Flashcards in EL Deck (30):
Relative atomic mass
average mass of an atom of an element compared to 1/12 the mass of a C-12 atom.
Relative isotopic mass
mass of an atom of an isotope compared to 1/12 the mass of a C-12 atom.
Relative formula mass/ relative molecular mass
average mass of a molecule or formula unit compared to 1/12 of C-12.
6.02 x 10^23, the number of particles in 12 g of C-12.
Ar can be worked out using mass spec.
shape of s and p orbitals
How many electrons can occupy a single orbital?
Equation linking energy and frequency
Energy (J) = Planck’s constant (...) x frequency (Hz)
How are elements in the periodic table ordered?
in order of atomic/ proton number
How are elements in the same group of the periodic table similar?
have the same number of electrons in their outer shell so similar chemical properties.
Similarities between absorption and emission spectra
- Both line spectra
- Lines at same positions for a given element
- Lines become closer together at higher frequencies
- Lines represent electronic transitions to or from a particular energy level.
Differences between absorption and emission spectra
- Absorption: black lines on a coloured background
- Emission - coloured lines on a black background.
How do absorption spectra arise?
Electrons in their ground state can absorb energy at discrete frequencies and transition to a higher energy level - an excited state. The frequencies of radiation absorbed correspond to the differences between energy levels as E=hv. These frequencies are missing on an absorption spectrum - they are shown as black lines.
How do emission spectra arise?
Electrons can release energy by dropping from a higher to a lower energy level. Energy is released at specific frequencies because energy levels are quantised and is shown as coloured lines on a black background on an emission spectrum.
First ionisation enthalpy definition
the amount of energy required to remove 1 electron from each atom in 1 mole of gaseous atoms, to form 1 mole of gaseous 1+ ions.
First ionisation enthalpy general equation
X(g) ⇒ X+(g) + e-
what 3 factors does first ionisation enthalpy depend on?
Atomic radius, nuclear charge and electron shielding
Describe and explain the trends in first ionisation enthalpy across a period.
Across a period, IE increases because electrons in the same shell, which are the same distance from the nucleus and experience the same shielding and more strongly attracted to the nucleus by the greater number of protons present. More energy is required to remove an electron
Describe and explain the trends in first ionisation enthalpy down a group.
Down a group, first IE decreases as there is less attraction between the nucleus and outer e-. This is because outer e- are further from the nucleus and experience more shielding.
Describe and explain the relative reactivities of s block and p block metals in terms of ionisation enthalpies.
S- block metals are more reactive than p- block metals in the same period because they have a lower nuclear charge so valence electrons are less strongly attracted so IEs are lower and outer electrons are lost more readily than from p- block metals.
Reaction of a group 2 metal and oxygen
2M + O2 ⇒ 2MO
A metal oxide is produced.
Reaction of a group 2 metal and water
M + 2H2O ⇒ M(OH)2 + H2
A metal hydroxide and hydrogen gas are produced.
How and why are the first ionisation enthalpies of groups 2 and 3 elements different?
This is why first ionisation enthalpies for period 3 elements are lower than for the period 2 element in the same group.
How does the reactivity of group 2 metals and water/ oxygen change down the group and why?
Reactivity increases down the group because the outer electrons are further from the nucleus, so are less strongly attracted and are more readily lost.
Why are group 2 oxides and hydroxides basic?
(do not need to give reactions)
Oxides react with water to form the metal hydroxide.
Metal hydroxides dissolve in water and dissociate to form OH- ions, so making to solution alkaline.
Reactions of group 2 metal oxides and hydroxides with water
MO + H2O ⇒ M2+ + 2OH-
M(OH)2 ⇒ M2+ + 2OH-
Equations for the reaction of a group 2 oxide or hydroxide with hydrochloric acid
MO + 2HCl ⇒ MCl2 + H2O
M(OH)2 + 2HCl ⇒ MCl2 + 2 H2O
Solubility trend of group 2 hydroxide
increases down the group
Mg(OH)2 is insoluble.
Solubility trend of group 2 carbonate
decreases down the group.
Thermal stability of group 2 carbonate - trend down the group
increases down the group - higher temperature is required for decomposition to occur.