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AS Chemistry > 2.2 > Flashcards

2.2 Flashcards

1
Q

Describe an S orbital

A

•spherical in shape not circular
•each can accommodate 2 electrons with opposite spins at any time
O

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2
Q

Describe a P orbital

A
  • 3D dumbbell shape with centre at nucleus
  • 3 different P orbitals
  • each P orbital can accommodate 2 elections with opposite spins - so there are a maximum of 6 electrons in a shell
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3
Q

List the maximum electrons per shell

A 
1st shell - 2
2nd shell - 8
3rd shell - 18
4th shell - 32
5th shell - 50
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4
Q

What is an orbital

A

An orbital is a region in space where one is likely to find 2 elections. Orbitals can hold up to 2 electrons as long as they have opposite spinning directions. Orbitals have different shapes (S, P, D, F)

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5
Q

How often does a S orbital occur in an electron

A

One in every level

- holds 2 electrons

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6
Q

How often does a P orbital occur in an electron

A

3 in levels from 2 upwards

- holds 6 electrons (2 in each kind of orbital)

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7
Q

How often does a D orbital occur in an electron

A

5 in levels from 3 upwards

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8
Q

How often does a F orbital occur in an electron

A

7 in levels from 4 upwards

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9
Q

Describe the different types of bonds.

A 
Chemical:
Ionic
Covalent
Dative covalent (or co-ordinate)
Metallic 
Physical:
Induced dipole-dipole interaction (weakest)
Permanent dipole-dipole interaction
Hydrogen bonds (strongest)
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10
Q

Describe the formation of ions.

A

Positive ions:

  • Also knows as cations, they are smaller that the original atom
  • Formed when an electron is remove from an atom

Negative ions:

  • Also known as anions, they are larger than the original atom due to electron repulsion in the outer shell
  • Formed when electrons are added to atoms
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11
Q

How are orbitals filled up?

A

Orbitals are not filled in numerical order because the principal energy level gets closer together as you get further from the nucleus.

This results in overlap of sub levels.

The first example occurs when the 4s orbital is filled before the 3d orbitals.

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12
Q

What is the filling order of orbitals?

A 
1s 
2s
2p
3s
3p
4s 
3d
4p
5s
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13
Q

What two elements have different configurations to the other elements?

A

Chromium + Copper, the 4s orbitals are not full whilst the 3d orbitals are.

This is because the atoms are more stable like this.

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14
Q

What is a ionic bond?

A

An ionic bond is an electrostatic attraction between two oppositely charged ( + and - ) ions

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15
Q

How do you get an ionic compound?

A

When oppositely charged ions form an ionic bond, you get an ionic compound.

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16
Q

What do dot-and-cross diagrams show?

A

Dot-and-Cross diagrams show where the electrons in a bond come from

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17
Q

Describe sodium chloride

A 
Sodium chloride (NaCl)
•Giant lattice structure - same basic unit repeated
•Forms as each ion is electrostatically in all directions to ions of opposite charge
•Cubed shaped (different ionic lattices - different shapes)
•Very strong ionic bonds, takes lots of energy to break, very high boiling point
18
Q

Describe the physical properties of ionic compounds due to ionic structure

A
  • Ionic compounds conduct electricity when molten/dissolved - ions in a liquid are mobile & can carry a charge
  • High melting & boiling points - strong electrostatic forces
  • Ionic compounds tend to dissolve in water - water molecules are polar & attracted to charged ions, they pull the ions away from lattice & cause it to dissolve
19
Q

What is a covalent bond?

A

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

•This occurs between non-metals in order to achieve a full outer shell

20
Q

How is the strength of a covalent bond shown?

A

The strength of a covalent bond is shown by its average bond enthalpy. This measures energy required to break a covalent bond.
Stronger bond = more energy = greater average bond enthalpy value

21
Q

What is dative covalent bonding?

A

Dative covalent bonding is where both electrons come from one atom.

22
Q

Why are covalent bonds very strong?

A

Covalent bonds are very strong because of the electrostatic forces between the shared negatively charged electrons and the positively charges protons in the nucleus.

23
Q

What is the electron repulsion theory?

A

The shape adopted by a single molecule/ion that allows all the pairs of electrons to be as far away as possible.

24
Q

What is the shape and bond angles of the molecule that has 1 or 2 bond pairs?

A

Linear

180°

25
Q

What is the shape of the molecule that has 3 bond pairs?

A

Trigonal planar

120°

26
Q

What is the shape of the molecule that has 4 bond pairs?

A

Tetrahedral

109.5°

27
Q

What is the shape of the molecule that has 5 bond pairs?

A

Trigonometry bipyramidal

120° / 90°

28
Q

What is the shape of the molecule that has 6 bond pairs?

