Covalent Compounds Learning Objectives 3.1 Describe a covalent bond as a pair of electrons shared between two atoms 3.2 Recall that covalent bonding results in the formation of molecules

Atoms Atoms are the basis of chemistry, and the basis of everything in the universe! Atoms make up matter, which makes up everything from a cup, to bones, to you! All atoms have the same basic structure. They have: electrons, which have a negative charge; protons, which have a positive charge and neutrons, which are neutral.

Draw the structure of an atom – label each part of your diagram

How are atoms of non-metals held together? Non metals combine together by sharing electrons. When two or more atoms join together, this is called a molecule.

How are atoms of non-metals held together? The atom hydrogen only has one electron and one proton. In the diagram below, hydrogen is held together by pairs of electrons. The way that these two atoms have joined up together is an example of covalent bonding. The first shell in all atoms can only have a maximum of two electrons, so here, both hydrogen atoms have a full outer shell of electrons

Metals & Non-Metals

Covalent Bonding Outer é are shared in PAIRS Full outer shell of 8 é (except H – which has 2 é) Between non-metal atoms Overlap the outer shell to show share of é Cl Cl Cl What would a double bond look like? A x between two atoms is a single Covalent Bond

Teacher notes This three-stage animation shows how covalent bonds form between atoms of different elements. While showing the animation, the difference between single, double and triple bonds could be pointed out.

Bonding Covalent Bonds – Dot & Cross Diagrams 1 Methane – CH4 5 2&3 4 6&7 C H C H C H C H + The C has 8 é in its outer shell Each H has 2 é in its outer shell Each bond has 2 é

Dot and cross diagrams Hydrogen Chlorine Hydrogen chloride Water

Bonding Covalent Bonds – Dot & Cross Diagrams Start with the molecular formula Identify the atom to put at the centre of the molecule – probably the one with the least number of atoms Draw the bonding arrangement by putting the other atoms around the central atom – leave hydrogen's to last Draw circles around each atom so the edges over lap – these are the bonds Draw electrons around the central atom (look at the Group number to find out how many electrons are in the outer shell) – put them one at a time at the points of a compass in a clockwise direction (unless you think there is a double bond) Do this for the other atoms At the end, each atom should “see” 8 electrons (except hydrogen which “sees” 2 and each “bond” should only have 2 electrons (unless it’s a double bond)

A few easy ones to start …. Hydrogen chloride – HCl Hydrogen – H2

A little trickier …. Ammonia – NH3 Water – H2O

The hardest ones you will get…. Chlorine – Cl2 Carbon dioxide – CO2

True or false? - Whiteboards

Dot and cross diagrams Dot and cross models show how a pair of electrons forms a covalent bond. Only the electrons in the outer shell of each atom are shown. The molecular formula for a compound can be worked out by counting how many atoms there. Copy and complete the table and draw the dot and cross diagrams

Covalent bonds Covalent bonds can form between two or more different non-metal atoms by sharing electrons.  They need to do this because they do not have the full outer shell of electrons that they would like. Atoms can share more than one pair of electrons if this is needed for each atom to have a full outermost shell. Two pairs of electrons form a double bond.

Which of these statements refers to covalent bonding? Only the electrons in the outermost shell are involved in bonding B These bonds can form between two different non-metal atoms C These bonds form between two different metal atoms D Atoms form bonds to get a full outer electron shell E two atoms of the same element F a metal and a non-metal atom G The atoms of one of the elements lose one or more electrons H Atoms share a pair of electrons I A compound’s formula depends on the numbers of outer shell electrons each atom has J gain one or more electrons

Summary Non-metal elements make covalent bonds by sharing electrons. The electrons used in these bonds are in the outermost shell. Atoms of the same or different type can share electrons to make covalent bonds. When two atoms join together, it is called a molecule. Atoms can share more than one pair of electrons if they need to fill the outermost shell. Two pairs of shared electrons form a double bond.

Summary questions What is a covalent bond? What is the type of diagram that is used to represent covalent bonds? How many covalent bonds are shown in the diagram below?

Answers A bond between non-metal ions formed by sharing electrons. Dot and cross 4 covalent bonds.

Formed between non-metal atoms (C)   Electrons are shared (C) CO2 is an example of this type of compound (C) http://www.rsc.org/periodic-table