module 3 - periodic table and energy Flashcards
periodicity definition
repeating pattern of physical and chemical properties
how is the periodic table arranged
- by increasing atomic number of elements
how are periods and groups organised
periods = similar chemical and physical properties
groups = similar chemical properties
where are the s,d,p and f blocks located
s = left
p = right
d = middle
f = bottom
electron shielding definition
electron shielding is the decrease in the attraction of the outer shell electrons in the nucleus.
the greater the number of shells, the greater the electron shielding
how does electrons shielding affect ionisation energy
when electron shielding increases, ionisation energy decreases as it requires less energy to remove the outer shell electron
how does electron shielding differ across a period
electron shielding remains the same across a period because each period has the same number or shells
how does electron shielding differ down a group
electron shielding increases down the group because there are more shells as you go down the group
why are there small decreases in first ionisation energy in periods 2 and 3
-magnesium - the outer electrons are in a 3s orbital, whereas in aluminium the outer electron is in a 3p orbital. The 3p orbital is further from the nucleus so there is more electron shielding and distance from the nucleus so electrostatic attraction decreases. The second drop is from Phosphorus to Sulphur. This is because it is the first time electrons are paired up in 3p orbitals, so there is added electron-electron repulsion.
first ionisation energy definition
the energy required to remove one electron from each atom in one mole of gaseous atoms
how does atomic radius differ across a period
atomic radius decreases because:
- nuclear charge increases
- electron shielding remains the same
how does atomic radius differ down a group
atomic radius increases because:
- increased number of shells
- increased shielding
trend in first ionisation energy across periods 2 and 3
- first ionisation energies will increase
- as you go along a period, atomic number increases (number of protons in nucleus) which means that atomic radius decreases and so there is a stronger electrostatic attraction between electrons and the nucleus
- however there are small decreases in the first ionisation energy
why are there small decreases in first ionisation energy across periods 2 and 3
- highest energy electron occupying a p orbital, which is slightly higher in energy than an s orbital.
- so there is a dip in first ionisation energy
metallic bonding definition
strong electrostatic attraction between cations (positive ions)
and delocalised electrons
what structure do metals form
giant metallic lattice structures
components of giant metallic lattice structures
- each metal atom forms a positive ion
- the positive ions are arranged into a regular lattice structure
- outer shell electrons are delocalised which can move through the structure, and conduct electricity
in which part of the periodic tables are giant covalent lattices formed
right side
mtp and btp of giant covalent lattices
- very high
- large amount of energy needed to break strong covalent bonds between atoms
what lattices does carbon form
diamond, graphite and graphene
structure of diamond and silicon
- form giant 3D structures with atoms bonded in a tetrahedral arrangement by covalent bonds
- all 4 outer shell electrons involved in covalent bonding so the electrons cannot move and are unable to conduct electricity
structure of graphite
- forms a giant planar structure with many planes weakly held together by covalent bonds
- 3 outer shell electrons involved in covalent bonding within each layer, which means the outer shell can move and conduct electricity
graphene structure
single layer of atoms held together by covalent bonds
trend in melting points for giant metallic lattices
- giant metallic lattice held together by strong metallic bonds between positive ions and delocalised electrons
- large amount of energy needed to break the metallic bonds and melting points are high
- melting point increases from lithium-beryllium and from sodium-magnesium-aluminium because the charge on the positive ion and number of delocalised electrons both increase.
- attraction between particles increase and more energy is needed to break the metallic bonds
trend in melting points for giant covalent lattices
- lattice held together by strong covalent bonds between atoms
- large amount of energy is needed to break the covalent bonds and the melting points are high
trend in melting points for simple molecular lattices
- weak london forces between molecules hold the lattice together
- small amount of energy is needed to break the london forces and the melting points are low
- fluctuations in melting points of multiple elements because london forces increase with the number of electrons in the molecules so it requires more energy to break those bonds
solubility of giant covalent and metallic structures
- A substance can dissolve. in water if it forms strong enough attractions with water molecules. Giant covalent and metallic substances cannot form these strong attractions with water, so they are insoluble.
why is there decreases in mpts and bpts across periods 2 and 3
- as we go across these periods, we are met with the metals first. for metals they have a large number of delocalised electrons which increases the strength of the metallic bonds that hold the metal together. because the metallic bonds are so strong, the melting point increases as it requires more energy to break these bonds.
- once we reach the non metals in periods 2 and 3, the mpt decreases significantly
- non metals arent held together by metallic bonds and in the case of oxygen and fluorine, their molecules are held together by weak dispersion forces. and in neon, the atoms are held together by weak dispersion forces. because these forces are so weak, it requires little energy to break the bonds
successive ionisation energy definition
- the energy that is required to remove the electron one after the other.
what does successive ionisation energy depend on
- the number of electrons present in the outermost shell.
why does successive ionisation energy increase between shells
- because the closer the shell is to the nucleus, the easier it is to remove an electron from that shell
- for example, in sodium, it has one outer shell electron and there is a big jump in ionisation energy from the first to second. This is because the second electron is being removed from a shell that is much closer to the nucleus, meaning there is stronger attraction from the nucleus.
atomic radius trend as you go down a group
increases as you go down a group in the periodic table because extra electron shell is added each time, so the distance between the nucleus and outermost electron increases. This means that the attraction between the outermost electron and nucleus decreases
atomic radius trend as you go across a period
- decreases slightly as you go across a period, as the nuclear charge of the nucleus increases, which means that the nucleus pulls the outer electrons closer to it, which decreases the atomic radius.
trend in successive ionisation energy as you go down a group
Ionisation energy decreases down a group because atomic radius increases and the outer electrons are shielded from the nucleus by inner electron shells.
trend in successive ionisation energy as you go across a period
Ionisation energy generally increases across a period because nuclear charge increases.
what do group 7 elements exist as
diatomic molecules
mpts and bpts of group 7
strong covalent bonds between atoms, weak intermolecular forces, so low mpts and bpts
trend in mpts and bpts as you go down group 7
bpts and mpts increase as you go down the group - larger atoms = more electrons = stronger london forces = more energy needed to break these bonds
reactivity trend as you go down group 7
reactivity decreases as you go down
more shells = more shielding effect = less nuclear attraction
benefits and risks of chlorine water
- can kill bacteria in water
- chlorine is toxic and respiratory irritant
- reacts with organic compounds to make haloalkanes - can be carcinogenic
redox reactions in group 7
- most common reaction in group 7
- each halogen becomes reduced (gains an electron)
- behaves as an oxidising agent - removes electron from other substances
disproportionation definition
the reaction in which the same element becomes simultaneously oxidised and reduced
examples of disproportination reactions
chlorine + water
Cl2 + H2O –> HCl + HClO
chlorine with sodium hydroxide
Cl2 + 2NaOH —> NaClO + NaCl + H2O
test for halide ions
method:
- take 5cm^3 of unknown solution
- add 3-5 drops of nitric acid followed by 3-5 drops of silver nitrate solution
positive result:
- chloride = white precipitate
- bromide = cream precipitate
- iodide = yellow precipitate