3.1 The Periodic Table Flashcards
How is the periodic table arranged?
In order of increasing atomic number
Periods - horizontal row - increase from left to right - trends in chemical and physical properties (periodicity)
Groups - vertical column - elements with same chemical and physical properties due to same number of electrons in outer shell and same orbitals (same electron configuration)
What is the periodic trend in electron configurations?
Moving across a period, you can see that the number of occupied energy levels is the same as the period number
What is meant by the ‘classification of elements into s-, p- and d- blocks’?
The periodic table is structured into blocks that are linked to its sub-shells
The pattern mirrors the sub-shells that are being filled
What is first ionisation energy?
The energy required to remove one electron from each atom in one mole of gaseous element to form one mole of gaseous 1+ atoms
X (g) –> X+ (g) + e-
What is the trend in first ionisation energies in periods 2 and 3?
Moving across a period…
the number of protons increase so the nuclear charge is greater
shielding remains the same
attraction between the nuclei and electrons increase
more energy required to remove an electron - 1st ionisation energy increases
What is the trend in first ionisation energies down a group?
Moving down a group…
nuclear charge increases
shielding increases therefore distance between nuclei and outermost electron increases
attraction between nuclei and outermost electron decreases
less energy required to remove one electron - 1st ionisation energy decreases
Why are there small decreases in the first ionisation energy between group 2 and 13 elements?
Group 13 elements have outermost electrons in a p- orbital
Group 2 have theirs in an s- orbital
P- orbitals have slightly higher energy than s- orbitals - further away from nucleus
…electrons in p-orbitals are easier to remove
Why is there a decrease in first ionisation energy between group 15 and 16?
Group 15 contains only one electron in its p-orbital
In group 16 the outermost electron is spin-paired in the p-orbital - experience repulsion making it easier to remove an electron
What are successive ionisation energies?
A measure of how much energy is required to remove each electron in turn
Why is each successive ionisation energy higher than the one before?
As each electron is removed…
there is less repulsion between the remaining electrons
each shell is drawn closer to the nucleus
higher nuclear attraction - more energy required to remove each successive electron
What is metallic bonding?
The strong electrostatic attraction between cations and delocalised electrons
What is a giant metallic lattice structure?
The delocalised electrons are spread throughout the structure and can move
Over the whole structure the charges balance
A lattice of positive ions fixed in position with a sea of delocalised electrons that are mobile
What are the properties of giant metallic lattices?
High melting/boiling points - strong attractions between cations and delocalised electrons
Good electrical conductivity - delocalised electrons are mobile in a solid state
Malleable (hammered into different shapes) - mobile electrons means layers can slide past each other
Ductile (drawn out or stretched) - mobile electrons means layers can slide past each other
What are giant covalent lattices and the different types?
Strong covalent bonds making up a giant structure
Diamond - each Carbon atom forms four other Carbons around it - very hard
Graphene - 2D giant lattice, one carbon atom thick, of interlocking hexagonal Carbon rings - strong, light, conductor
Graphite - layered structure with delocalised electrons between layers - conductor
Silicon - networks of atoms bonded by strong covalent bonds
Why is there a variation in melting points across periods 2 and 3 (in terms of structure and bonding)?
As you move across periods 2 and 3 the elements change from metals to non-metals and from solids to gases
What are the trends in melting points in the groups?
Group 1 - 14
…melting points increase steadily as all are giant structures
Group 14 - 15
…sharp decrease in melting point because elements have simple molecular structures (weak intermolecular forces)
Group 15 - 18
…low melting point as it has simple molecular structure
Why does reactivity increase down group 2 elements?
To achieve the electron configuration of a noble gas, 2 electrons must be lost
Two outer electrons are easier to lose down the group
Therefore reactivity increases due to the fact that…
each successive element has its outer electrons at higher energy levels;
a larger atomic radius and increased shielding
