Atoms and bonding Flashcards
What is an absorption spectra?
This is the lack wavelengths measured from a light source because the photons of those wavelengths has been absorbed by atoms
What happens when a photon is absorbed
> Electrons absorb photons
This gives the electrons more energy and so move to a higher energy level (higher shell)
This causes these photons to not be seen on an absorption spectra
What is an emission spectra?
This is spectra produced when the photons are emitted from atoms that had previously absorbed them
How is an emission spectra produced?
> Electrons in a higher energy level fall back down to the ground state.
The change in the energy causes a photon to be emitted and this produces and emission spectrum
What is the equation to calculate the number of electrons in a shell?
Number of electrons = 2(2L+1)
Where L = N - 1
Where N is the shell number
What are the different sub-shell shapes and what are there names?
> S - Sharp
P - Principle
D - Diffuse
F - Fundamental
What is the letter corresponding to an atom with one shell?
K
What is the letter corresponding to an atom with two shell?
L
What is the letter corresponding to an atom with three shell?
M
What is the letter corresponding to an atom with four shell?
N
What is ionic bonding?
> One atom with excess electrons will donate its electrons to an atom that is deficient.
This causes both atoms to have a full outer shell
Both atoms are oppositely charged so bond
What are the material properties of ionic bonding? (5)
> Strong > Brittle > High melting point > Soluble in polar liquids > Electrical insulators
What is covalent bonding?
> Both atoms are deficient in electrons to share them so they both have a full outer shell
This is a strong bond type
What is a bonding angle?
Bonds are negatively charged and so repel as far as possible and this can produce a bond angle. For 4 bonds the bond angle is 109.5°
What are the material properties of covalent bonding?(7)
> Strong bond > High melting point > Hard solids. Including diamond. > Non-ductile > Non-malleable > Insoluble > Non-conducting
What is metallic bonding?
> Electrons are shared between all positive nuclei
Positive charges are held together in a cloud of negative charge
The attraction between opposite charges are what holds it all together
Positive charge is closely packed together
What are the material properties of metallic bonding?(4)
> High ductility
High electrical conductivity
High thermal conductivity
Low melting point
What is mixed bonding?
> Electrons are shared unequally so the bonds are polar
What is a crystal? what are its arrangement properties?
> A 3D periodic arrangement of atoms, molecules or ions
It has periodicity
It has symmetry
Constant bond lengths
How can a crystal be mapped? describe this method
> With a lattice and a basis
A lattice is a periodic arrangements of points. Each point is equally spaced apart with a distance ‘a’
A basis is an arrangement of atoms / ions / molecules around a point on the lattice
When a basis is placed at each point on a lattice it forms a crystal
What is the coordination number?
The number of atoms next to an atom in a structure (nearest neighbours)
What is a unit cell?
> This is an area / volume of a crystal with sides of length a.
a×a×a or a×a
What is the atomic packing factor? What are the steps to calculating this?
This is the volume of a unit cell that is atom as a percentage of the volume of the whole unit cell.
Steps:
> Calculate the volume of the unit cell in terms or radii of atoms
> Calculate the volume of atoms in that uni cell, accounting for partial atoms
> ( Volume of atoms / Volume of cell ) × 100 = %
When referring to macromolecular structures, what is meant by ‘covalent bonding’ and what are the physical properties of a covalently bonded solid? [6 marks]
6 marks - 12 points
> Covalent bonding happens between materials with half-filled outer shells.
> E.g. carbon or silicon.
> Electrons are shared between neighboring atoms.
> When electrons are shared, this produces atoms with full outer shells.
> Electrons bind the positive nuclei together
> through coulombs attraction.
> This leads to fixed bond angles
> due to repulsion of electron pairs.
> E.g. diamond and silicone – 109.5° .
> This will produce a very high melting temperature
> because those bonds are very strong.
> It is also an electrical insulator
> because there are no free electrons.
> Diamond is very brittle (non-ductile/non-malleable)
> because there are strong directional bonds.
> It is non-soluble
> because of the strength of the bonds.
