solution or molten?

A

the ions are free to move when molten or in a solution so a charge can be carried

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7
Q

why are ionic compounds soluble in water?

A

because water molecules have a slight electrical charge so can attract the ions away from the lattice

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8
Q

what can melting points in ionic compounds be affected by?

A

nuclear charge

ionic radius

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9
Q

what is the definition for covalent bonding?

A

a covalent bond is the strong electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms

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10
Q

why do simple covalent compounds have low melting and boiling points?

A

because there are weak intermolecular forces between the covalent bonds so little energy is needed to break the bonds

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11
Q

what state are simple covalent compounds usually in at room temperature?

A

usually gases or volatile liquids due to the weak intermolecular forces

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12
Q

why do simple covalent compounds not conduct electricity?

A

there are no free ions or electrons present in a simple covalent compound so they do not conduct electricity

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13
Q

why do giant covalent compounds have high melting and boiling points?

A

because they have strong covalent bonds in the giant molecule so a lot of energy is needed to break these apart

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14
Q

examples of giant covalent compounds

A

diamond

graphite

silicon dioxide

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15
Q

why does graphite conduct electricity?

A

because it has delocalised electrons that can move throughout the whole structure and carry charge

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16
Q

when is a dative covalent bond formed?

A

when one atom contributes both of the electrons needed for the covalent bond

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17
Q

what is needed for a dative covalent bond to form?

A

one atom has to have a lone pair of electrons and the other atom must have a vacant orbital

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18
Q

how is a dative covalent bond represented in a drawing?

A

an arrow which shows the direction of the electron pair donation

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19
Q

what is the definition of a metallic bond?

A

the electrostatic force of attraction between a lattice of positively charged ions and free/delocalised electrons

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20
Q

what are the factors that affect the strength of a metallic bond?

A

size of the charge on the positive ions - the bigger this is the stronger the bond

the number of mobile electrons - the more there are, the stronger the bond

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21
Q

why are metallic compounds good conductors of electricity?

A

because they have delocalised electrons

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22
Q

why do metallic compounds have high melting and boiling points?

A

because they have a giant lattice structure and a strong electrostatic attraction between the delocalised electrons and the metal ions which means a lot of energy is required in order to break the bonds

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23
Q

what is the definition of electronegativity?

A

the ability of an atom to attract the pair of electrons in a covalent bond (electron density)

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24
Q

what scale is electronegativity measured on?

A

the Pauline scale

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25
Q

what element is the most electronegative?

A

fluorine (4.0)

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26
Q

what element is the least electronegative?

A

francium (0.7)

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27
Q

which direction on the periodic table does the electronegativity gets weaker and weaker?

A

down and across from fluorine

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28
Q

what 2 factors affect the electronegativity of an atom?

A

the size of the nuclear charge (number of protons)

the size of an atom

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29
Q

how does the size of nuclear charge affect the electronegativity of an atom?

A

the bigger the nuclear charge is the larger the attraction between the nucleus and the pair of electrons - the electronegativity goes up

30
Q

how does the size of the atom affect the electronegativity of an atom?

A

as the size increases, the pair of electrons are further from the nucleus, and there will be shielding effect from the inner electron, the electronegativity goes down

31
Q

if both atoms have equal electronegativity where will the electrons be?

A

the bond is formed roughly half way between the 2 atoms

this is the case in non polar covalent bonds

32
Q

where is the electron if the atoms have slightly different electronegativities?

A

the electron pair will be pulled towards the more electronegative atom

this end will have more electron density and will become slightly negatively charged

33
Q

what does the polarity of a molecule depend on?

A

its shape

34
Q

is a molecule with overall symmetry polar or non polar?

A

non polar

35
Q

is a non symmetrical molecule polar or non polar?

A

polar

36
Q

what are the weakest type of intermolecular forces?

A

London forces

37
Q

what do London forces form between?

A

between neighboring non polar forces

38
Q

what is the distance that London forces have an affect over?

