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Recap – Ions and Ionic Bonding

Recap – Ions and Ionic Bonding. Cations are positively charged and formed from metals. Anions are negatively charged and formed from non-metals . Cations and anions are formed at the same time by electron transfer .

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Recap – Ions and Ionic Bonding

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  1. Recap – Ions and Ionic Bonding • Cations are positively charged and formed from metals. • Anions are negatively charged and formed from non-metals. • Cations and anions are formed at the same time by electron transfer. • Anionic bond is the electrostatic attraction between cations and anions.

  2. Ionic Bonding Cl Na + • It takes energy to remove an electron from an atom. • Electrostatic attraction between cations and anions supplies energy. • Generally do not get very highly charges ions as too much energy is required to form them. - + Na Cl 6 230 kJ 1 090 kJ 2 360 kJ 4 630 kJ C C+ C2+ C3+ C4+ e- e- e- e-

  3. F Sharing of Electrons In ionic compounds a Noble gas electron configuration is obtained by transfer of electrons. In covalent compounds a Noble gas electron configuration is obtained by sharing of electrons. F F F

  4. Sharing of Electrons H2

  5. Reason for Covalent Bonding • Electrons are shared to achieve a Noble gas configuration for each atom. • Electron density between the two atoms: the bond is directional. • Only electrons from the outermost shell can be involved in bonding – valence electrons. • Electrons tend to form pairs.

  6. Covalent Bonding: C and H • Carbon has 4 electrons in outer shell – needs 8 • Hydrogen has 1 electron in outer shell – needs 2 H C H H H

  7. Covalent Bonding - methane CH4 H C H H H

  8. Covalent Bonding - water • Oxygen has 6 electrons in outer shell – needs 8 • Hydrogen has 1 electron in outer shell – needs 2 O H H

  9. Covalent Bonding – H2O • We can identify bond pairs and lone pairs (or non-bonding pairs) of electrons O H H

  10. Covalent Bonding: N and H • Show only valence electrons

  11. Valence • Valence electrons are used in bonding. • The valence of an atom is the size of the charge if it forms an ion or the number of bonds it forms in a neutral molecule. 1 2 3 4 3 2 1

  12. Diatomic Molecules • The diatomic elements (eg H2, N2, O2, F2) all have a similar formula but different bonding requirements. H2 Single Bond F2 Single Bond

  13. Bonding Requirements • Double bonds occur where two electron pairs are shared between atoms. O2 Double Bond

  14. Bonding Requirements • Triple bonds occur where three electron pairs are shared between atoms. N2 Triple Bond

  15. Learning Outcomes: By the end of this lecture, you should: understand the difference between ionic and covalent bonding be able to draw diagrams representing the bonding in simple molecules know the difference between a bond pair and lone pair of electrons know the valence of elements in groups 1, 2, 13 – 17 be able to predict the formula of simple covalent compounds appreciate the difference between a single, double & triple bond be able to complete the worksheet (if you haven’t already done so…)

  16. Questions to complete for next lecture: • Would the following pairs of elements form ionic or covalent bonds? H and O, Na and O, N and O, S and O. • Draw a diagram representing the molecule HCN. • How many lone pairs does each of the following molecules possess? H2, Cl2, H2S, HBr. • Oxygen has a valence of 2. Give an example of an ionic compound and a covalent compound containing oxygen that illustrates this concept. • Predict the formula of the simplest compounds formed between sulfur and fluorine, phosphorus and chlorine, magnesium and iodine.

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