The way things are joined together Bonding The way things are joined together

24 12 Mg electron - 12 proton + neutron

Atoms can be joined together in 3 possible ways Metal and non-metal Non-metals only Metals only Ionic Bonding Covalent Bonding Metallic Bonding All three types involve changes in the electrons in the outermost electron shells of the atoms

Ionic bonds + and - charges

Most ionic compounds contain a metal and a non-metal. When metals react they lose outer shell electrons to leave a full electron shell. This produces a charged atom (ion) with a + charge. Lose 1 or more electrons Neutral atom n+ Positive ion When non-metals react with a metal they gain electrons to achieve a full electron shell. Gain 1 or more electrons Neutral atom n- Negative ion

Has ? Electrons in outer shell 19 9 F Has ? Electrons in outer shell Does it need to pick up or lose electrons to make the outer shell full

Now has more negative electrons than positive protons Gains 1 electron Now has more negative electrons than positive protons = a negative charge 19 9 F

Now has more positive protons than negative electrons 24 12 Mg Loses 2 electrons Now has more positive protons than negative electrons = a positive charge

Cl Cl Na Na+ Loses 1 electron Sodium atom (2.8.1) Sodium 1+ ion (2.8.0) Cl Cl Gains 1 electron (from sodium) Chlorine atom (2.8.7) Chlorine I - ion (2.8.8)

The oppositely charged ions are attracted into a lattice that gets bigger and bigger until it consists of millions of ions + - + - opposites attract

We have shown ions attracting and building into a 2 dimensional sheet. + - In fact the whole process will be going on in three dimensions to build up a giant 3-D lattice. + - + -

Ionic compounds are very brittle. Opposite charges attract, so neighbouring ions are pulled together. When something hits the substance a layer of ions will be pushed so that they are next to ions with the same charge. Attraction becomes: + - + - repulsion! + - Blow - +

Ionic substances do not conduct electricity as solids. When molten or dissolved they will conduct (and also undergo electrolysis). This is because the electricity is carried through the solution by the ions which are free to move when the ionic compound is molten or in solution. + - Solid – not free to move Doesn’t conduct - + Molten – mobile Does conduct

The ionic bonds are very strong. Will that make ionic compounds have a high or low boiling point? High

Covalent bonding Sharing.

Covalent compounds are formed when non-metal atoms react together. The atoms share electrons

- F Covalent compounds are held together by this sharing of electrons. A pair of electrons shared in this way is known as a covalent bond. It is sometimes represented in full bonding diagrams (see figure 1). Often these bonds are just shown as a pair of electrons (xx) or even just a line (see figure 2). F X - Figure 1 Figure 2

There can be small covalent molecules and large covalent molecules

Chlorine (2.8.7) needs 1 more electron to attain a full electron shell. Cl (2,8,7) Cl (2,8,7) Cl-Cl Cl (2,8,8) Cl (2,8,8)

Hydrogen (1) needs 1 more electron but oxygen (2. 6) needs 2 more Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more. Therefore, we need 2 hydrogens. O H O H O H

The bonds between ATOMS that share electrons are STRONG The bonds between molecules that don’t share electrons are WEAK What effect will this have on the melting and boiling points? Will they be high or low? Low

Do these covalent molecules conduct electricity? Will they dissolve in water and spread out like ionic solids? No No

Metallic bond

The protons sit in a sea of electrons Metallic bonding is the attraction of + metal ions for the “sea of electrons.”

The metal atoms are the same and exist in simple structures. Metals are not brittle. The metal atoms are the same and exist in simple structures. If something hits the substance, it simply moves to the next layer along. Blow

If the sea of electrons can flow, will metals conduct electricity? Like ionic bonds the metallic bonds are strong. Will melting points be high or low? High If the sea of electrons can flow, will metals conduct electricity? yes

Name of chemical Sucrose Sodium chloride Ethanol Copper sulphate Melting point – high or low   Does it conduct electricity as a solid? Does it conduct electricity in aqueous solution