Chemical Changes and Structure Flashcards
What is Ionisation energy?
First ionisation energy is the energy required to remove 1 mole of electrons from 1 mole of gaseous atoms
2nd and subsequent ionisation energies are energies required to remove further moles of electrons.
What happens to Covalent Radius when you move down a group?
The covalent radius increases as the number of occupied electron shells increases, which increases shielding.
What happens to covalent radius when you move across a period?
The covalent radius decreases because of the increase in nuclear charge ( increase in atomic number ) attracts electrons more strongly.
What happens to electronegativity when you move across a period?
Electronegativity increases
why? - there are more protons so nuclear charge is increased.
Where are the strongest reducing agents on the electrochemical series?
The top right hand column.
Where are the strongest oxidising agents on the electrochemical series?
The bottom left hand column
What are oxidising agents used as?
They kill fungi and bacteria and break down coloured compounds.
so often used as bleach for clothe or hair (eg. hydrogen peroxide)
What are examples of oxidising and reducing agents?
Oxidising Agents = Hydrogen peroxide, dichromate and permanganate ions are group ions that are strong oxidising agents in acidic solutions.
Reducing Agents = Carbon monoxide
What are hydrogen bonds?
Hydrogen bonds are electrostatic forces of attraction between molecules that contain highly polar bonds.
they are the strongest intermolecular force.
hydrogen bonds exist between F-H, O-H, N-H
What are permanent dipole-permanent dipole interactions?
Permanent dipole - permanent dipole interactions are additional electrostatic forces of attraction between polar covalent molecules.
pd-pd interactions are stronger than LDF’s for molecules with similar numbers of electrons.
Describe Ionic bonding.
Ionic bonds are the electrostatic attractions between positive and negatives ions.
ionic compounds form lattice structures of oppositely charged ions
How does difference in electronegativity affect bonding the of an atom?
No difference = Pure covalent bond
Small difference = Polar covalent bond
Large difference = Ionic bond
What are London Dispersion Forces?
LDF’s are forces of attraction that operate between all atoms and molecules. they are the weakest type of intermolecular force.
they are formed as a result of electrostatic attraction between temporary dipoles and induces dipoles caused by movement of electrons in atoms and molecules
What is the strength of London Dispersion Forces affected by?
The number of electrons within an atom or molecule
size of the molecule
What is a pure covalent bond?
In a covalent bond, atoms share pairs of electrons. the covalent bond is a result of 2 positive nuclei being held together by their common attraction for the shared pair of electrons.
What is covalent radius?
It is half the distance between the nuclei of 2 bonded atoms of the element.
It is a measure of the size of an atom.
Do elements with low electronegativities tend to act as oxidising or reducing agents?
Reducing agents as they form ions by losing electrons.
Describe the bonding of the first 20 elements.
Metallic = Li, Be, Na, Mg, Al, K, Ca
Pure covalent molecular = H2, N2, F2, O2, I2, Cl2, B2, S8, C60(fullerene)
Covalent Network = B, C (diamond/graphite), Si
Monatomic = Ar, He, Ne, Xe, Kr, Rn, Og
Describe the solubility of polar and non polar substances in polar and non polar solutions.
Ionic compounds and polar compounds tend to be soluble in polar solvents (eg water) and insoluble in non polar solvents.
Non polar molecular substances tend to be soluble in non polar solvents and insoluble in polar solvents.
What is a polar covalent bond?
Polar covalent bonds are formed when the attraction of the atoms for the pair of bonding electrons is different.
The polarity of a bond depends on the difference in electronegativity between atoms.
What is a reducing agent?
A reducing agent is a substance which donates electrons.
What is an oxidising agent?
An oxidising agent is a substance which accepts electrons.
What is electronegativity?
Electronegativity is a measure of attraction an atom in a bond has for the electrons of the bond.
What happens to electronegativity when you move down a group?
Electronegativity decreases.
why? - Atomic size increases (shells) so outer electrons are further from the positively charged nucleus.
What happens to 1st ionisation energy across a period?
It increases.
Why?
>Nuclear charge increases - electrons held more tightly so are more difficult to remove
>Additional electron goes to 2nd shell - no difference to screening effect, increased nuclear charge pulls electrons and covalent radius decreases.
>Outer electron is closer to nucleus, more strongly held so 1st ionisation energy increases
What happens to 1st ionisation energy moving down a group?
It decreases.
Why?
>Nuclear Charge increases making the outer electron harder to remove.
>Covalent radius increases, outer electron is further from the nucleus
>More inner electrons prevent outer electrons from nuclear charge, these inner electrons increasingly screen the outer electron from the nucleus. Consequently, the outer electron becomes easier to remove as the atom gets bigger, i.e. the first ionisation energy decreases on going down a group.
What groups are the strongest oxidising and reducing agents in?
Strongest Oxidising = Group 1, Alkali Metals
Strongest Reducing = Group 7, Halogens
