2.2. Electrons, Structure and Bonding

Question 1

How many electrons can fill the first 4 shells?

Answer 1

n = 1 -> 2
n= 2 -> 8
n=3 -> 18
n=4 -> 32

‘n’ = principle quantum number, the shell/energy level number

Question 2

What are atomic orbitals?

Answer 2

regions around the nucleus that can hold up 2 electrons, with opposite spins

Question 3

The greater the shell number n, what happens to the s and p orbital?

Answer 3

Greater the radius of its s-orbital
Further the p orbital is from the nucleus

Question 4

what is the shape of s orbitals?

Answer 4

Sphere

Question 5

what are the shapes of p orbitals?

Answer 5

Dumbbells on y, x and z axis

Question 6

How many electrons can fill the s, p, and d sub shells?

Answer 6

s = 2
p = 6
d = 10

Question 7

What property do electrons have?

Answer 7

• SPIN, so they are shown as arrows. Any 2 electrons sharing an orbital will have opposite spins.

Question 8

Write the electron configuration of krypton (36 e-)

Answer 8

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

Question 9

What is the shorthand configuration for krypton?

Answer 9

• You can use configurations of the nearest noble gases to make things easier, and then the rest of the sub shells + electrons after.

[Ar] 3d¹⁰ 4s² 4p⁶

Question 10

What are the 2 exceptions?

Answer 10

Copper and chromium
They are more stable with half full sub shells, and so for chromium instead of 4s23d4, it is 4s13d5.
This is a similar case for copper too.

Question 11

What should you be careful with when it comes to ions?

Answer 11

• Write out the configuration of the atom first, and then remove or add electrons to give the ion, so that the order of filling becomes correct.
• The 4s also EMPTIES before 3d.

E.g.

Ni (28) = [Ar] 3d⁸ 4s²
Ni2+ = [Ar] 3d⁸ because the 4s loses the 2 electrons.

Question 12

What is ionic bonding?

Answer 12

strong electrostatic attraction between positive and negative ions

Question 13

What is the structure of ionic compounds?

Answer 13

• GIANT ionic lattice
• Repeating pattern of ions where each ion attracts oppositely charged ions in all directions

Question 14

What is a property of ionic compounds? 1. MP

Answer 14

Melting and boiling points: lots of energy to overcome strong electrostatic forces of attraction between oppositely charged ions in the giant ionic lattice.

Question 15

What is a property of ionic compounds? 2. Solubility

Answer 15

Solubility: many dissolve in polar solvents. polar water molecules for example are attracted to the ions and bond to them, weakening ionic bonding and the ions become surrounded and break free, causing the lattice to break down. Ions w large charges = attraction may be too strong = not very soluble.

Question 16

What is a property of ionic compounds? 3. Conductivity

Answer 16

Electrical conductivity: solid - doesnt conduct, ions are in fixed positions and so arent mobile. Aqueous/molten: ions are now free to move and carry charge.

Question 17

what is a covalent bond?

Answer 17

strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms. Overlap of atomic orbitals, each containing one electron, to give a shared pair of electrons.

Question 18

what is diff about a covalent bond compared to ionic bonding?

Answer 18

LOCALISED - acts soley between the shared pair of electrons and the nuclei of the atoms, unlike ionic bonding which is in all directions

Question 19

How many bonds do atoms such as carbon, nitrogen, oxygen and hydrogen form? Why?

Answer 19

C - 4 bonds
N- 3 bonds
O- 2 bonds
H- 1 bonds

• The number of bonds that can be made depends on valence electrons

Question 20

What do you have to be cautious of with covalent bonding?

Answer 20

Predictions cannot always be based on noble gas structures.

Question 21

What is the case with boron?

Answer 21

• only 3 outer electrons can be paired, so only 6 on it’s outer shell in it’s common compounds.
• it isn’t a noble gas structure, but it forms 3 covalent bonds, fully utilising its outer shell.

Question 22

What is special about phosphorus, sulfur and chlorine regarding formulae of fluorides with these non metals?

Answer 22

• They are HYPERVALENT

Phosphorus: 5 electrons in outer shell. Either PF3 or PF5
Sulfur: 6 electrons in outer shell. Either SF2, SF4 or SF6 .
Chlorine: 7 electrons in outer shell. Either ClF , ClF3, ClF5, or ClF7.

‘expansion of the octet’ is possible since they have an n=3 outer shell with a d sub-shell, so more is available for bonding.

• Depends on how electrons are paired/arranged - diff numbers of unpaired electrons lead to diff possibilites.

Question 23

What are double covalent bonds? What are some examples?

Answer 23

• Electrostatic attraction is between 2 shared pairs of electrons and the nuclei of bonding atoms.
• All atoms have 8 electrons in their outer shell for double bonding and an electron structure of the nearest noble gas.

