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# 2 Atomic Structure

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### 2 Atomic Structure

1. 1. 2 Atomic Structure
2. 2. Properties of subatomic particles Outside nucleus 0 -1 Electron nucleus 1 0 Neutron nucleus 1 +1 Proton Location Relative mass(amu) Relative charge Name
3. 3. Terminology for the Atom <ul><li>Atomic no (Z): no of protons </li></ul><ul><li>Mass No (A): no of protons + no of neutrons </li></ul><ul><li>Isoptopes: atoms of the same number of protons (the same element) but different numbers of neutrons </li></ul><ul><li>Atomic mass unit: 1/12 the mass of a carbon-12 atom. The mass of a carbon-12 atom is defined as exactly 12 atomic mass units </li></ul><ul><li>Atomic mass: the average of the masses of an elements naturally occurring isotopes weighted to their abundances </li></ul>
4. 4. Isotope Calculations <ul><li>Boron has 2 isotopes 10 B and 11 B. They are present in naturally occurring boron respectively at 18.7% and 81.3%. Calculate the relative atomic mass of boron. </li></ul>Ar = (18.7 x 10) + (81.3 x 11) 100 = 10.8
5. 5. <ul><li>The element copper has relative atomic mass 63.55 and contains atoms with mass numbers 63 and 65. What is the percentage composition of a normal isotope of copper? </li></ul>65x + ((100-x) x 63) = 63.55 100 65x + 6300 – 63x = 6355 2x = 6355-6300 x = 27.5% 100 – x = 72.5% % composition = 27.5% 65Cu 72.5% 63Cu
6. 7. Bonding Terminology <ul><li>Ionic compounds: form when an atom of one element transfers electrons to an atom of another element </li></ul><ul><li>Covalent compounds: form when two atoms share electrons </li></ul><ul><li>Ion: a charged particle </li></ul><ul><li>Cation: a positively charged particle </li></ul><ul><li>Anion: a negatively charged particle </li></ul><ul><li>Monoatomic ion: an ion composed of a single aton </li></ul><ul><li>Polyatomic ion: two or more atoms bonded covalently and having net positive or negative charge e.g. NH 4 + , SO 4 2- </li></ul>
7. 8. Electronic Configuration <ul><li>Electrons are present in shells around the nucleus </li></ul><ul><li>The first shell can hold 2 electrons, the second 8 and the third 18 </li></ul><ul><li>The no of outer shell electrons is the same as the group no </li></ul>
8. 9. <ul><li>Find the electronic configuration of sodium </li></ul>Na atomic no = 11  there are 11 protons and 11 electrons Electronic Configuration is 2,8,1 Find the electronic configuration of chlorine Cl atomic no = 17  there are 17 protons and 17 electrons Electronic configuration is 2,8,7
9. 10. Compounds <ul><li>Ionic compounds are formed between a metal and a non metal e.g. magnesium chloride </li></ul><ul><li>Covalent compounds are formed between two or more non-metals e.g ammonia (NH 3 ) </li></ul>
10. 11. Formation of Covalent Bonds Drawing dot and cross diagrams <ul><li>Only outer shell electrons are shown </li></ul><ul><li>Dots and crosses used to distinguish electrons from different atoms </li></ul>
11. 12. x o o o o o o o x o o o o o o o H Cl HCl Formation of HCl
12. 13. <ul><li>Draw dot and cross diagrams for methane (CH 4 ), ammonia (NH 3 ) and nitrogen N 2 and carbon dioxide (CO 2 ) </li></ul>
13. 14. <ul><li>Elements in Group 1 form unipositive cations e.g. Na + </li></ul><ul><li>Elements in Group 2 form dipositive cations e.g. Mg 2+ </li></ul><ul><li>Elements in Group 3 form tripositive cations e.g. Al 3+ </li></ul><ul><li>Elements in Group 7 form uninegative anions e.g. Cl -1 </li></ul><ul><li>Elements in Group 6 form dinegative anions e.g. O 2- </li></ul>Formation of ionic bonds
14. 15. <ul><li>Na Cl </li></ul>x o o o o o o o Na + + Cl - NaCl
15. 16. <ul><li>Mg F </li></ul>x x o o F o o Mg 2+ + 2F - MgF 2 o o o o o o o o o o
16. 17. <ul><li>Draw diagrams to represent the ionic bonding for aluminium iodide and sodium oxide </li></ul>
17. 18. Properties of Ionic Compounds <ul><li>High mp/bp </li></ul><ul><li>Conduct electricity when molten or in aqueous solution </li></ul><ul><li>Dissolve in polar solvents (eg water) </li></ul><ul><li>Hard and brittle </li></ul><ul><li>React readily with each other in solution </li></ul>
18. 19. Covalent Compounds & Structures <ul><li>Covalent compounds may be classed as simple e.g water, ammonia, chlorine, sulphur dioxide, carbon dioxide </li></ul><ul><li>or as giant e.g. silicon dioxide (sand) diamond, graphite </li></ul>
19. 20. <ul><li>Simple covalent compounds are small molecules held together by Van der Waals forces only </li></ul><ul><li>Giant covalent structures are giant lattices where every atom is covalently bonded to many atoms </li></ul>
20. 21. Diamond Structure
21. 22. Properties of Simple Covalent Compounds <ul><li>Low mp/bp </li></ul><ul><li>Non conducting </li></ul><ul><li>Soluble in non-polar solvents </li></ul><ul><li>Solids are soft </li></ul>
22. 23. Properties of Giant Covalent Structures <ul><li>High mp/bp </li></ul><ul><li>Non-conducting (except graphite and some semiconductors e.g. silicon dioxide) </li></ul><ul><li>Non-soluble </li></ul><ul><li>Hard (except graphite) </li></ul>