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Covalent Compounds

Covalent Compounds. Learning Objectives. 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:

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Covalent Compounds

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  1. Covalent Compounds Learning Objectives

  2. 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.

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

  4. 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.

  5. 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

  6. Metals & Non-Metals

  7. Cl Cl Cl Cl 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 What would a double bond look like? A x between two atoms is a single Covalent Bond

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

  9. Dot and cross diagrams

  10. 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)

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

  12. Ammonia – NH3 Water – H2O A little trickier ….

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

  14. True or false? - Whiteboards

  15. 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

  16. 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.

  17. Which of these statements refers to covalent bonding?

  18. 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.

  19. 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?

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

  21. 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

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