A

a couple of nanometers

39
Q

how is a temporary dipole formed?

A

an electron is always on the move

a temporary dipole is formed when at any one time one end of the molecule might have a lower electron density than the other

40
Q

what symbol do you need when drawing an induced dipole?

A

party drawn 8 with a minus sign in top right hand corner

41
Q

how is an induced dipole formed?

A

the 8- end of the molecule will attract electron density to one end of the neighboring molecule

the neighboring molecule now has a dipole that has been induced by the first molecule - an induced dipole

42
Q

if the molecule is larger, is the London force stronger or weaker?

A

stronger

43
Q

why is the London force stronger if the molecule is bigger?

A

more surface contact

more electrons lead to stronger London forces

44
Q

how much stronger are permanent dipole - dipole forces than London forces?

A

10 times stronger than London forces

45
Q

where do permanent dipole - dipole forces form between?

A

between two polar covalent molecules (i.e. in molecules with a difference in electronegativity)

46
Q

do compounds with only London forces have a higher or lower boiling point than compounds that also have permanent dipole - dipole forces?

A

lower

47
Q

where does hydrogen bonding only happen?

A

only happens when a hydrogen atom is covalently bonded to a N, O or F atom

48
Q

which is the strongest intermolecular force of attraction?

A

hydrogen bonding

49
Q

how much stronger is hydrogen bonding than London forces?

A

100 times stronger

50
Q

what do you need to include when drawing hydrogen bonding?

A

always show lone pairs

must always show the polarity of the element (8-)

hydrogen must always be from lone pair

51
Q

what does the shape of a molecule depend on?

A

the number of electron pairs around the central atom in the molecule

52
Q

what is the molecule shape called with 2 bond pairs and no lone pairs?

A

linear

53
Q

what is the bond angle in a linear molecule?

A

180 degrees

54
Q

what is the molecule shape called with 3 bond pairs and no lone pairs?

A

trigonal planar

55
Q

what is the bond angle in a trigonal planar shaped molecule?

A

120 degrees

56
Q

what is the molecule shape called with 4 bond pairs and no lone pairs?

A

tetrahedral

57
Q

what is the bond angle in a tetrahedral shaped molecule?

A

109.5 degrees

58
Q

what is the molecule shape called with 5 bond pairs and no lone pairs?

A

trigonal bipyramidal

59
Q

what are the bond angles in a trigonal bipyramidal shaped molecule?

A

120 degrees and 90 degrees

60
Q

what is the molecule shape called with 6 bond pairs and no lone pairs?

A

octahedral

61
Q

what is the bond angle in an octahedral shaped molecule?

A

90 degrees

62
Q

do lone pairs or bonded pairs repel more strongly?

A

lone pairs

63
Q

what is the molecule shape called with 3 bond pairs and 1 lone pair?

A

pyramidal

64
Q

what is the bond angle in a pyramidal shaped molecule?

A

107 degrees

65
Q

what is the molecule shape called with 2 bond pairs and 2 lone pairs?

A

V - shaped

66
Q

what is the bond angle in V-shaped molecule?

A

104.5 degrees

67
Q

what is the method for working out the shape of an ion?

A

1 - draw the outer shell electrons of the central atom

2 - workout the charge and remove or gain electrons depending on the charge

3 - pair up the electrons in the usual way

4 - workout the shape and bond angle(s) from the number of bonded pairs and lone pairs

68
Q

why does water have a high melting point and boiling point for being a simple molecule?

A

because of its hydrogen bonding

69
Q

why is ice less dense than water?

A

ice has an open lattice with hydrogen bonds holding the water molecules apart, when ice melts the rigid hydrogen bonds collapse, allowing the water molecules to move close together

the distance the molecules are held apart is what makes ice less dense than water

70
Q

why does iodine have a low melting point?

A

each iodine atom bonds covalently to another to form an I2 molecule

thee molecules then bond to each other through weak intermolecular bonds (London forces)

a low amount of energy is needed to break these bonds

Chemistry (6 decks)

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