Ionic Bonding Describe the formation of positive and negative ions. Draw dot and cross diagrams for ions of group 1 and 7 elements. Draw dot and cross for other elements.

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

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

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)

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

Ionic bonding E.g. Sodium + Chlorine → Sodium chloride Cl Na Outer shells not full!

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

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

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 for ions of: Calcium and oxygen Beryllium and oxygen

Covalent Bonding Describe the formation of covelant bonds. Draw dot and cross diagrams. Describe the electron arrangement in covelant molecules with 3 or more different types of atoms. Describe the formation of double and triple bonds.

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.

Covalent bonds Covalent compounds are held together by this sharing of electrons. It is sometimes represented in full bonding diagrams (see figure 1). Often these bonds are just shown as a line (see figure 2). O H - Figure 1 Figure 2 - H

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

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)

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

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

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

Three or more atoms present CH3OH - Methanol

Draw a dot and cross diagram for: Chloromethane CH3Cl

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

Questions Describe the formation of covelant 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