Transcript electrons
INSIDE THE ATOM Three Topics: Section 1 • How scientists model the atom • What are charged particles • What were Rutherford’s experiments REVIEW VOCABULARY Matter: anything that has mass and takes up space. New Vocabulary anode • electrode with a positive charge electron cloud • region surrounding the nucleus in which electrons travel cathode • electrode with a negative charge neutron • particle in the nucleus of an atom that has the same mass as a proton and is electrically neutral alpha particle • fast-moving, positively charge bit of matter proton • positively charged particle present in the nucleus of all atoms • negatively charged particle located outside the nucleus of an atom • matter made up of only one type of atom electron element FIRST THOUGHTS • Summarize early ideas about the structure of matter • Matter was made of tiny particles and could be cut into smaller and smaller pieces until reaching a piece that could not be cut any more. • This smallest piece is an atom. Matter is made up of atoms Atoms cannot be divided into smaller pieces Dalton’s Ideas About matter All atoms of an element are exactly alike Different elements are made of different kinds of atoms Crooke’s Tube Mask Cathode - Shadow Anode + Crooke’s Experiments • He connected a battery to cathode (-) and anode (+) of a tube. He found that an object in the middle of the tube (mask) cast a shadow in a green glow. He concluded that the glow was caused by rays, or streams of particles. thomson’s experiments Rays are bent by magnet CATHODE RAYS MAGNET Thomson’s Experiments • He placed a magnet next to the tube. The ray was bent by the magnet, showing the ray was made of particles, not light. He envisioned an atom as a sphere of positive charge with negatively charged electrons spread out evenly within. This is sometimes called The Plum Pudding Model. rutherford’s experiment Rutherford’s Experiment • Experiment: Rutherford fired alpha particles at a thin film of gold. A screen lit up when it was hit by a charged particle. • Expected Result: Almost all the alpha particles would go straight through. • Actual Result: More particles bounced off than expected - some of them straight back! • Conclusion: Positive and negative charges not evenly spread out. Positive charge concentrated into a nucleus. Describe the following improvements to atomic theory. After Rutherford’s model, how How electrons are thought to the extra mass in the nucleus move in the most current atomic was explained model Neutron - neutral charge Electron Cloud The Atom Electrons + + + + Nucleus Protons Neutrons Electron Cloud The Atom particle location charge mass (relative) proton nucleus + 2000 neutron nucleus none 2000 electron electron cloud -- 1 Section 2: The Nucleus • What is radioactive decay? • What is half-life? • How are radioactive isotopes used? REVIEW VOCABULARY Atom: Matter is made up of atoms. New Vocabulary atomic number • number of protons in nucleus isotope • atom of an element with different number of neutrons mass number • number of neutrons plus number of protons radioactive decay • release of nuclear particles and energy • changing of one element into another through radioactive decay • high-energy electron that comes from the nucleus • amount of time it takes for half a sample of an element to decay transmutation beta particle Section 2: The Nucleus Carbon-12 Carbon-13 Carbon-14 Atomic number 6 6 6 Number of protons 6 6 6 Number of neutrons 6 7 8 Mass Number 12 13 14 Summarize what the strong nuclear force does. It holds the protons and neutrons in the nucleus. READING THE PERIODIC TABLE carbon Name 6 Atomic Number = # of protons, # of electrons C Symbol 12 Atomic Mass = # protons + # neutrons Sequence steps of radioactive decay The electron Neutron becomes unstable Neutron splits into electron and proton. The proton stays in the nucleus. is ejected with a large amount of energy. Atomic number increases by one. HALF-LIFE • You have 100 grams of Iodine-131, which has a half-life of 8 days. How much will be left after 24 days? 1 2 100 g 3 50 g 25 g 12.5 g Begin 8 days 16 days 24 days HALF-LIFE • You have 16 grams of Element-X, which has a halflife of 10 days. How much will be left after 40 days? 16 g Begin 1 8g 10 days 2 4g 20 days 3 2g 30 days 4 1g 40 days HALF-LIFE • You have 20 grams of Element-X, which has a halflife of 2 days. How much will be left after 6 days? 1 20g 2 10g 3 5g 2.5g 2 days 4 days 6 days Rate of Decay Time Elapsed Mass Start 1st 2nd 3rd HalfLife HalfLife HalfLife 0 days 8 days 16 days 24 days 20 g 10 g 5g 2.5 g half-life the amount of time it takes for one half of a substance to decay. Identify uses and hazards of radioactive material. USES Smoke detectors Medicine Date fossils Energy HAZARDS Radiation poisoning Radioactive Material Long half-life