Yr 10 Chemistry Covalent Bonding

 Questions of Doom Starter

 TO KNOW to term covalent bonding  TO BE ABLE to draw the atomic structures to show covalent bonding  TO UNDERSTAND the differences between ionic and covalent bonding Objectives

 Ionic Bonding is between a METAL and NON-METAL  This is easy because metals form CATIONS and non- metals form ANIONS.  But what happens for compounds and molecules in which both are NON-METALS???????? (e.g. O 2, H 2 O, NO 2 ) Remember…….

Covalent compounds  Covalent compounds are formed when non-metal atoms react together.  As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become SHARED by the atoms.  The shared electrons count towards the shells of both atoms and therefore help fill up incomplete electron shells.

Covalent bonds  Covalent compounds are held together by this sharing of electrons. covalent bond.  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 XXXX F F F - Figure 1Figure 2

Small covalent structures  Sometimes just a few atoms join together in this way.  This produces small covalent molecules – often known as simple molecular structures. a simple molecular structure covalent bonds

Giant covalent structures  Sometimes millions of atoms are joined together by covalent bonds. giant lattice.  This produces a rigid 3-D network called a giant lattice. a giant lattice covalent bonds

Covalent bonding and electron structures  The driving force for covalent bonding is again the attainment of outer electron shells that are completely full.  This is achieved by sharing electrons where the shared electrons count towards the outer shells of both atoms.  Sometimes this is achieved with equal numbers of each type of atom. Sometimes it is not! Cl C H HH H N H HH H

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 (2,8,8) Cl (2,8,8) Cl-Cl

Both fluorine and chlorine needs 1 more electron to attain a full electron shell. Cl (2,8,7) F ( 2,7 ) Copy this diagram and add the electron arrangements that could exist in fluorine chloride (FCl). Cl (2,8,8) F ( 2,8 )

Covalent bonding in hydrogen chloride Both hydrogen (1) and chlorine (2.8.7) needs 1 more electron to attain a full outer shell. H (2) Cl (2,8,8) H-Cl Cl (2,8,7) H (1)

Covalent bonding in water Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more. Therefore, we need 2 hydrogens. O H H O H H O H H

 Hydrogen (1) needs 1 more electron. How many does nitrogen (2.5) need? How many hydrogens per 1 nitrogen? Draw bonding diagrams for ammonia. N H H H N H H H 3 3

 Hydrogen (1) needs 1 more electron. How many does carbon (2.4) need? How many hydrogens per 1 carbon? Draw bonding diagrams for methane. 4 4 C H H H H C H H H H

H H O O H H O O  Copy the atoms below.  Complete the diagram showing how each atom can achieve full shells.

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 O O=O O O 4 electrons

Nitrogen (2.8.5) needs 3 more electrons to attain a full electron shell and forms a triple bond. Draw a bonding diagram of nitrogen. 6 electrons N N N N N=N

1.Hydrogen fluoride (HF) 2.Hydrogen sulphide (H 2 S) 3.Ethane (C 2 H 6 and the carbons are joined by a single covalent bond) 4.Carbon dioxide (CO 2 and the carbon oxygen bonds are double bonds) H F H H S H H H H H H CC CO O Draw ‘dot and cross’ type bonding diagrams for each of the following:

Giant covalent structures 1.Carbon atoms form giant structures. 2.What is interesting is that there is more than one possible arrangement for the atoms. 3.Although this does not affect the chemical properties it can make a huge difference to the physical properties such as hardness, slipperiness, melting point and density. Different arrangements of the same element are called allotropes. C

Giant covalent structures: diamond  One form of carbon is diamond.  Each diamond consists of millions of carbon atoms bonded into a single giant structure. very  It is very hard. Diamond strong covalent bonds carbon atoms

Giant covalent structures: graphite  A more common form of carbon is graphite.  Millions of carbon atoms are bonded into a giant structure but within this structure the layers are only weakly joined.

Giant covalent structures: carbon footballs!  During the last 20 years new forms of carbon have been discovered some of which have “closed cage” arrangements of the atoms.  These are large but are not really giant molecules. One of them contains 60 carbon atoms and bears remarkable similarities to a football!

Giant covalent structures: sand  Sand is an impure form of silicon dioxide.  Although it is a compound, it has a giant covalent structure with certain similarities to diamond.