Grade_10_Unit_3_Atomic_Theory_(NXPowerLite) Opp

Grade_10_Unit_3_Atomic_Theory_(NXPowerLite) Opp - 100s of...

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1 100’s of free ppt’s from www.pptpoint.com library
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2 History of the atom Democritus (400 BC) suggested that the material world was made up of tiny, indivisible particles atomos , Greek for “uncuttable” Aristotle believed that all matter was made up of 4 elements, combined in different proportions Fire - Hot • Earth - Cool, heavy • Water - Wet Air - Light The “atomic” view of matter faded for centuries, until early scientists attempted to explain the properties of gases
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3 Re-emergence of Atomic Theory John Dalton postulated that: 1. All matter is composed of extremely small, indivisible particles called atoms 2. All atoms of a given element are identical (same properties); the atoms of different elements are different
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4 3. Atoms are neither created nor destroyed in chemical reactions, only rearranged 4. Compounds are formed when atoms of more than one element combine A given compound always has the same relative number and kind of atoms
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5 Atoms are divisible! By the 1850s, scientists began to realize that the atom was made up of subatomic particles Thought to be positive and negative How would we know this if we can’t see it or touch it?
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6 Cathode Rays and Electrons Mid-1800’s scientists began to study electrical discharge through cathode-ray tubes. Ex: neon signs » Partially evacuated tube in which a current passes through » Forms a beam of electrons which move from cathode to anode » Electrons themselves can’t be seen, but certain materials fluoresce (give off light) when energised
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7 JJ Thompson observed that when a magnetic or electric field are placed near the electron beam, they influence the direction of flow opposite charges attract each other, and like charges repel. The beam is negatively charged so it was repelled by the negative end of the magnet
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8 The JJ Thompson Model Thompson understood that all matter was inherently neutral, so there must be a counter
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Grade_10_Unit_3_Atomic_Theory_(NXPowerLite) Opp - 100s of...

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