Be prepared to answer the questions what are: relative atomic mass relative molecular mass relative...

Be prepared to answer the questions what are:

relative atomic massrelative molecular massrelative formula mass

Chemical bonding

Chemical Bonding

There are approximatley three types of bonding:

1. Ionic

2. Covalent

3. Metallic

Ionic bonding

This occurs between metals and non metals. Electrons are transferred from the metal to the non metal creating cations (+) and anions (-). These are then held together by electrostatic bonds because of their opposite charges.

Ionic compounds have high melting points, usually dissolve in water and conduct electricity when dissolved in water or molten

Ions and ionic bonding• Atoms of most elements have incomplete

outer shells.• They can lose or gain electrons in chemical

reactions to gain a full outer shell.• If this happens the atom is then charged and is

known as an ion.+

Ions and ionic bonding• Atoms of most elements have incomplete

outer shells.• They can lose or gain electrons in chemical

reactions to gain a full outer shell.• If this happens the atom is then charged and is

known as an ion.+Sodium atom

Na

Sodium ion Na+

Loss of electron

Ions and ionic bonding• A chlorine atom can gain an electron to

become a chloride ion.

-

Ions and ionic bonding• A chlorine atom can gain an electron to

become a chloride ion.

-Chlorine atomCl

Chloride ion Cl-

Gain of electron

Ionic bonding

Another example: Magnesium Fluoride.

Covalent bonding

This is where electrons are shared between atoms. The nuclei are attracted to the electrons between them.

One (bonding) pair of electrons gives a single bond.

The non bonding pairs of electrons are called lone pairs.

2 pairs of electrons forming a bond gives a double bond.

Covalent bonding• This is where atoms share electrons. They do

this to get a full outer electron shell.• A full outer shell gives them the same

electronic structure as a noble gas, which makes them very stable.

Example 1: two hydrogen atoms reacting to form one hydrogen molecule H2)

H H

Example 2: Hydrogen and chlorine form a covalent bond to give hydrogen chloride.

ClH

Covalent bonding

A dative covalent bond occurs when both electrons in the bond come from the same atom.

For examle in aluminium chloride:

Covalent bonding

Covalent molecules come in two main types which have different properties.

Network structures have high melting points whilst simple molecular structures have low melting points. Both tend to be insoluble in water and not conductors of electricity (except carbon).

Polarity and electronegativity

If two bonded atoms are different then they will attract the shared electrons to different extents.

The electrons feel greater attraction to the nucleus of smaller atoms and to atoms with a greater core charge.

The difference in attraction leads to polar bonds

Polarity and electronegativity

+ -- +

Polarity and electronegativity

Electronegativity is a measure of how good an atom is at attracting electrons to itself in a chemical bond.

There are several methods for estimating electronegativity they give different values but place elements in roughly the same order. The Pauling scale is commonly used

Polarity and electronegativity

We use the greek letter (delta) to describe bond polarity.

For example in HF:

And a carbon – fluorine bond:

Metallic

Metals can’t achieve stable electronic configurations by sharing electrons.

Instead they lose their electrons to form a lattice of regularly spaced positive ions in a ‘pool’ of delocalised electrons. Attraction between these electrons and the positive cores is metallic bonding

Metallic

Metals usually have high melting points, conduct electricity and are insoluble in water.

Chemical bonding

Covalent

Ionic

Bond polarity and

electronegativity

Shared electrons

DativeBonding pairs

Single bonds

Double bonds

Triple bonds

Lone pairs

Electron transfer

Anions (-)

Cations (+)

Electrostatic interactions

Chemical idea p43 Qs 1e,h, 2f,g, 4,5 7c,d,f

Intermolecular bonds

These are the bonds between molecules and there are three kinds:

1. Permanent dipole-permanent dipole2. Permanent dipole-induced dipole3. Instantaneous dipole induced dipole

What will better intermolecular bonding lead to in terms of physical characteristics?

Intermolecular bonds

Boiling points of the noble gases and single chain alkanes increase with size.

First of all though we need to know what a dipole is.

So we’ve met them before, some of the polar molecules from earlier are dipoles.

Intermolecular bonds

But not just polar molecules can have a dipole. Non-polar molecules can have instantaneous dipoles or can have dipoles induced in them,

So why do larger molecules have higher mpts? Because there is more contact there are more opportunities for induced dipoles to form

Section 5.3

Group 7

F

The Halogens – Group 7

Cl

Br

I

Fluorine is top of group seven and at room temperature it is a gas.

Chlorine is also a gas at room temperature.

Bromine is a dark brown liquid that gives off brown vapour at room temperatureIodine is a purple-grey solid at room temperature (if heated gently it forms a purple vapour)

•Going down the group the atoms get bigger.•Which means that the molecules get bigger.•Which means that the intermolecular forces between molecules increases.•Which means that the melting and boiling points get higher.

Group 7

Something a bit new.

Expansion of the octet. For example the chlorate (V) ion

ClO

OO

xxx x

xxx x

xxxxxx

xxx

xo

Group 7

Chemical properties:• Reaction with metals• Reaction with non-metals• Reaction with halides (displacement

reactions)• Oxidation of halides to give halogens• Reactions of halides with silver (I) ions

(precipitation)