chemical bonding

Question 1

attraction in an ionic bond

Answer 1

ionic bond is the electrostatic attraction between oppositely charged ions

Question 2

attraction in a covalent bond

Answer 2

covalent bond is the electrostatic attraction between the positively charged nuclei of both bonded atoms and their shared electrons

Question 3

attraction in a metallic bond

Answer 3

metallic bond is the electrostatic attraction between a lattice of positive ions and the sea of delocalised electrons

Question 4

electronegativity definition

Answer 4

electronegativity of an atom is a measure of its ability to attract the electrons in a covalent bond to itself

Question 5

factors affecting electronegativity across period

Answer 5

nuclear charge increases while shielding effect remains relatively constant. Effective nuclear charge increases, hence electronegativity increases across the period

Question 6

factors affecting electronegativity down the group

Answer 6

elements in the same group have roughly the same effective nuclear charge as both nuclear charge and shielding effect increase down the group. However, as the number of quantum shells increases, atomic radius increases. Hence, electronegativity decreases down the group.

Question 7

prediction of the type of bond formed through the difference in electronegativity

Answer 7

similar electronegativity between atoms -> electron sharing -> covalent bonding

large difference in electronegativity between atoms -> electron transfer -> ionic bonding

Question 8

describe metals

Answer 8

a giant metallic structure which is a lattice of metal cations and the sea of delocalised electrons held together by metallic bonding

Question 9

strength of metallic bonding depends on…

Answer 9

number of valence electrons contributed per atom. the larger the number of valence electrons contributed per atom, the greater the number of delocalised electrons, the stronger the metallic bonding

charge and radius of the metal cation. the higher the charge and the smaller the radius of the metal cation, the higher its charge density, or the amount of charge per unit surface area of that ion, and the stronger the metallic bonding

Question 10

high/low melting and boiling point

Answer 10

high melting point. a large amount of energy is needed to overcome the strong attraction between the metal cations and sea of delocalised electrons. more energy is needed to overcome the metallic bonding, resulting in higher melting and boiling points.

Question 11

good/bad electrical and thermal conductivity

Answer 11

good electrical conductors. the sea of delocalised electrons act as mobile charge carriers.
good thermal conductivity as thermal energy causes the electrons to move more quickly, allowing energy to be transferred to the other parts of the metal by the mobile electrons.

Question 12

malleable and ductile?

Answer 12

malleable and ductile. when a large stress is applied to a piece of solid metal, the layers of ions will slide over one another into new positions. the overall shape of the metal changes but it does not break apart as the sea of delocalised electrons prevents repulsion between the cations as they move past one another. The metallic bonding remains intact.

Question 13

describe ionic bonds

Answer 13

a giant ionic lattice structure which is a lattice of cations and anions held together by ionic bonding

Question 14

lattice energy definition

Answer 14

the heat evolved when 1 mole of pure ionic solid is formed from its constituent gaseous ions

Question 15

magnitude of lattice energy depends on…

Answer 15

charge of ions and their radii
(formula)
the higher the charge and the smaller the radii of the ions, the larger the magnitude of lattice energy and the stronger the ionic bonding

Question 16

high/low melting and boiling point

Answer 16

high melting and boiling points. a large amount of energy is needed to overcome the strong electrostatic attractions between oppositely charged ions.

Question 17

good/bad electrical conductivity

Answer 17

good electrical conductivity in the molten or aqueous state. ions can act as mobile charge carriers.

bad electrical conductivity in the solid state. ions are in fixed positions and are not free to move.

Question 18

malleable and ductile?

Answer 18

hard and rigid but brittle. oppositely charged ions are held in fixed positions throughout the crystal lattice by strong ionic bonds. moving the ions out of position requires large amounts of energy to overcome these bonds.
if a strong enough force is applied, it will force ions of like charges to move next to each other. repulsion between ions of like charges will cause the lattice to shatter.

Question 19

what is a sigma bond + draw

Answer 19

the head-on overlap of two orbitals

Question 20

what is a pi bond + draw

Answer 20

the side-on overlap of two orbitals

Question 21

how many pi and sigma bonds does a triple bond contain

Answer 21

1 sigma bond, 2 pi bonds

Question 22

what does bond strength depend on

Answer 22

bond strength depends on the degree of orbital overlap between the two bonded atoms and how strongly the electrons in the overlap region are attracted to the nuclei of the atoms

Question 23

bond energy definition

Answer 23

the average amount of energy required to break 1 mole of a covalent bond in the gaseous state to form gaseous atoms.

Question 24

bond energy depends on…

Answer 24

bond length, smaller atoms form shorter and stronger bonds as the overlap between orbitals is more effective

bond order, as multiple bonds are shorter and stronger than single bonds. when more electrons are being shared, the attraction between the two positively charged nuclei and the shared electrons is stronger.

Question 25

longer bonds vs shorter bonds

Answer 25

longer bonds are weaker. they break more easily and react more readily.

Question 26

molecules whose central atom has fewer than 8 electrons

Answer 26

electron deficient, first 2 periods

Question 27

molecules whose central atom has more than 8 electrons

Answer 27

period 3 and below. these elements can use its d orbitals to accommodate additional electrons and can expand its octet by using energetically accessible d orbitals.

Question 28

for each (-) charge, which atom do you add it to?

Answer 28

more electronegative atom

Question 29

what is the VSEPR theory?

Answer 29

the electron pairs around the central atom of a molecule arrange themselves as far apart as possible so as to minimise their mutual repulsion

the repulsion between lone pair and lone pair is larger than long pair and bond pair which is larger than bond pair and bond pair
lp-lp > lp-bp > bp-bp

Question 30

shape of molecules + angle (2 electron pairs)

Answer 30

linear, 180°

Question 31

shape of molecules + angle (3 electron pairs)

Answer 31

trigonal planar, 120°
bent, 118°

Question 32

shape of molecules + angle (4 electron pairs)

Answer 32

tetrahedral, 109.5°
trigonal pyramidal, 107°
bent, 104.5°

Question 33

shape of molecules + angle (5 electron pairs)

Answer 33

trigonal bipyramidal, 90°, 120°
see saw 90°
t-shape, 90°
linear, 180°

Question 34

shape of molecules + angle (6 electron pairs)

Answer 34

octahedral, 90°
square pyramidal, 90°
square planar, 90°

Question 35

which hybrid orbital forms a loner and weaker bond (hybridisation) why

Answer 35

the bond with more p character as a p orbital is more elongated as compared to a spherical s orbital

Question 36

degree of covalent character depends on…

Answer 36

polarising power of the cation: small + high charge = high charge densities, higher tendency to distort the anion’s electron cloud, greater covalent character in the ionic bonding

polarisability of the anion: large = high polarisability, valence electrons are further from and less strongly attracted by the nucleus to the electron cloud is easily distorted by a cation, greater covalent character

Question 37

what are the three types of intermolecular forces of attractions between molecules

Answer 37

instantaneous dipole-induced dipole attractions (dispersion forces)
permanent dipole-permanent dipole attractions
hydrogen bonding

Question 38

what does the strength of dispersion forces depend on

Answer 38

number of electrons in the molecule (more electrons = more polarisable the electron cloud = stronger dispersion forces)

surface area of contact between adjacent molecules (larger the surface area of contact = more easily induced dipoles are formed = stronger dispersion forces)

Question 39

what must be present for hydrogen bonding to occur

Answer 39

must contain a hydrogen atom bonded to a highly electronegative atom (F, O, N)
must be an atom (F, O, N) with a lone pair of electrons

Question 40

what affects the strength of hydrogen bonding

Answer 40

electronegativity of the atom bonded to hydrogen (more electronegative = stronger bonds)

number of H atoms bonded to F, O, N and the number of lone pairs available

Question 41

intramolecular vs intermolecular hydrogen bonding

Answer 41

more intramolecular hydrogen bonding = less intermolecular hydrogen bonding, less energy needed to break the less extensive intermolecular hydrogen bonding, lower boiling point

Question 42

physical properties of simple molecular lattices
(melting and boiling points, solubility, electrical conductivity)

Answer 42

low melting, boiling points: weak intermolecular forces between molecules require little thermal energy to overcome

soluble in organic solvents

unable to conduct electricity as there are no mobile charge carriers.

Question 43

physical properties of elements across the period

Answer 43

Na, Mg, Al increases in melting and boiling point as more energy is needed to overcome the stronger metallic bonding (more valence electrons, higher charge density of the cation)

Si has a giant molecular structure, very high melting point, more energy is needed to overcome the many strong covalent bonds between the si atoms

P4, S8, Cl2 have simple molecular structure, Ar has a simple atomic structure. Little energy is needed to overcome the weak dispersion forces between the molecules or between argon atoms, lower melting points.

number of electrons and strength of dispersion forces decreases from S8, P4, Cl2, Ar. energy needed to overcome dispersion forces decreases, melting point decreases.

Question 44

how to determine if a substance is soluble in a given solvent?

Answer 44

in terms of energy changes, a solute is soluble in a solvent if the energy released from solute-solvent interactions is greater than or comparable to the energy needed to overcome solute-solute interactions and solvent-solvent interactions.

Question 45

structure of determining solubility

Answer 45

the energy released when forming (interactions) between (solute and solvent) is comparable to the energy required to overcome the (bonding) between (solute) and the (bonding) between (solvent)