Chapter 7 - Periodicity Flashcards
What is periodicity?
The term used to describe the repeating patterns seen within groups and periods on the periodic table
How did John Dalton arrange the elements in his periodic table?
In order of atomic weight, used pictorial symbols to represent both elements and compounds
How did John Newlands arrange his periodic table?
He arranged known elements in order of mass, grouping every 8 elements together in what he called the ‘Law of Octaves’.
What were the flaws in Newland’s table?
He left no gaps (assumed all elements had been found), elements in the same group were therefore not similar
How did Dmitri Mendeleev arrange his periodic table?
He put the elements in order of atomic mass, and then arranged them so periodic pattern in properties could be seen, left gaps for undiscovered elements using table to predict their properties
Which group was missing from Mendeleev’s periodic table and why did he omit it?
Group 8/0
It contains very unreactive (inert) noble gases, none of which had been discovered at the time
What is the trend across a period for electron configuration?
Each period starts with an electron in a new highest energy shell
For each period, the s and p sub-shells are filled in the same way
What is the trend down a group for electron configuration?
Elements in the same group have atoms with the same number of electrons in their outer shell, and the same number of electrons in each sub shell
What is ionisation energy?
Ionisation energy measures how easily an atom loses electrons to form positive ions
What is first ionisation energy?
The energy required to remove 1 electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
What is the general equation for first ionisation energy?
Element (g) → Element+(g) + e-
What is atomic radius?
The distance between the nucleus and the outer electrons
What is nuclear charge?
The number of protons there are in the nucleus of an atom
What is electron shielding?
The repulsion caused by inner shell electrons that reduces the attraction between the nucleus and outer shell electrons
What is the trend in first ionisation energy down a group (and why)?
First ionisation energy decreases down a group
This is because the atomic radius increases, and there are more inner shells so shielding also increases. Therefore the nuclear attraction on outer electrons decreases and so does the 1st IE
What is the trend in first ionisation energy across a period (and why)?
It increases across a period
Nuclear charge increases across a period, and there is similar shielding as elements have the same shell, nuclear attraction therefore increases and atomic radius decreases - 1st IE increases
Why does 1st IE fall in two places across period 2 and 3?
Paired electrons are easier to remove (repulsion) so it is easier to remove electron from O than N
2p subshell has higher energy than 2s subshell, so 1 electron in 2p is easier to remove, e.g. easier for B than Be
What is metallic bonding?
The strong electrostatic attraction between cations (positive ions) and delocalised electrons
What is the structure in metals?
Giant metallic lattice
What are the properties of metals?
- strong metallic bonds
- high electrical conductivity
- high melting and boiling points
Why can metals conduct electricity?
Due to the delocalised electrons which can move through the structure and carry charge
Why do metals have high melting and boiling points?
High temperatures are necessary to provide the large amount of energy to overcome the strong electrostatic attraction between cations and electrons
What is the solubility of metals?
Metals do not dissolve
What are giant covalent structures?
When many billions of atoms are held together by a network of strong covalent bonds to form a giant covalent lattice
What are the typical properties of substances with a giant covalent lattice structure?
- high melting and boiling point
- insoluble in almost all solvents
- non conductors of electricity (graphene and graphite are exceptions)
What is the structure of diamond?
A tetrahedral arrangement of carbon atoms (bond angles 109.5 by repulsion)
Why do giant covalent lattices have high melting and boiling points?
High temperatures necessary to break strong covalent bonds
Why are giant covalent lattices insoluble in almost all solvents?
Covalent bonds holding atoms in lattice are far too strong to be broken by interaction with solvents
What is the electrical conductivity of diamond, graphite and graphene (and why)?
Diamond - does not conduct as all 4 outer shell electrons are involved in covalent bonding
Graphene and Graphite - conducts as only 3 of outer shell electrons are used in covalent bonding, the remaining is delocalised (can carry charge)
What is the structure of graphene?
It is a single layer of graphite, composed of hexagonally arranged carbon atoms linked by strong covalent bonds - thinnest and strongest material ever made
What is the structure of graphite?
Composed of parallel layers of hexagonally arranged carbon atoms, layers bonded by weak London forces. Bonding in layers only uses 3 of carbon’s 4 outer shell electrons, so the spare electron is delocalised between layers
What is the periodic trend in melting point for Periods 2 and 3?
Melting point increases across from Group 1 to Group 4 (giant structures), then there is a sharp decrease in melting point between Group 4 and 5 as they are simple molecules. Giant structures require more energy to overcome their strong forces, whereas simple molecular structures only have weak forces to overcome
