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Chemistry Scholarship > C3.4 > Flashcards

C3.4 Flashcards

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1
Q

In what order do an atom’s subshells increase?

A

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6…

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2
Q

What are the two exceptions to subshell categorizing? Why?

A

Copper and Chromium as they only have one electron in their 4s shell.

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3
Q

What is ionisation energy?

A

The amount of energy required (kJ) to remove an electron from each of one mole of atoms or ions in the gas phase.

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4
Q

What is the trend in ionisation energy? Why?

A

Ionisation increases across a period and decreases down a group. Increases across a period as there are more protons in nucleus so greater nuclear charge. Decreases down a group as there are more shells shielding valence electrons from shells.

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5
Q

Why does ionisation energy drop from Be to B and Mg to Al?

A

A new shell is formed and so the valence electrons are less shielded.

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6
Q

How do we know when a valence shell has been stripped of electrons on an atom’s ionisation graph?

A

A large jump in energy required will be evident. - shells are closer so more electrons attracted by protons.

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7
Q

How is the atomic radius of an atom determined?

A

Two of the same atoms are touched (eg. covelently bonded), the distance from edge to edge is measured and halved.

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8
Q

What is the trend in atomic radius?

A

It decreases across a period (as electrons are pulled closer by greater nuclear charge) and increases down a group (as more shells so valence electrons further away)

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9
Q

Why do the noble gasses not have definite radii?

A

They do not bond (as they are stable) so their radii are unknown

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10
Q

What are the trends in ionic radii?

A

Positive ions smaller than negative ions as + have more protons:electrons so are more attracted.

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11
Q

What are the trends in electronegativity?

A

Electronegativity increases across a period and up a group. F is highest.

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12
Q

What is electronegativity?

A

The relative tendency of an atom to attract a pair of bonding electrons.

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13
Q

What are the steps for drawing a lewis structure?

A
  1. Work out total VALENCE electrons
  2. Draw skeleton
  3. Add electrons so that all are full.
    NOTE 1: If it is an ion, add or subtract electrons for negative or positive charges.
    NOTE 2: Some elements (Xe, P) can have expanded octets where they can hold more than 8 electrons.
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14
Q

Where can Hydrogen Bonds form?

A

Between molecules with Hydrogen and those with electron pairs. Eg. H-O, H-N etc.

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15
Q

What makes a molecule polar?

A

If the electronegativity difference between atoms in a molecule is asymmetrical.

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16
Q

What happens when a molecule is polar?

A

Some atoms will have negative dipole if they have high electronegativity, while some will have a positive dipole if they have low electronegativity.

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17
Q

What are the intermolecular forces in order of strength?

A 
Temporary dipoles (weakest)
Permanent dipoles (stronger)
Hydrogen bonds (strongest)
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18
Q

What are van der waals forces (temporary dipoles)?

A
  • They occur due to long range attraction between protons and electrons in adjacent atoms/molecules.
  • The forces are very weak.
  • The larger the molecule, the more electrons and protons there are so the stronger the forces will be.
  • Common to stable atoms/molecules
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19
Q

What are permanent dipole forces?

A
  • Forces between the dipoles of polar molecules
  • Due to uneven electron distribution the positive ends of one molecule will be attracted to the negative ends of others.
20
Q

What is hydrogen bonding?

A

Extremely strong bonds between Hydrogen and a lone pair of electrons.
For this to happen the hydrogen must be bonded to a very electronegative element, eg. F, O, N. This causes the electron to be pulled almost completely from the atom, exposing a nearly bare proton.

21
Q

What affects the energy needed to break bonds?

A

The stronger and more forces between molecules, the more energy is needed.

22
Q

Which bonds are being broken when molecular substances are melted, dissolved, boiled etc.?

A

Intermolecular bonds only- intra have much higher breaking points.

23
Q

What is the formula for measuring the enthalpy of a reaction?

A

ΔrH = H(products) - H(reactants) Where H is enthalpy.

24
Q

Which way does the graph go for an exothermic reaction?

A

Reactants is higher than products.

25
Q

Which way does the graph go for an endothermic reaction?

A

Products is higher than reactants

26
Q

What is entropy?

A

The measure of the disorder or randomness of a system, dependent on temperature.

27
Q

What characterizes high entropy?

A

Great freedom to move randomly (eg. gasses being vaporised)

28
Q

What characterizes low entropy?

A

Limited freedom to more randomly (eg. solids)

29
Q

What are some ways to increase entropy?

A
  • Dissolving a substance into water
  • Increasing the amount of a substance on the reactant side- more particles to move about.
  • Increasing the temperature.
30
Q

When will a reaction always be spontaneous?

A

When the reaction is exothermic and gains entropy.

31
Q

When will a reaction always be non-spontaneous?

A

When the reaction is endothermic and decreases entropy.

32
Q

When may a reaction be spontaneous?

A
  • A drop in entropy and exothermic

- An increase in entropy and endothermic.

33
Q

What is a thermochemical equation?

A

A fully balanced chemical equation for the reaction plus an indication of heat released or absorbed.

34
Q

What is Heat for Combustion ΔcH?

A

The enthalpy change when one mole of a substance is burnt completely with all reactants and products in their standard states.

35
Q

What is Heat of Formation ΔfH?

A

The enthalpy change when one mole of a substance is formed from its elements with all reactants and products in their standard states.

36
Q

What is a standard state?

A

When they are at 25 degrees and 1 atmospheric pressure.

37
Q

What is the ΔfH for elements?

A

Zero

38
Q

What are different intramolecular forces?

A

Metallic
Covalent
Ionic
Covalent Network

39
Q

Where are the weakest intramolecular forces found?

A

Between atoms of a noble gas

40
Q

What is ΔfusH?

A

The energy needed to change one mole of a substance from a solid to a liquid at its melting point.

41
Q

What is ΔvapH?

A

The energy needed to change one mole of a substance from a liquid to a gas at its boiling point.

42
Q

What are the steps to find the ΔrH of a reaction with multiple reactions for both products and reactants?

A
  1. State problem as an equation and write equations for all given data
  2. If necessary, reverse reactions (other than unknown) or multiply them by coefficients to match the overall equation.
43
Q

What is bond energy?

A

The energy per mole needed to separate the two atoms forming a bond providing reactants and products are in the gaseous state.

44
Q

What are uses of bond energies

A
  • Comparing the strengths of bonds
  • Understanding structure and bonding
  • Estimating the enthalpy changes in reactions
  • Underestmating the mechanisms of chemical reactions
45
Q

What is the way to remember enthalpy of bonds broken/formed

A

Bonds broken= positive = BP

Bonds made = negative = mn

Chemistry Scholarship (4 decks)

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