Atoms!!!!. Chapters 4.1, 5.1, 4.2, 4.3, 4.4, 4.5. What are Atoms?. Atoms are very tiny particles that form the building blocks for all matter. Just What Size Is an Atom?. Let’s do a little exercise!!. What you’ll need A strip of paper A pair of scissors. DON’T DO THIS YET!
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What are Atoms? Atoms are very tiny particles that form the building blocks for all matter
Just What Size Is an Atom? Let’s do a little exercise!! • What you’ll need • A strip of paper • A pair of scissors • DON’T DO THIS YET! • Here is what to do … • Take your strip of paper and cut it into equal halves • Cut one of the remaining pieces of paper into equal halves • And so on …
Atom Facts • A sheet of paper is about 10,000 atoms thick • There are about 2,000,000,000,000,000,000,000 (that’s 2 thousand billion billion) oxygen atoms in a small drop of water. There are twice that many hydrogen atoms.
Objectives • I will know where metals, nonmetals and inert gases are found on the periodic table. • I will know that each element has a specific number of protons in the nucleus and that this is the same as the atomic number.
Objectives • I will know what an isotope is and that isotopes of an element have a different but specific number of neutrons in the nucleus. • I will know that substances can be classified (sorted) by their properties such as melting points, densities, hardness, thermal conductivity (how well heat travels through the substance) and electrical conductivity (how well electricity travels through the material).
Development of the Atomic Theory • The development of the modern atomic theory shows how a theory is based on experimental evidence, but is modified, as more evidence is collected.
Development of the Atomic Theory • The 1st people to think about the nature of matter were the Greeks in 430 B.C. • Democritus proposed that the idea of matter is formed of small pieces that could not be cut into smaller parts. • He used the term atomoV (atomos) which means “uncuttable” for the small pieces.
Democritus • He also thought that sweet tasting objects have smooth atoms, sour tasting objects have sharp atoms • In modern terms, an atom is the smallest particle of an element. Weird “Nothing exists but atoms and empty space, everything else is opinion ---”
Atomic Theory Continued… • Atomic theory grew as a series of models that developed from experimental evidence. As more evidence was collected, the theory and models were revised. • Many scientists were involved in the development of the atomic theory. • John Dalton • J.J. Thomson • Ernest Rutherford • Niels Bohr
John Dalton • John Dalton (1766-1844) • British School Teacher • First to do research on color blindness (he was color blind) • Did independent research in his laboratory
John Dalton • John Dalton was an English chemist and inferred that atoms had certain characteristics. • Dalton’s ideas included: • All elements are composed of atoms that cannot be divided. • All atoms of the same element are exactly alike and have the same mass. • An atom of one element cannot be changed into the atom of a different element. • Atoms cannot be created nor destroyed in any chemical reaction, only rearranged. • Every compound is composed of atoms of different elements, combined in a specific ratio.
J.J. Thomson • In 1897, J.J. Thomson (another English scientist) found that atoms contain negatively charged particles (electrons). • Thomson also proposed, based on other’s experiments, that atoms must also contain some sort of a positive charge. • Thomson describes an atom that consists primarily of negative charges scattered throughout a ball of positive charge (like raisins in a muffin, or plums in pudding).
Ernest Rutherford • Ernest Rutherford was a student of J.J. Thomson. • In 1911, Rutherford, with the help of his research team aimed a beam of positively charged particles at a thin sheet of gold foil. • He predicted that the charged particles would pass through the gold foil in a straight line, however he noticed that some of the particles were deflected strongly! • Rutherford inferred from this that an atom’s positive charge (protons) must be clustered in a tiny region in its center, called the NUCLEUS!
Rutherford’s Gold Foil Experiment • Rutherford was surprised that a few particles were deflected strongly. This led him to propose an atomic model with a positively charged nucleus.
Niels Bohr • In 1913, Niels Bohr, a Danish scientist, showed that electrons could have only specific amounts of energy causing them to move in certain orbits (similar to how the planets orbit the sun).
