1. Bonding

2. Compound Element Atom Molecule
A particle containing 2 or more atoms (of the same or different types
Compound
The simplest type of particle
Element
A substance made of 2 or more types of atom chemically combined
Atom
A substance made of only 1 type of atom
Molecule

3. Atoms bond by
Sharing electrons – covalent bonds (between non-metals only)
Gaining or losing electrons – ionic bonds (between metal and non-metal)
Unfixed sharing electrons – metallic bonds (between metals only)
All three types involve changes in the electrons in the outermost electron shells of the atoms

4. Electron shells and bonding
Atoms are only “happy” when their outer shell is full
They will either lose or gain electrons in order to become “happy”
If they lose electrons they become positive ions (the number of protons is bigger than the number of electrons)
If they gain electrons they become negative ions (the number of protons is smaller than the number of electrons)

5. General rule Non-metals usually form negative ions
Metals usually form positive ions

6. Ionic bonding E.g. Sodium + Chlorine → Sodium chlorideCl Na
Outer shells not full!

7. Ionic bonding E.g. Sodium + Chlorine → Sodium chloride
NaCl (Na+Cl-) Cl Na
Copy example
Both ions have full outer shells

8. Beryllium fluoride - BeF2
Each beryllium atom need to loose two electrons, but each fluorine only needs 1 2+ F
Copy example Be F

9. Questions Describe the formation of positive and negative ions
Draw ‘dot and cross’ diagrams for ions of:
Potassium and bromine
Lithium and chlorine
3. Draw ‘dot and cross’ diagrams for ions of:
Calcium and oxygen
Beryllium and oxygen

10. Covalent compounds
Covalent compounds are formed when NON-METAL atoms react together.
Covalent bonding – bonding in which a pair of electrons, one from each atom, is shared between two atoms.

11. Covalent bonds
Covalent compounds are held together by this sharing of electrons.
It is sometimes represented in full bonding diagrams Often these bonds are just shown as a line. O H - - H

12. Covalent and electron structures bonding
The purpose of covalent bonding is to gain a full outer electron shell.
This is achieved by sharing electrons where the shared electrons count towards the outer shells of both atoms. O H Cl C H
Water C O
Chlorine
Carbon dioxide N H
Methane
Ammonia

13. Covalent bonding in chlorine
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)

14. Hydrogen (1) needs 1 more electron.
How many does carbon (2,4) need? 4
How many hydrogens per 1 carbon? 4 C H C H

15. Covalent bonding - multiple bonds
Mostly electrons are shared as pairs.
There are some compounds where they are shared in fours or even sixes.
This gives rise to single, double and triple covalent bonds.
Again, each pair of electrons is often represented by a single line when doing simple diagrams of molecules.
Cl-Cl
Single bond
O=O
Double bond
N=N
Triple bond

16. Covalent bonding in oxygen
Oxygen (2,8,6) needs 2 more electrons to attain a full electron shell. O X O
O=O
4 electrons O X

17. Three or more atoms present
CH3OH - Methanol

18. Draw a dot and cross diagram for:
Chloromethane CH3Cl

19. Bonding and physical properties
Covalent compounds are insoluble in water unlike ionic
Covalent compounds don’t conduct electricity in water
There are no ions in covalent compounds, unlike ionic compounds.
Covalent compounds generally have much lower melting and boiling points than ionic.
Interact with each other through ‘weak’ INTERMOLECULAR FORCES H O
electrons fixed in covalent bonds

20. Questions Describe the formation of covalent bonds
Draw dot and cross diagrams for hydrogen, water, and hydrogen chloride
Describe the electron arrangement in covelant molecules with 3 or more different types of atoms
Describe the formation of double and triple bonds