CO2, O2

Question 24

WHat are triple covalent bonds? What are some examples?

Answer 24

• the electrostatic attraction between 3 shared pairs of electrons and the nuclei of bonding atoms.
• all atoms have electron structure of nearest noble gas once again

HCN

Question 25

What is a dative covalent bond? What is a common example?

Answer 25

- Where a shared pair of electrons has been supplied by ONE of the bonding atoms only; it was originally a lone pair. NH4+

Question 26

what is electronegativity?

Answer 26

- the ability of an atom to attract a pair of electrons in a covalent bond

Question 27

what is used to compare e.n of atoms of diff elements?

Answer 27

- pauling scale

Question 28

What is the trend across the periodic table for e.n?

Answer 28

- Across periods, the nuclear charge increases and atomic radius decreases - Down groups, shielding increases and atomic radius increases. - Consequently, fluorine is the most electronegative atom.

Question 29

What is a covalent bond?

Answer 29

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

Question 30

What occurs in a non polar bond?

Answer 30

Bonded electron pair is shared EQUALLY between the bonded atoms - when the atoms are of the same or VERY similar electronegativities

Question 31

What happens in a polar covalent bond?

Answer 31

Bonded electron pair is shared unequally between the bonded atoms, due to different electronegativity values. Creates a DIPOLE in the bond (separation of opposite charges)

Question 32

What makes a molecule with polar covalent bonds, non polar? How does the shape of a molecule affect its polarity?

Answer 32

Depending on the shape of the molecule, the dipoles in a molecule may reinforce one another to produce a larger permanent dipole (polar molecule) Or the dipoles cancel out (molecule is symmetrical) = non polar molecule.

Question 33

How do ionic compounds dissolve in polar solvents?

Answer 33

Polar molecules attracted towards ions on surface of ionic lattice Water molecules for example bond to the ions, weakening ionic bonding. Ionic bonds break and the lattice breaks down The ions become surrounded by water molecules

Question 34

What are intermolecular forces?

Answer 34

- weak interactions between dipoles of different molecules - largely responsible for physical properties

Question 35

How are induced dipole-dipole interactions formed?

Answer 35

- Electrons constantly moving = uneven distribution of electrons (changing electron density) - Instantaneous dipole created - Induces a dipole on a neighbouring molecule - This continues, causing molecules to attract one another

Question 36

What affects the strength of an induced dipole-dipole interaction?

Answer 36

- more electrons in each molecule = stronger London forces between molecules = more energy needed to overcome them = increased boiling point

Question 37

what are permanent dipole-dipole interactions? why do polar molecules have higher boiling points than non polar molecules?

Answer 37

- act between permanent dipoles in diff polar molecules - polar molecules have london forces AND permanent dipole interactions between them = greater number of Van der Waals = more energy needed to overcome them.

Question 38

What is hydrogen bonding? How does it occur?

Answer 38

an attraction between a lone pair of electrons on an electronegative atom in one molecule and a H atom in another molecule attached to an electronegative atom. Shape around H atom involved is linear.

Question 39

What are some anomalous properties of water?

Answer 39

Ice less dense than water: hydrogen bonds hold water molecules apart in an OPEN LATTICE STRUCTURE. This means ice floats, creating an insulating layer + preventing water from freezing solid. higher melting and boiling point than expected: appreciable quantity of energy is needed to break the strong hydrogen bonds.

Question 40

What structure do simple molecular substances have? What forces and bonds are involved?

Answer 40

- Regular structure when solid called a simple molecular lattice - Held in place by weak intermolecular forces and the atoms within each molecule are bonded together strongly by covalent bonds

Question 41

Why do simple molecular substances have low melting and boiling points?

Answer 41

- Not much energy is needed to overcome the weak intermolecular forces between molecules - Can be broken even by energy present at low temps. - Covalent bonds = strong and DO NOT break

Question 42

What is the solubility of non-polar simple molecular substances?

Answer 42

Non- polar solvent: intermolecular forces form between molecules in lattice + solvent which weakens the forces present in the simple molecular lattice, causing them to break and therefore the compound dissolves since the lattice breaks down. Polar solvent: LITTLE interaction between molecules in the lattice and solvent, and the intermolecular forces are very strong in a polar solvent (more Van der Waals). the lattice doesn't break down.

Question 43

What is the solubility of polar simple molecular substances?

Answer 43

May dissolve in POLAR SOLVENTS as the polar solute molecules and polar solvent molecules can attract eachother. Some compounds may be hard to predict. E.g. overall ETHANOL is POLAR but it has polar and non-polar parts so it can dissolve in polar + non polar solvents. Some biological molecules have hydrophilic (e.g. OH) and hydrophobic (C-H carbon chain) parts.

Question 44

What is the electrical conductivity of simple molecular substances?

Answer 44

- No mobile charged particles = no electricity