Teacher Instructions: • • Go to www. Brainpop. com Login: edhpop Password: edhpop 1 Go to Science Go to “Matter and Chemistry” Go to “Atoms” view video Have students complete quiz (graded) as a class, then go through the powerpoint. Have students define protons, neutrons and electrons on the page that they will complete the table on slide 13. • Students must turn table and definitions in to their science teacher. Atoms, Molecules, and Ions
Basic Atomic Structure
EARLY THEORIES Democritus’s 460 – 370 B. C. • Matter is composed of empty space through which atoms move. • Atoms are solid, homogeneous, indestructible, and indivisible. • Different kinds of atoms have different sizes and shapes. • The differing properties of matter are due to the size, shape, and movement of atoms. • Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves.
Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early 19 th century, championed by John Dalton.
Dalton’s Postulates • • Each element is composed of extremely small particles called atoms. All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.
The Electron • Streams of negatively charged particles were found to emanate from cathode tubes. • J. J. Thompson is credited with their discovery (1897).
Millikan Oil Drop Experiment Robert Millikan (University of Chicago) determined the charge on the electron in 1909 [ – 1] and he calculated the mass of an electron [9. 1 × 10 -28 g].
The Atom, circa 1900: • “Plum pudding” model, put forward by Thompson. • Positive sphere of matter with negative electrons imbedded in it.
Discovery of the Nucleus Ernest Rutherford shot particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.
The Nuclear Atom Since some particles were deflected at large angles, Thompson’s model could not be correct.
THE NUCLEAR MODEL According to Rutherford, most of the atom consists of electrons moving rapidly through empty space and a very dense, positively charged nucleus.
Other Subatomic Particles • By 1920 , Rutherford had refined his concept of the nucleus: He concluded that the very dense nucleus contained positively particles called protons. • James Chadwick, a coworker, showed that the nucleus also contained a neutral particle in 1932. This was the neutron – a particle with nearly equal mass as a proton.
Properties of Subatomic Particles Relative Actual mass Particle Symbol Location Charge mass (g) 1– 1 1840 9. 11× 10 -28 Nucleus 1+ 1 1. 673× 10 -24 nucleus 0 1 1. 675× 10 -24 Electron e- Around nucleus Proton p+ Neutron n 0
Atomic Structure and the Periodic Table Symbol Name 14 Si 28. 086 Silicon Atomic number = # protons & # electrons (if neutral atom) Atomic Mass: Round to a whole #: 28 = Relative mass of nucleus -14 = # protons 14 = # neutrons
Practice From the Periodic Table Complete the following chart: Name Symbol Relative # # # protons mass neutrons electrons Lithium Mg 26 16