As Topic 4 Notes - Bonding & Periodicity

Notes for bonding and periodicity

HideShow resource information
Preview of As Topic 4 Notes - Bonding & Periodicity

First 300 words of the document:

Topic 4a ­ Bonding
Revision Notes
1) Introduction
Atoms form bonds to get a full outer shell of electrons
Elements in Group 0 (He, Ne, Ar, Kr, Xe, Rn) do not normally undergo chemical
reactions as they have full outer shells and, so, do not need to form bonds to other
There are three types of bonding: ionic, covalent and metallic
Crystals (solids) have one of four types of structure: giant ionic, simple molecular,
giant covalent and giant metallic. Giant structures have millions of atoms or ions held
together in 3 dimensions. Simple molecular substances consist of a countable
number of atoms e.g. H2O, C12H22O11
Giant covalent is sometimes called giant molecular or macromolecular
To melt a substance the forces holding the particles together need to be broken
To conduct electricity there must something charged that can move (ions or
2) Types of Bonding
Ionic bonding ­ metals transfer electrons to nonmetals producing positive metal
ions and negative nonmetal ions. An ionic bond is an electrostatic attraction
between oppositely charged ions. Dotcross diagrams show outer electrons only
e.g. NaCl
Covalent bonding ­ A covalent bond is a shared pair of electrons. Only nonmetals
can get a full shell by sharing electrons. The bond is the attraction of the shared
electrons for the two nuclei. Dotcross diagrams show outer electrons only e.g. Cl2
In dative covalent bonds, one atom donates a lone pair of electrons to form the
bond. The atom accepting the electrons has an empty orbital
Examples of species that donate lone pairs include NH3, H2O, Cl
Examples of species that accept lone pairs include H+ and BF3

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Metallic bonding ­ metals lose their outer shell electrons to produce a lattice of
positive metal ions surrounded by delocalised (free) electrons.
3) Types of Structure
a) Giant ionic lattices e.g. sodium chloride
o Lattice of oppositely charged ions.
o High melting and boiling points (strong forces of attraction between ions
need to be broken).
o Do not conduct when solid (ions not free to move).
o Conduct when molten or dissolved in water (ions then free to move).…read more

Page 3

Preview of page 3

Here's a taster:

Structure of ice ( is hydrogen, is oxygen)
c) Giant metallic lattices e.g. magnesium
o Lattice of metal ions surrounded by delocalised electrons
o High melting and boiling points usually (strong forces of attraction between
metal ions and free electrons need to be broken)
o Conduct when solid as delocalised electrons can move
o Are malleable (bendy) and ductile (can be drawn into wires) because the
delocalised electrons allow the layers of ions to slide over each other
without repelling
d) Giant covalent lattices e.g.…read more

Page 4

Preview of page 4

Here's a taster:

Electronegativity and bond polarity
Electronegativity is the ability of an atom to attract the electrons in a covalent bond.
When there is a big difference in electronegativity between the atoms at either end of
a covalent bond the electrons will be pulled towards the more electronegative atom
(shared unequally).…read more

Page 5

Preview of page 5

Here's a taster:

Water, ammonia and HF have higher melting and boiling points than expected due to
the strength of the hydrogen bonds that have to be broken
o Ice is less dense than water because, in ice, the molecules are held further apart so
there is more space in the structure…read more

Page 6

Preview of page 6

Here's a taster:

Shapes of Molecules
The following procedure allows the shape of a molecule to be worked out:
Draw a dotcross diagram
Count number of electron pairs round the central atom
Pairs of electrons repel each other and get as far apart as
Lone pairs repel more than bonding pairs so bonds are pushed closer together
e.g. 107 in ammonia compared with the tetrahedral bond angle of 109.…read more

Page 7

Preview of page 7

Here's a taster:

Topic 4b ­ Periodicity
Revision Notes
1) Blocks in the Periodic Table
An element can be assigned to the s, p or d block by working out which sublevel its
outermost electron is in:
Na is 1s2 2s2 2p6 3s1 so is in the sblock
O is 1s2 2s2 2p4 so is in the pblock
Sc is 1s2 2s2 2p6 3s2 3p6 4s2 3d1 so is in the dblock
2) Ionisation Energies
a) First ionisation energy
Evidence that electrons are arranged in shells or energy…read more

Page 8

Preview of page 8

Here's a taster:

Trends Across Period 3 (NaAr)
Be able to describe and explain trends in the following:
1st ionisation energy Describe ­ general increase
Explain ­ bigger nuclear charge, same shielding
Dip from Mg to Al because Mg is losing 3s electron, Al is losing 3p.
3p is higher in energy, easier to remove.
Dip from P to S because P is 3p3, S is 3p4. Mutual repulsion of paired
electrons in S make electron easier to remove than in P.…read more


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »