Atomic Structure,Bonding, energetics Flashcards
Isotopes
Isotopes are atoms of the same element with a different no. of neutrons
- chemical properties of isotopes are similar
- physical properties are different (due to mass - changes BP & MP)
proof of electron orbitals
- Drop of ionisation energy between G5 & G6 is proof of electron orbitals.
- Oxygen has a lower IE than nitrogen
- There’s no difference between atomic radius & shielding, but there is more repulsion between a pair of electrons within an orbital so electrons in shared orbitals are easier to move.
Time Of Flight (TOF) mass spectrometry processs
1 - IONISATION
↳ vaporised gas is ionised via electrospray or electron
impact
2 - ACCELERATION
↳ The ions are accelerated by an electric field. (relies on particles being charged)
↳ all ions will have the same KE (velocity dependent on
mass)
3 - ION DRIFT
↳ ions drift through the chamber at different speeds under no electric field
4 - DETECTION
↳ Ions are detected by producing current on detection plate which creates a mass spectrum.
Trend in Ionisation energy across a period
- ↑Nuclear charge across period ∵ increase in atomic no.
- ↓ Atomic Radius
↳ atomic radius decreases slightly due to greater nuclear charge that pulls outer electrons closer - NO change in shielding effect ∵ same no. of electron shells
Trend in Ionisation energy across a group
- ↑ Atomic Radius
↳ greater distance between nucleus and outermost electron, decreased attraction. - ↑ Shielding effect
↳ greater no. of inner shells, ∴ greater repulsion so decreased attraction. - negligible nuclear charge increase
Factors affecting IE
Shielding -
The repulsion of an electron from inner shell electrons.
- more inner shells present, lower IE
Atomic Radius -
↑ atomic radius, lower IE, outer electron further from nucleus so weaker attractive pull from nucleus.
Nuclear Charge -
higher nuclear charge the higher the ionisation energy, stronger attraction to outer electrons.
How is Electrospray Ionisation done?
Sample is dissolved in solvent
- High voltage is applied
- High voltage removes proton from solvent and attaches it to sample
- X(g) —> XH⁺(g)
How is Electron Impact Ionisation performed
- Sample is vaporised
- Hit with electrons from electron gun
- The electrons knock off electrons from the molecule
- X —-> X⁺+ e⁻
(often causes fragmentation)
Electron Configuration of Transition Metals
1s²2s²2p⁶3s²3p⁶4s¹3d⁵ <— Chromium
1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰ <—- Copper
+ When forming ions they lose their 4s electron first
Proof of electron sub-shells
- Drop of ionisation energy between G2 & G3 is proof of sub-shells.
- Beryllium has a greater ionisation energy than boron.
- Boron’s outer electron occupies a 2p sub-shell which increases atomic radius & it’s electron experiences more shielding from inner electrons ( both 1s² and 2s²electrons shield it)
Properties of Water
- Significantly higher boiling point than other hydrides
- Surface tension ( how strongly molecules are held to the structure of a liquid)
- H bonds exert a downwards force
- High Viscosity
- Density of ice lower than water because it freezes into regular lattice
structure that are further apart so more open structure =
less dense - solvent can dissolve simple alcohols and ionic compounds
Physical Properties of Metallic Structures
- Metals have high boiling & Melting points
- More delocalised electrons present, the higher the melting point of the metal.
- because greater electrostatic attraction so stronger bond
- Good conductors of heat & electricity because of delocalised electronns
- insoluble unless liquid metal.
Charge Clouds
- region where there is a high chance of an electron pair being present. / region of negative charge.
- Can contain either boning pairs or lone pairs
- Lone pair electron charge clouds repel more than bonding pair clouds
Great repulsion LONE - LONE
LONE - BOND
BOND - BOND
Lowest repulsion
<- VSEPR theory
Formation of temporary dipoles
Temporary dipoles are week intermolecular forces
- When two atoms come towards each other the electron CLOUDS repel each other
- causes sudden displacement of electrons to one side resulting in a temporary dipole.
- dipoles are constantly being created or destroyed.
ALL shapes of molecules: name,shapes & angles
Factors affecting the strength of a metallic bond
- size of positive charge on the ions
- greater charge =greater attraction to delocalised electrons
- Size of Metal Ion
- strength of metallic bond increases with decreasing metal
ion size - shorter distance between positive nucleus and delocalised
electrons.
- strength of metallic bond increases with decreasing metal
- Number of mobile electrons per atom
- more mobile electrons contributing to the sea of electrons
holding lattice together
- more mobile electrons contributing to the sea of electrons
Graphite
- Organised sheets of hexagons held together by Van Der Waals inbetween them
- the layers can easily slide over each other because there is only weak intermolecular forces holding them together.
-good dry lubricant
Bond Enthalpy
- Energy required to break one mole of a particular covalent
bond in gaseous state - The Bond Energy depends on Bond Length
- the shorter the bond length, the stronger the bond . thus
more energy is needed to break it.
- the shorter the bond length, the stronger the bond . thus
- Lower Bond Energy –> more reactive
Hydrogen bonding
Polar bond - H” F,N,O’
- Hydrogen has a high charge density (only 1 shell) so the “ hydrogen can be attracted by lone pairs of nearby N,O,F molecules
+ due to hydrogen bonding it means HF is the hydrogen halide with the highest boiling point.
Explain why the third ionisation energy of magnesium is much higher than the second ionisation energy of magnesium.
The electron is removed from lower energy level
- electron being removed is less shielded so more energy is needed to overcome attraction.
Enthalpy of Formation (ΔH°f)
The enthalpy change when one mole of a substance is produced from its elements under standard conditions.
Hess’s Law
The Enthalpy change is independent of the route taken.
Enthalpy of Combustion (ΔH°c)
The enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions.
Bond Enthalpy
The energy required to break one mole of the stated bond in a gaseous state, under standard conditions.
How is the relative abundance of a molecule determined using a TOF mass spectrometer
At he detector/negative plate the ions GAIN an electron, causing a current
The relative abundance depends on the SIZE of the current.
Why do isotopes have the same chemical properties?
Same electron configuration so there is no change in chemical properties
Relative Atomic Mass
Average/mean of 1 atom of an element 1/12 mass of one atom of carbon-12
Which is larger Na+ or F- and why?
- F-
- both Na+ and F- have same electron arrangement
- sodium ion has more protons so attracts outer electrons closer/stronger attraction to outer electrons.
Why does SiO2 have a larger boiling point than P4O10?
-SiO2 is macromolecular/ giant covalent
-therefore it has strong covalent bonds which require a lot of energy to overcome.
-P4O10 is simple molecular so only has Vander Waals forces acting between the molecules.
Define enthalpy change
The change in heat energy during a reaction at constant pressure.
why may a bond not have a mean bond enthalpy
it may be the only bond in the substance/reaction
why may the experimental value for enthalpy of combustion be less than the data book value?
- heat loss to the surroundings
-incomplete combustion
Standard enthalpy of combustion
The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions.
Why many a calorimeter heat change calculation not equal the enthalpy change?
the pressure in a calorimeter is not constant
find the heat energy change using calorimeters in an efficient way
- insulate beaker using a polystyrene cup to reduce heat loss
- record the temperature by for a suitable time before adding the substance (if a solution) to establish an accurate initial temperature
- record the temperature values at regular time intervals and plot the temperature results against time on a graph
- extrapolate the graph to find your theoretical maximum temperature
