Atomic structure and bonding Flashcards
What is an atom?
The smallest particle of a chemical element
Ionisation Energy
The amount of energy needed to remove 1 mole of electrons from a mole of atoms, in the gaseous state
Factors that affect ionisation energy
Nuclear charge, shielding and distance from nucleus
Successive ionisation energies
The energy required to remove each electron in turn
What can a mass spectrometer be used for?
To find the relative abundance and mass/charge ratio of an element or compound
Why is the mass spectrometer a vacuum?
Prevent any particles being tested from colliding with molecules in the air
What is electrospray ionisation?
Sample dissolved in a volatile substance
Injected through a fine hypodermic needle
The tip of the needle is connected to the positive terminal of a high voltage power supply
The particles gain a proton and are ionised
What is electron impact ionisation?
The sample is vaporised
High energy electrons are fired at it from an electron gun
This will knock off an electron from each particle to form a positive ion
What is acceleration in a mass spectrometer?
Positive ions are attracted towards a negatively charged plate and accelerate towards it
Once accelerated, all ions have the same kinetic energy
The amount they accelerate depends on the mass to charge ratio of an ion
What is ion drift in a mass spectrometer?
Particles travel at different speeds due to their mass and start to drift apart
How are ions detected in a mass spectrometer?
Ions hit the detector and gain electrons which generates a current
The size of the current is proportional to the abundance of the ion
Why are sample particles ionised?
So they can be accelerated towards a negatively charged plate and gain electrons to generate a current when they hit the detector
How are ions accelerated in a mass spectrometer?
Positive ions attracted to negatively charged plate
All ions have the same kinetic energy
How are ions separated in a mass spectrometer?
Ions travelling at higher speeds (slower m/z ratio) move ahead of those travelling more slowly (large m/z ratio)
What is the relative atomic mass?
Average weighted mass of an atom relative to carbon 12
What is electronegativity?
The power of an atom to attract the pair of electrons in a covalent bond
How to work out if a molecule is polar?
Partial charges around the molecule change
So, asymmetrical
Dipoles do not cancel out
Permanent dipole
Polar
How to work out if a molecule is non-polar?
Partial charges around the molecule remain the same
So, symmetrical
Dipoles cancel out
No permanent dipole
Non-polar
How does hydrogen bonding arise?
Large difference in electronegativity between the oxygen atom and the hydrogen atom of the OH bond
This polarises the OH bond
There is a strong attraction between the lone pair of Oxygen atom and partially positive hydrogen atom on another molecule
How do permanent dipole-dipole forces arise?
There is a difference in electronegativity between the chlorine atom and hydrogen atom
This polarises the HCL bond forming a dipole
The dipoles do not cancel out as the molecule is asymmetrical
There is an attraction between the partial positive hydrogen atom and partial negative chlorine on another molecule
How do induced dipole-dipole forces arise?
Random movement of electrons in a molecule causes an uneven distribution of electrons
This forms a temporary dipole
This induces a dipole in another molecule
There is an attraction between dipoles on neighbouring molecules
What are the 4 properties of metals and why?
Good conductors of heat because delocalised electrons help transfer energy through the metal efficiently
Good conductors of electricity because delocalised electron can flow easily
Strong - strong electrostatic attraction between positive metal ions and delocalised electron
Malleable and ductile - rows of metal ions can slide past one another
High melting and point
What is ionic bonding?
Strong electrostatic attraction between oppositely charged ions
What is a covalent bond?
Shared pair of electrons between 2 atoms
What is a coordinate bond?
Shaired pair of electrons with both electrons supplied by one atom
What is ionic bonding?
Electrostatic attraction between oppositely charged ions in a lattice
What is metallic bonding?
Attraction between positive metal ion and delocalised electrons arranged in a lattice
What are macromolecular structures?
Covalent bonds extend throughout the entire structure
What are the macromolecular structures?
Carbon
Silicon
Silicon oxide/dioxide
Example of macromolecular crystals
Diamond
Graphite
What are allotropes?
Different structural forms of the same element
Describe the structure of a diamond
Each carbon has 4 covalent bonds
Tetrahedral shape repeated over the whole structure
High melting and boiling point
Non-conductors - no delocalised electron
Describe the structure of graphite
Layers with 3 covalent bonds to each carbon
Each carbon has a delocalised electron - conducts electricity
Layers held together by weak intermolecular forces
Layers are far apart in comparison to covalent bond length - low density
Soft layers can slide over each other
High melting point
What are simple molecular structures?
Made up of molecules
Example of simple molecular structures
Iodine
NH3
H2O
Describe the structure of iodine
Diatomic molecule with a single covalent bond
Solid iodine crystals are made up of a lattice of these I2 molecules
Each I2 molecule is held close to its neighbouring molecule by intermolecular forces
Describe the strength of repulsion
Strongest: lone pair - lone pair
Lone pair - bond pair
Weakest: bond pair - bond pair
What does electronegativity mean?
Power of an atom to attract the pair of electrons in a covalent bond
What does polarity mean?
Unequal sharing of electrons between 2 atoms covalently bonded
Explain the importance of hydrogen bonding in ice
Ice is less dense than water
Because the hydrogen bonds hold the molecules further apart
Why is the boiling point of aluminium higher than silicon but the melting point of silicon is higher?
Silicon, once molten, only a little more energy is needed to vaporise it so the melting point of silicon is higher than its boiling point
Whereas, aluminium once molten a lot of energy is still needed to overcome strong electrostatic metallic bonds so aluminium has a high boiling point
Suggest why magnesium is a liquid over a much greater temperature range compared to bromine
Liquid Mg has strong electrostatic attractions between delocalised electrons and metal ions which still require a lot of energy to break
Why does I2 have a higher boiling point than HCl
Iodine has more electrons than HCl
Greater energy required to overcome the Van Der Waals in I2
Identify the s-block metal that has the highest first ionisation energy
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