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Atoms and the Periodic Table

Learn about the atomic structure, including the ideas proposed by Democritus and John Dalton. Explore the components of an atom - protons, neutrons, and electrons, and understand their charges and positions. Discover the different models of the atom, including the Bohr model. Review and compare key concepts in atomic structure.

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Atoms and the Periodic Table

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  1. Atoms and the Periodic Table Atomic Structure

  2. What are atoms? • Democritus • 4th century B.C.; Greek philosopher • Suggested that the universe was made of invisible units called atoms – “unable to be divided”. • Believed movement of atoms caused the changes in matter he observed. • Didn’t have the evidence needed to support existance of atoms. • John Dalton • 1808; English schoolteacher • Proposed his own atomic theory • Much evidence

  3. Dalton’s Theory • Every element is made of tiny, unique particles called atoms that cannot be subdivided. • Atoms of the same element are exactly alike. • Atoms of different elements can join to form molecules.

  4. What’s in an Atom? • Atoms are made of protons, neutrons, and electrons: • Nucleus – center of each atom. • Carries an overall positive charge. • Proton – a positively charged subatomic particle in the nucleus of an atom. • Neutron – a neutral subatomic particle in the nucleus of an atom. • Electron – a tiny negatively charged subatomic particle moving around outside the nucleus of an atom.

  5. Atoms have no overall charge. • A helium atom has two protons and two electrons. • The atom is neutral because the positive charge of the two protons cancel the negative charge of the two electrons. • Charge of two protons: +2 • Charge of two neutrons: 0 • Charge of two electrons: -2 • Total charge of a helium atom 0

  6. Models of the Atom • Bohr model • Niels Bohr – 1913; Danish scientist. • Suggested electrons in an atom move in set paths around the nucleus. • Much like planets orbit the sun in our solar system. • Energy levels – any of the possible energies an electron may have in an atom. • Gain energy to move to a higher level • Lose energy to move to a lower level

  7. Electron Facts • Electrons behave more like waves on a vibrating string than like particles. • It is impossible to determine both the exact location of an electron in an atom and its speed and direction. • Calculating the change or probability. • Electron cloud – whole shaded area of model • Orbitals – regions in an atom where electrons are found. • Valence electrons – outermost electrons.

  8. Atomic Structure Review 3.1 • Draw and label the parts of a helium atom. Include the mass and charge of each subatomic particle. • Describe the three main ideas of Dalton’s atomic theory in your own words. • Compare the outermost electrons of an atom with the inner electrons of an atom in terms of energy. • Compare the positions of the electrons in Bohr‘s model of the atom with their positions according to modern atomic theory.

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