Module 3: Chapter 7 (Periodicity)

• by increasing atomic (proton) number • in periods showing repeating trends in physical and chemical properties (periodicity) -> number of period gives the highest energy electron shell • in groups having similar chemical properties -> same number of electrons in the outer shell

• Dimitri Mendeleev published his periodic table in 1865 with 60 elements • he arranged them in order of atomic mass and lined up elements in groups with similar properties • swapped elements around if they didn’t fit properties and left gaps for elements that weren’t discovered yet • today the period table has 118 elements arranged by increasing atomic number

A repeating pattern across periods is called periodicity

The energy to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

The greater the distance between the nucleus and the outer electron the weaker the attraction

the more protons in the nucleus the stronger the attraction

the shielding effect is the repulsion between the inner and outer shell electrons as electrons are negatively charged

shielding increases when the number of inner shells increases, reduces the attraction between the nucleus and outer electrons

As each electron is removed the remaining electrons are pulled closer to the nucleus - nuclear attraction increases

increases as you move across the group

This is because the atomic radius increases and shielding increases, therefore weaker attraction between outer electron and nucleus.

• Electrons are in the same shell so shielding is similar. • Nuclear charge increases (more protons in nucleus) • Nuclear attraction decreases (between nucleus and outer electrons) so atomic radius decreases • First ionisation energy increases as attraction between outer electrons and nucleus increases

In B, electron is removed from a 2p orbital rather than 2s orbital in Be. The 2p sub-shell is at higher energy and its electron is easier to remove

In O, one of the 2p orbitals contains paired electrons whereas in N, all three orbitals are singly occupied The paired electrons in O repel and electron is easier to remove

In a SOLID… • a regular repeating pattern of fixed cations (maintain shape) • delocalised electrons spread out in the whole structure (each atom donated one outer shell electron), act as mobile charge carriers

Electrostatic attraction between cations and delocalised electrons

• conduct electricity in a solid or liquid state as there as mobile charge carriers • high melting and boiling points because of the strong electrostatic attraction • insoluble in all solvents

• high melting and boiling points as there are very strong covalent bonds • insoluble in almost all solvents, as they’re held in a lattice and bonds are too strong to be broken down by interactions with solvents • non-conductors of electricity except for graphene and graphite as there are delocalised electrons between layers as carbon only bonds 3 times

• billions of atoms held together by strong covalent bonds, forms a giant covalent lattice

• strong covalent bonds between atoms within the molecules with only weak attractive forces between molecules • for elements the molecules will always be non-polar so the intermolecular forces are London Forces

• low melting and boiling points (not as much energy is required to overcome the weak intermolecular forces) • the more electrons in the molecule the stronger the London forces, and the higher the melting and boiling points

• Each carbon forms 4 single covalent bonds to another C atom (tetrahedral shape) • a non-conductor of electricity

• one layer of graphite • each carbon only uses 3 of its outer shell electrons to form a planar hexagonal layer • remaining electrons are delocalised in the layer, making them excellent conductor

layers of graphite stacked together, attracted by weak forces