Chemistry As, Unit 3

Why do Ionic compounds have high melting/boiling points

Strong electrostatic forces of attraction between particles

What does Brittle do (ions)

Forces ions to move, causing ++ and - - charge to come together. They then repel one another and the compound breaks.

What does Isoelelectronic mean?

ions/ atoms or molecules having the same electronic structure and having the same number of electrons

Ionic or covalent?

Ionic

Ionic or covalent?

Covalent

Ionic or covalent?

Covalent

Ionic or covalent?

Ionic

What is polarisation

When a positive ion pulls the electrons from the negative ion towards it

Define Electron negativity

The ability for an atom to pull electrons towards itself

What does polar mean?

The separation of a charge with a clear positive/negative end

What is a polar covalent bond

Bond where one bond has a slight positive charge and one slight negative charge

How do we know if bond is polar?

• central atom has a lone pair

• All atoms are the same

• Less EN atom gets a +S charge

• More En atom gets a -S charge

Electron negativity definition + when it decreases or increases (periodic table)

• The ability of an atom to attract a shared pair of electrons.

• Going from left to right EN increases

• Going down the group EN decreases

Define and explain Dative covalent bond

The complete shared pair of electrons given by a single atom (Donner)

Linear

Draw, degree, bond count, lone pair

Cl - Be - Cl

180’

Bond, 2

Lone, 0

Trigonal planer

Draw, degree, bond count, lone pair

120’

Bond, 3

Lone, 0

Tetrahedral

Draw, degree, bond count, lone pair

109.5’

Bonds, 4

Lone, 0

Trigonal Bipyramidal

120’ , 90’

Bond, 5

Lone, 0

Octahedral

Draw, degree, bond count, lone pair

90’

Bond, 6

Lone, 0

Trigonal pyramidal

Draw, degree, bond count, lone pair

107’

Bond, 3

Lone, 1

V- shaped

Draw, degree, bond count, lone pair

104.5’

Bond, 2

Lone, 2

Simple molecular structure

• eg H2, O2, Br2

• Week intermolecular forces between molecules

• Joined by covalent bond

• Low melting/ boiling points

Giant covalent structure

• Elements: Si, Diamond, graphite, graphene

• Lattice structure where all atoms joined together by covalent bonds

• High melting/ boiling point

Ionic structure

• compounds with metal and non-metal

• Lattice structure of positive and negative ions

• Ion held by strong forces of attraction with + and - ions

• High melting/ boiling points

Metallic structure

• Element: metals

• Lattice structure of metal atoms where outer shell electrons from each atom are delocalized.

• Strong attraction between positive nucleus of atoms in a sea of delocalised electrons.

• High melting/ boiling points

Finding non-polar molecules

• if molecule has same atoms eg O2, N2

• Made of only carbon and Hydrogen atoms

• Central atoms:

-Has no lone pair

-same bonded around the central atom

Malleable

Materials ability to deform or shape into thin sheets without breaking

Ductile

Ability to stretch material into thin or thread without breaking when pulling

Brittle

A material that fractures with little to no deformation under a pressure

Characteristics of a Sigma bond

• made of head-to-head overlap between orbitals

• Shared electron density lies along the central line

• Strong bond

Characteristics of a PI-bond

• made of a sideways overlap between orbitals

• Shared electron density lies above and below the central line

• Weak bond

What is the electron-pair repulsion theory?

Both repel each other therefore now move as far apart as possible to reduce repulsion.

Difference of bond length and angle

• One length is the distance between 2 bonded atoms

• Bond angle is the angle between 2 bonds that share common atoms