ATOMIC STRUCTURE AND BONDING

Question 1

Interpreting mass spectra for diatomic molecules

Answer 1

EXAMPLE Cl2
-Two isotope peaks (35Cl+ and 37Cl+)
-Peaks for all possible (3) combinations of these isotopes

Question 2

Molecular ion peak

Answer 2

Highest value peak

Question 3

Base peak

Answer 3

Tallest peak (most abundant)

Question 4

Factors that affect the size of ionisation energy

Answer 4

-Size of nuclear charge
-Size of atom and how many shells it has
-Shielding
-Stability of a 1/2 filled subshell

Question 5

State and explain the trend in size of atoms across a period

Answer 5

Atomic radius decreases as the number of protons increases, the outer shell electrons become more attracted, resulting in a decrease

Question 6

Effective nuclear charge explained

Answer 6

-Net charge on the nucleus
-The 10 inner electrons cut down on the outer shell electrons effect, so minus 10 from the number of electrons to find the effective nuclear charge

Question 7

First ionisation energies decrease down a group because

Answer 7

Whilst nuclear charge increases down a group (1) this is more than often offset by the increase in shielding due to increasing number of inner shells (1). Also because atomic radii increase down a group the outer shell electron is further from the nucleus and are less strongly attracted to it :. requires less energy to remove the electron (1)

Question 8

First ionisation energies increase across a period because

Answer 8

First ionisation energies generally increase because nuclear charge increases, shielding remains almost constant and atomic radius decreases therefore the outer electron is more strongly attracted to nucleus and requires more energy to remove

Question 9

Successive ionisation energies explained

Answer 9

Successive removal of electrons generates an increasing positively charged cation which results in a decrease in radii and shielding and the outer shell electrons becoming increasingly attracted to the nuclear charge and making subsequent ionisations progressively more endothermic

Question 10

SPDF notation- exceptions

Answer 10

Cr- 1s2 2s2 2p6 3s2 3p6 3d5 4s1 (prefers being stable in a half-full subshell)
Cu- 1s2 2s2 2p6 3s2 3p6 3d10 4s1

Question 11

Transition metals SPDF note

Answer 11

For transition metals, 4s fills first for atoms, 4s empties first for forming ions

Question 12

For sketching first IE across period 3

Answer 12

-Mg above Na but not above Si
-Al below Mg and above Na
-P above S but below Cl

Question 13

Strength of the electrostatic forces of attraction increases as…

Answer 13

-The charge on the ions increases
-The size of the ions decrease

Question 14

Ionic bonding properties

Answer 14

Crystalline- regualr lattic of ions and anions creates crystal structure
High melting and boiling point solids- Large amounts of energy required to break the strong electrostatic attractions between oppositely charged ions in a 3D lattice
Doesnt conduct when solid but does when motlen or aqueous- In the solid state the ions are in fixed positions and cannot move and carry charge, when molten or aqueous, the ions become free to move and carry charge
Tend to be soluable in water- Water collides with the crystal structure breaking the electrostatic attraction and forming ion dipole bonds

Question 15

Dissolution

Answer 15

The process in which the particles of a substance move into the solvent

Question 16

Charge density- cations

Answer 16

Simple cations are metal atoms which have lost one or more electrons, they have more protons then electrons hence the positive charge. The ion has a smalller radius than its parent atom because the positive charge in nucleus draws the electrons in

Question 17

Charge density- anions

Answer 17

Anions have more electrons than protons hence the negative charge. The ion has a larger radius than its parent atom because the extra electron is repelled by neighbouring electrons causing the electron cloud to expand

Question 18

Atomic radius across and down a group

Answer 18

-Increases down a group (The number of shells increases)
-Decreases across a period (Increasing effective nuclear charge, electron entering the same shell with the same degree of shielding by inner electrons)

Question 19

The strength of the metallic bond increases as…

Answer 19

-The charge on the positive ion increases
-The size of the positive ion decreases
-The number of delocalised electrons per atom increases

Question 20

Metallic bonding properties

Answer 20

Hardness- Strong electrostatic forces of attraction between lattice of cations and sea of delocalised electrons
High metling point- Large amount of energy needed to break strong electrostatic forces of attraction between lattic of cations and delocalised electrons
Good electrical conductor- Delocaised electrons are free to move when a potential difference is applied and carry charge
Malleability and ductility- Layers of metal ions can slide over one another, and the delocalise electrons flow into new spaces o maintain metallic bonds

Question 21

The strength of the covalent bond depends on..

Answer 21

The degree of overlap of atomic orbitals. The greater the amount of overlap, the stronger the bond. Small atoms form strong covalent bonds because their nuclei are close to the bonding electrons resulting in a stronger force of attarction

Question 22

Properties of simple molecular elements

Answer 22

Low melting and boiling points- The covalent bonds WITHIN the molecule are strong, but the FOA between the molecules are weak. The amount of energy requirede to break these weak intermolecular forces is small
Insulators- There are no free ions or delocalised electrons to move and carry charge

Question 23

Structure of graphite

Answer 23

Layers of carbon, each carbon is covalntly bound to 3 other carbon atoms (trigonal planar), this leaves one electron delocalised between the layers. Grapite is the only covalent element which conducts electricity
Weak van der waals forces (instantaneous dipole-induced dipole) between layers means that layers can slip over the other when pressure is applied. Used in pencils and lubricants

Question 24

Diamond

Answer 24

Each carbon atom is covalently bonded to 4 other carbon atoms (tetrahedral) in a 3D structure, resulting in diamond having a very high melting point and is extremely hard and has many strong covalent bonds which require a lot of energy to break

Question 25

Diamond properties

Answer 25

High melting point- The many strong covalent bonds between C atoms in a 3D structure require a lot of energy to break
Hard ^^^
Insulator- There are no free ions or delocalised electrons to move and carry charge

Question 26

Graphite properites

Answer 26

High melting point- The many strong covalent bonds between C atoms in the haxagonal layers require a lot of energy to break
Soft- The weak van der waals attractions between layers allow them to slide over one another
Conductor- In the solid state, graphite can conduct as the delocalised electrons are free to move and carry the charge
Does not conduct when molten- when molten the structure is lost and graphite cannot conduct electricity

Question 27

Explain the mpts across period 3 Na-Al

Answer 27

-Melting point increases as the strength of the metallic bond increases, which depends on the strength of the electrostatic attraction between the delocalised e- and the lattice of cations. (describe how many e- each atom has and its relative strength in order)

Question 28

Explain the mpts across period 3 Si (like C)

Answer 28

Si is a giant covalent structure with many strong covalent bonds in a 3D network :. takes a lot of energy to break these strong covalent bonds :. high mpt

Question 29

Explain the mpts across period 3 P4, S8, Cl2

Answer 29

Are all simple molecular covalent with only weak van der waals attractions between molecules. Strength of vdw depends on the number of e- (describe each atoms e- in order and relative mpts)

Question 30

Explain the mpts across period 3 Ar

Answer 30

Is monoatomic with only weak vdw between atoms which require very little energy to break :. low mpt