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Halogens & Isotopes

Halogens & Isotopes. Today’s Lesson. Compounds of the Halogens Isotopes & Ar Our Experiment. Some Housekeeping. Our test will be on Friday 17 th of February. You will then change classes on the Monday. Next week – check your email for a practice test, study guide questions etc.

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Halogens & Isotopes

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  1. Halogens & Isotopes

  2. Today’s Lesson • Compounds of the Halogens • Isotopes & Ar • Our Experiment

  3. Some Housekeeping • Our test will be on Friday 17th of February. • You will then change classes on the Monday. • Next week – check your email for a practice test, study guide questions etc. • I’ll also be running after school help on the next two Wednesday’s in M301.

  4. Compounds of the Halogens • Compounds of the halogens are called Halides • Below is a simple example: • H2 (g) + Cl2 (g)  2HCl (g) • For Hydrogen Halides, they are always diatomic. This means that there it only contains 2 atoms. 1 Hydrogen and 1 Halogen atom.

  5. Properties of Halides • Below are some of the properties of Halides: • Hydrogen Halides are very soluble in water • Their solutions are acidic. Examples include: • Hydrochloric Acid (HCl) • Hydrobromic Acid (HBr) • Hydroiodic Acid (HI) • Sodium Chloride (NaCl) is also a Halide. It is an ionic compound and is held together in a giant lattice.

  6. More on Halides • Silver Halide • AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq) • These form precipitates which means they form solids. As uch, AgCl, AgBr, AgI etc all form precipitates or solids in water. • Fluorides are are normally toxic to humans, but small amounts are put in toothpaste to help strengthen teeth. • Potassium Iodide is commonly put in salt to stop people getting Goitres.

  7. Isotopes • The number of protons tells us the name of an atom. However, atoms can have a different number of neutrons. • An atom with a different number of neutrons is called an isotope • Isotopes are often radioactive and are likely to decay or break down • The amount of time it takes for half of the radioactive isotopes to decay is called a half-life

  8. Continued • Carbon 14 has a half life of 5730 years, so is often used to find the age of different objects under 50,000 years old. • It is hard for humans to work out the age of an object after 8 half lives. • Ar or RAM (Relative Atomic Mass) • The relative atomic mass of an element is the average mass of an atom. This help explains the atomic mass of Sodium (35.5!)

  9. Ar • Ar is the average mass of an atom. As there are different numbers of neutrons in some atoms of the same element, we average out the mass when possible. • RAM = (% X Mass Number of 1st Isotope) + (% X Mass Number of 2nd Isotope) +…. And so on. • We will now work out the Ar of Chlorine.

  10. Questions • Compounds of the Halogens (Page 100-101) Questions 1-5 • Isotopes & Ar (Page 14-15) Questions 1-6 • You can now complete your experiment. It will be due Wednesday 15thof February 2012.

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