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Atom. Chapter 14.

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  1. Atom Chapter 14

  2. I can identify the properties of the three subatomic particles of atoms.I can use a model to represent the structure of an atom and identify the forces that hold the subatomic particles together. I can identify the number of subatomic particles based on the Periodic Table of Elements. Competency G – Properties of Matter

  3. Electric Charge • Electric Charge is a property of matter • 2 types of Electric Charge: positive or negative • Electric Charge holds atoms together • Opposite charges ATTRACT • Same charges REPEL

  4. Electric Charge • Matter is electrically neutral when positive and negative charges are EQUAL and total electric charge is ZERO

  5. History of the Atom Important Discoveries: 1. J.J. Thomson (1897) discovered electrons • He passed electricity through a gas and noticed smaller negatively charges particles were given off • He proposed negative electrons were sprinkled throughout positively charged atom

  6. History of Atom 2. Rutherford, Geiger and Marsden (1911) discovered atom was mostly empty space with dense core called nucleus • Gold Foil experiment – most atoms passed through gold foil

  7. Atomic Structure

  8. Atomic Structure • Protons and Neutrons are massive compared to electrons • Mass of nucleus determines mass of atom • 99% of atom’s mass in nucleus where protons and neutrons are located • Electron cloud is empty space around the nucleus • Electron cloud is 10,000 larger than nucleus – reason why atom is mostly empty space

  9. Forces inside Atoms • Electromagnetic Force: Attractive force between electrons (-) and protons (+) binding electrons to nucleus

  10. Forces inside Atoms • Strong nuclear force: force that holds nucleus together • Very strong • Attracts neutrons and protons to each other • Works at only extremely small distances

  11. Forces inside Atoms • Weak Force: force that will turn a single neutron outside the nucleus into a proton and electron • Weaker than electromagnetic force and strong nuclear force • Important when atoms break apart

  12. Forces inside Atoms • Gravity: force of gravity inside atoms is very weak because an atom does not have a large mass

  13. How to tell Different elements apart? • Different elements contain DIFFERENT numbers of protons • Atomic Number: number of protons • All atoms of same element have same number of protons in nucleus • Each element has unique atomic number

  14. Stable Atoms • Stable atoms are neutral atoms • In STABLE atom number of protons EQUALS number of electrons

  15. Different Atoms

  16. PROBLEM SOLVING • What is the atomic number of Helium? • How many protons are in Helium? • How many electrons are in Helium • What is the atomic number of Carbon? • How many protons are in Carbon? • How many electrons are in Carbon?

  17. Ions • Ions: atoms that have different numbers of protons than electrons • Ions have an electric charge • Positive charged ions: contain more protons • Negative charged ions: contain more electrons

  18. Isotopes • Isotopes: atoms of the same element that have different numbers of neutrons • Mass number: number of protons + number of neutrons • Represents everything in nucleus • Number of neutrons = mass number – atomic number

  19. Referring to Atoms • When referring to atoms, most scientists write the name of the atom and then the mass number of the atom • Example: Nitrogen - 14 or Nitrogen – 15 • Both have the SAME number or protons • Both have the SAME number of electrons • They have DIFFERENT numbers of neutrons

  20. Isotope Notation • For Isotope Notation, scientists write the symbol of the element • Superscripted next to the symbol is the mass number • Subscripted next to the symbol is the atomic number

  21. Isotopes of Hydrogen

  22. PROBLEM SOLVING • How many neutrons are present in an aluminum atom that has an atomic number of 13 and a mass number of 27?

  23. Radioactivity • Most elements have stable isotopes • Stable means nucleus stays together • Radioactive means nucleus is unstable and breaks apart because too many or too few neutrons • Radioactive isotope eventually changes into stable isotope • Radioactivity is a process in which the nucleus spontaneously emits particles as it changes into a more stable isotope

  24. Radioactivity • Radioactivity can change one element into a completely different element • Alpha Decay: when nucleus ejects 2 protons and 2 neutrons • Atomic number decreases by 2 • Mass Number decreases by 4 • Beta Decay: when a neutron splits into a proton and electron • Atomic number increases by 1 • Mass Number stays the same • Gamma Decay: How a nucleus gets rid of excess energy • Nucleus gives off gamma rays • Atomic Number and Mass Number stay the same

  25. Electrons – 14.2 • Atoms interact with each other through electrons • Example: Chemical bonds involve only electrons

  26. Light Spectrum • Almost all light you see comes from atoms • Spectrum: is aspecific pattern of colors given off by an element • Spectrum includes very specific colors or characteristics • Spectral line: individual color in a spectrum • Spectroscope: instrument that separates light into a spectrum

  27. Light • Energy level: allowed energies for electrons • Electrons must be in one energy level or another – not between levels • Electrons change energy levels by absorbing or emitting light • Light is given off when an electron moves from a higher energy level to a lower energy level

  28. Bohr Model • Neils Bohr: Danish physicist who proposed concept of energy levels • When an electron moves from a higher energy level to a lower one, the atom gives up the energy difference between the two levels • The energy comes out as different colors of light

  29. Electrons and Energy Levels • Electrons located in the Electron Cloud • Electron Cloud divided into energy levels • Electrons farther from the nucleus have more energy

  30. Energy Levels Rules for energy levels: • 1. energy of electron has to match 1 of the energy levels • 2. each energy level can hold a certain number of electrons • 3. when electrons are added to an atom, fill lowest empty energy levels first

  31. Energy Levels • 1st energy level: 2 electrons • 2nd energy level: 8 electrons • 3rd energy level: 8 electrons • 4th energy level: 18 electrons • 5th energy level: 18 electrons

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