Structure of an Atom

1. Structure of an Atom A brief review of the structure of atoms

2. History of Atomic Theory • See the Powerpoint on Atomic Theory Scientists for more information and pictures/models. • Review/Summary: • Democritus, 460 BC – proposes particles so small they can not be destroyed or divided, and describes them as “atomos” (uncuttable) • John Dalton, early 1800’s - first to use “atom”; proposes that atoms of the same element are identical, and atoms of different elements have different weights/masses; Solid Sphere Model • JJ Thomson, ~1897 – discovers the first subatomic particle, electrons; Plum Pudding Model • Ernest Rutherford, ~1912 – discovers the proton, and nucleus; Nuclear Model • Niels Bohr, ~1915 – discovers energy levels for the electrons; Planetary Model • Erwin Schrodinger, ~1926 – developed the Electron Cloud Model • James Chadwick, ~1932 – discovers the neutron in the nucleus • Most Modern Model – The electron cloud model with all three subatomic particles

3. Development of Atomic Theory • A more extensive review of Atomic Theory Development: • http://www.abcte.org/files/previews/chemistry/s1_p1.html Use the “next” button at the bottom of the webpage above to cycle through the different scientists and their theories/models.

4. What is an atom? • Smallest particle of an element (pure substance) that still has the properties of that element. • Most of the atom is made of EMPTY SPACE • Example: an atom of gold is the smallest particle of gold (an element or pure substance) that still has the properties of gold. • Video: http://www.youtube.com/watch?v=o-3I1JGW-Ck • Brainpop (username: sclee password: cougars): • Atom: http://www.brainpop.com/science/matterandchemistry/atoms/ • Atomic Model: http://www.brainpop.com/science/matterandchemistry/atomicmodel/

5. Two Main Regions of the Atom • Nucleus • Positive charge • Almost all of the mass of an atom • Tiny, dense center of the atom • Can be broken apart in chain reactions to produce HUGE amounts of energy for use in electricity, medicine, weapons, etc (nuclear energy) • Electron cloud • Negative charge • Almost 0 mass • Energy levels/shells • Max # electrons – 2,8,8* • Valence level – outermost energy level

6. The Nucleus of an Atom • Tiny and dense • Center of the atom • Contains protons and neutrons • Positive charge (positive protons plus neutral neutrons) • Very little of the volume (space) in an atom, but almost all of the mass • Mass = protons + neutrons • Units for mass are amu (atomic mass unit) • Held together by a strong nuclear force • Can be split apart in controlled chain reactions to release nuclear energy: • http://www.youtube.com/watch?v=ufEAg9h9wU8 • http://www.youtube.com/watch?v=mBdVK4cqiFs • Fermi is the first scientist to conduct controlled chain reactions • Nuclear energy in weapons: http://www.brainpop.com/science/energy/radioactivity/ • Video tutorial: http://www.youtube.com/watch?v=FSyAehMdpyI

7. Electron Cloud • Most of the volume in the atom, but almost 0 mass • Contains only electrons • Negative charge • Energy levels • Closest to the nucleus is the lowest level • Outermost level is the valence level

8. Subatomic Particles • Protons • Neutrons • Electrons • Video tutorial: http://www.youtube.com/watch?v=FSyAehMdpyI

9. Isotopes • Atoms of the same element can have different numbers of neutrons. • This means their mass is also different (mass = protons + neutrons) • Naming isotopes: use the name of the element, followed by the mass number of that atom • Ex: Carbon-12, Carbon-13 • Video Brainpop: • Isotopes: http://www.brainpop.com/science/matterandchemistry/isotopes/ • Radioactivity: http://www.brainpop.com/science/matterandchemistry/periodictableofelements/

10. Ions • In a neutral atom, the number of protons equals the number of electrons. • Neutral atoms are often unstable, because they do not have a full valence level. • Unstable atoms will gain or lose electrons to become stable. • Atoms which have gained electrons (gained negative particles) are negative ions. They will have more electrons than protons. • Atoms which have lost electrons (lost negative particles) are positive ions. They will have fewer electrons than protons. • To see if it is an ion, compare protons and electrons. • Video Tutorial Brainpop: • Ions: http://www.brainpop.com/science/matterandchemistry/ions/

11. Periodic Table Arrangement • Dimitri Mendeleev developed the first (near) modern Periodic Table of Elements • Page 71 in your book • Based on physical properties, especially atomic mass (later rearranged by atomic number) • Periods are rows, and tell how many energy levels the neutral atom has; elements increase left to right across the periods and are very different in properties/reactivity; • Groups or families are columns; atoms in the same group have the same number of valence electrons, and similar chemical reactivity.

12. Chemical Reactivity on the Periodic Table • Metals on the left (2/3 of the table), metalloids on the break, metals on the right (except hydrogen). • Most reactive metals – group 1, with 1 valence electron; • Most reactive nonmetals – group 17, with 7 valence electrons; • Nonreactive (inert) elements – group 18, with full valence level

13. Metals, Nonmetals, Metalloids on the Periodic Table

14. Periodic Table Trends Atomic Mass Increases Atomic number increases Atomic Mass Increases Atomic number increases Metallic Properties Increase