Access to Science Learning aims: To recall the inter and intramolecular bonding present in atoms, ions or molecules. To look at assignment 2 To begin looking at trends in the periodic table News!

Elements and compounds Intramolecular bonds (bonds inside a substance) Metallic – groups 1 – 3 exist as an array of positively charged ions, with a sea of delocalised electrons Ionic bonding – metal and non-metal exist as an array of positive and negative ions with strong ionic bonding Covalent bonding – non-metal and non-metal exist as discrete or giant molecular structures joined by shared pairs of electrons (covalent bonds) Intermolecular bonds (bonds between molecules) London Dispersion forces – exist between all molecules (keep molecule in liquid or solid state) Weak polarised molecules have brief attraction for each other Dipole-dipole – a permanent force of attraction between partially positive and partially negative atoms on different molecules – occurs between polar covalent molecules. Hydrogen bonding – a stronger dipole-dipole force of attraction between partially positive hydrogen atoms and a nearby highly electronegative atom on another molecule,. N, O, F Occurs in proteins

Assignment 2

New topic – Periodicity https://www.bing.com/videos/search?q=history+of+the+periodic+table&FORM=HDRSC3#view=detail&mid=721D210CD2B6198120A3721D210CD2B6198120A3

Metals and non-metals (1) (18) (2) (13) (14) (15) (16) (17) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)

s-block elements p-block elements d-block elements f-block elements

Put the tail on the donkey!

Heisenberg’s uncertainty principle! Heisenberg suggested rather than we could say exactly where an electron could be found, he said that we could build a map to show the probability of finding an electron in a certain regions of space… 1s and 2s – electron density maps

A set of p orbitals visit website px orbital py orbital pz orbital x axis y axis z axis px orbital py orbital pz orbital visit website

A combined set of p orbitals y x z

Sub-levels s 2 2 s,p 2 6 8 s,p,d 2 6 10 18 s,p,d,f 2 6 10 14 32 Energy level Orbitals present Total number of electrons Maximum number s p d f 1 2 3 4 s 2 2 s,p 2 6 8 s,p,d 2 6 10 18 s,p,d,f 2 6 10 14 32

Atomic radius covalent radius atomic radius

Across a Period The atomic radius decreases. Outer electrons enter the same energy level (or one of a similar energy) but the number of protons in the nucleus increases. Thus the nuclear attractive force increases and the electrons are pulled closer to the nucleus decreasing the atomic radius.

Down a Group The atomic radius increases. Although the nucleus becomes more negative, the nuclear force on the valence electrons becomes weaker.

Down a Group (a) The outer electrons are further away from the nucleus. (b) Because of the increasing number of inner energy levels the outer electrons are shielded from the nuclear attraction. Thus, the nuclear force felt by the outer electrons is weaker and the atom is larger. This is called the shielding effect.

Formation of positive ions Ions of Groups I, II and III are formed by removal of all outer electrons. The number of protons in the nucleus remains the same but there are now fewer electrons to act on. The nuclear force on the remaining electrons is greater. In addition, the outer energy level has been lost. Thus positive ions are smaller than their corresponding atoms.

Formation of negative ions The number of protons in the nucleus remains the same but there are now more electrons to act on and so the nuclear force on each electron is weaker. Thus negative ions a larger than their corresponding atoms.

Melting points/oC H He -259 -270 Li Be B C N O F Ne 180 1280 2300 3730 -210 -218 -220 -249 Na Mg Al Si P S Cl Ar 98 650 660 1410 44 113 -101 -189

Our periodic table Group 1 Group 7 Period 3

Down Group I As the atoms get bigger so the metallic bond becomes weaker and the melting points decrease.

Down Group VII As the molecules get bigger so the van der Waals intermolecular forces become stronger and the melting points increase.

Melting points/oC giant covalent Si metallic bonding Al Mg molecular covalent P4 S8 Na Ar Cl2

Melting points across period 3 The rise from sodium to aluminium reflects the increasing strength of the metallic bond. Silicon has a high melting point because it has a giant covalent structure. Phosphorus to chlorine have low values because they are small covalent molecules. Argon consists of individual atoms with very weak van der Waals forces between them.

Ionisation energy This is the energy required to remove an electron from a gaseous atom. It is measured in kilojoules per mole (kJ mol-1) 1st ionisation energy This is the energy required to remove the first electron. M(g)  M+(g) + e- 2nd ionisation energy This is the energy required to remove the second electron. M+(g)  M2+(g) + e-

Ionisation energies across a period There is a general increase across a period because the atom size decreases and the nuclear force increases.

Ionisation energies down a group Ionisation energy decreases down a group because the atomic size increases and the nuclear force decreases.

Quiz State where the following can be found, group 1, group 7 or period 3. bromine group 7 sodium group 1 astatine phosphous period 3 chlorine group 7 and period 3 carbon period 2

Quiz Across a period the atomic radius increases. True or false? False What is the trend in melting point down group 1? decrease

Quiz What is the trend in ionisation energy across a period? increase What is the trend in ionisation energy down a group? decrease

Periodic Table click to return