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OCR Chemistry A Level Module 2 Foundations in Chemistry > 2.2. Electrons, Structure and Bonding > Flashcards

2.2. Electrons, Structure and Bonding Flashcards

1
Q

How many electrons can fill the first 4 shells?

A

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

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

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2
Q

What are atomic orbitals?

A

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

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3
Q

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

A

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

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4
Q

what is the shape of s orbitals?

A

Sphere

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5
Q

what are the shapes of p orbitals?

A

Dumbbells on y, x and z axis

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6
Q

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

A

s = 2
p = 6
d = 10

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7
Q

What property do electrons have?

A
  • SPIN, so they are shown as arrows. Any 2 electrons sharing an orbital will have opposite spins.
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8
Q

Write the electron configuration of krypton (36 e-)

A

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

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9
Q

What is the shorthand configuration for krypton?

A
  • 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

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10
Q

What are the 2 exceptions?

A

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.

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11
Q

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

A
  • 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.

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12
Q

What is ionic bonding?

A

strong electrostatic attraction between positive and negative ions

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13
Q

What is the structure of ionic compounds?

A
  • GIANT ionic lattice
  • Repeating pattern of ions where each ion attracts oppositely charged ions in all directions
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14
Q

What is a property of ionic compounds? 1. MP

A

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

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15
Q

What is a property of ionic compounds? 2. Solubility

A

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.

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16
Q

What is a property of ionic compounds? 3. Conductivity

A

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.

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17
Q

what is a covalent bond?

A

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.

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18
Q

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

A

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

19
Q

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

A

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

  • The number of bonds that can be made depends on valence electrons
20
Q

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

A

Predictions cannot always be based on noble gas structures.

21
Q

What is the case with boron?

A
  • 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.
22
Q

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

A
  • 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.
23
Q

What are double covalent bonds? What are some examples?

A
  • 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

24
Q

WHat are triple covalent bonds? What are some examples?

A
  • 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

25
Q

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

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

NH4+

26
Q

what is electronegativity?

A
  • the ability of an atom to attract a pair of electrons in a covalent bond
27
Q

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

A
  • pauling scale
28
Q

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

A
  • 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.
29
Q

What is a covalent bond?

A

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

30
Q

What occurs in a non polar bond?

A

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

31
Q

What happens in a polar covalent bond?

A

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)

32
Q

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

A

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.

33
Q

How do ionic compounds dissolve in polar solvents?

A

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

34
Q

What are intermolecular forces?

A
  • weak interactions between dipoles of different molecules
  • largely responsible for physical properties
35
Q

How are induced dipole-dipole interactions formed?

A
  • 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
36
Q

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

A
  • more electrons in each molecule = stronger London forces between molecules = more energy needed to overcome them = increased boiling point
37
Q

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

A
  • 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.
38
Q

What is hydrogen bonding? How does it occur?

A

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.

39
Q

What are some anomalous properties of water?

A

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.

40
Q

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

A
  • 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
41
Q

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

A
  • 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
42
Q

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

A

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.

43
Q

What is the solubility of polar simple molecular substances?

A

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.

44
Q

What is the electrical conductivity of simple molecular substances?

A
  • No mobile charged particles = no electricity

OCR Chemistry A Level Module 2 Foundations in Chemistry (2 decks)

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