A

Octahedral

90°

29
Q

Why are there exceptions to the shape rule (linear, trigonal planar etc.)? + examples

A

A lone pair of electrons is slightly more electron-dense than a bonded pair
•Lone pairs cause extra repulsion

Strength order:
Lone pair/lone pair > bonded pair/lone pair > bonded pair/bonded pair

E.g:
NH3 (Ammonia) 107°
CH4 (Methane) 109.5°
H2O 104.5°

30
Q

What is electronegativity?

A

The ability of an atom to attract the pair of electrons in a covalent bond to itself.
•Electronegativity increases across periods and decreases down a group
-Fluorine is the most electronegative element
•Measure on the Pauling scale - the greater an element’s Pauling value, the higher it’s electronegativity.

31
Q

What are physical forces?

A

The forces between different molecules within a substance (intermolecular forces).

32
Q

What are the different types of intermolecular forces?

A 
3 different types:
Induced dipole-dipole interactions (weakest)
Permanent dipole-dipole interactions
Hydrogen bonds (strongest)
33
Q

Describe induced dipole-dipole interactions

A
  • At any instance in time, it is possible that more electrons will lie to one side of the atom/molecule that the other
  • An instantaneous/temporary dipole is produced
  • This induced a weak dipole in nearby molecules/atoms - creates weak forces
  • Boiling point increases as the size of the molecule/atom increases - more electrons so size of induced dipole-dipole interaction forces increases
34
Q

Describe permanent dipole-dipole interactions

A

Polar molecules form permanent dipole-dipole interactions - the weak δ- and δ+ charges on polar molecules cause weak electrostatic forces of attraction between molecules - permanent dipole-dipole interactions (happens in addition to induced dipole-dipole interactions, not instead of)

35
Q

How do polar covalent bonds form?

A

Electrons spend more time nearer to one of the bonded atoms - said atom gains a small negative charge - other atom gains a small positive charge - this produces a polar covalent bond

36
Q

How do you get non-polar atoms?

A

Similar atoms have similar electronegativity so molecules will be non-polar

37
Q

How is a polar molecule created?

A

When there is a difference in electronegativity

  • Difference in polarity is called a dipole
  • A bigger difference in electronegativity between 2 atoms will cause a greater degree of bond polarity

Some molecules are polar if they contain polar bonds.

  • The molecules will be polar if they have a net dipole movement- a bit like balanced forces
  • Molecules are polar if they contain polar bonds and are asymmetric
38
Q

Do covalent bonds break when you melt or boil things?

A

No (except for giant molecular substances like diamond) as to melt/boil a simple covalent compound you only have to overcome the intermolecular forces that hold the molecules together.
You don’t need to break the (stronger) covalent bonds that hold the atoms together in the molecules (which is why simple covalent compounds have relatively low melting + boiling points.

E.g when you boil water you get steam, not hydrogen and oxygen

39
Q

Describe hydrogen bonding

A
  • Strongest intermolecular force
  • Can only happen when H is covalently bonded to fluorine, nitrogen or oxygen (all very electronegative)
  • H - high charge density
  • Bond is very polarised so a weak bond forms between the H of one molecule and a lone pair of electrons on the F, N or O in a other molecule.
  • Molecules which have H bonding usually contain -OH or -NH groups
40
Q

What is the effect of hydrogen bonding on a substance?

A
  • Water, ammonia and hydrogen fluoride have high melting+boiling points compared to other hydrides in their group due to the extra energy needed to break the hydrogen bonds
  • Ice - H2O molecules held together in a lattice by hydrogen bonds - ice melts, hydrogen bonds broken, SO ice has more H bonds than liquid water, H bonds are relatively long, this makes ice less dense than water
41
Q

Describe the trends in boiling points with intermolecular forces

A

•Main factor determining boiling point is strength of induced dipole-dipole forces (unless molecule can form H bonds)

  • explains why the boiling points of group 7 hydrides increase from HCl to HI
  • although permanent dipole-dipole interactions are decreasing, the number of electrons in the molecule increases, so the strength of the induced dipole-dipole interactions also increases
  • BUT if you have two molecules with a similar no. Of electrons their strength of induced dipole-dipole interactions will be similar
  • so if one of the substances has molecules that are more polar than the other it will have stronger permanent dipole-dipole interactions
  • so a higher boiling point
42
Q

Describe the trends with simple covalent compounds

A

•Low melting + boiling points
-intermolecular forces weak - not much energy needed to break them
-often liquids + gases at room temp
•Polar molecules are soluble in water
-water - polar molecule - tends to dissolve other polar substances
-compounds with H bonds can form H bonds with water molecules - will be soluble
-Molecules that only have induced dipole-dipole forces - insoluble
•Don’t conduct electricity
-Overall covalent molecules are uncharged
-means they can’t conduct electricity

AS Chemistry (8 decks)

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