The Building Blocks of Matter ATOMS The Building Blocks of Matter

History of the Atom Around 400 B.C. Democritus was the first person to use the term atom. Atom is from the Greek word “indivisible” 1704 Isaac Newton proposed a mechanical universe with small solid masses in motion 1808 John Dalton proposed his atomic theory based upon measurable properties of mass

Properties of Mass There are several basic laws which drive Atomic Theory Law of Conservation of mass Matter is never created nor destroyed during ordinary physical and chemical changes Law of Definite Proportions States that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound Law of Multiple Proportions If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

Dalton’s Atomic Theory In 1808, an English schoolteacher named John Dalton proposed an explanation for the different properties of mass. Reasoned that elements were composed of atoms and combine to form compounds

Daltons Atomic Theory All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged

Dalton’s WRONG!!!! We now know that atoms can be divided into smaller particles. An element can have atoms of different masses, called isotopes.

Structure of the Atom Nucleus Protons Neutrons Electrons 75047 Dense, positively charged center of the atom Composed of protons and neutrons Makes up the mass of an atom Protons Positively charged Neutrons No charge Electrons Negatively charged, located outside the nucleus Makes up the size of the atom 75047

Electrons In 1897, J.J. Thomson, using cathode ray tubes, found negatively charged particles called electrons https://www.youtube.com/watch?v=O9Goyscbazk In 1909, Robert Millikan measured the charge of the electron Oil drop experiment https://www.youtube.com/watch?v=XMfYHag7Liw

Plum Pudding Model Proposed by Thomson Negative electrons were spread throughout the positive charge of the atom Like plums in plum pudding, thus the name…get it He was wrong!!!

Glowing Matter Around 1900, Max Planck explained the phenomenon of hot glowing matter. Explained this using discrete units of energy he called “quanta” or “quantum” This idea would later be used to “correctly” place electrons in an atom.

Behold…The Nucleus In 1911, Ernest Rutherford found a dense, positively charged bundle of matter he called the nucleus Used the Gold Foil Experiment to find the nucleus https://www.youtube.com/watch?v=Zd6_zVdMgJk&feature=related https://www.youtube.com/watch?NR=1&v=kHaR2rsFNhg Nuclear forces are short range forces that hold protons and neutrons very close together

Rutherford’s Model Ernest Rutherford used his research to develop his own model of the atom Dense positively charged center, nucleus Electrons traveled around the nucleus in empty space He was Wrong!!!!

To see if someone got the correct model of the atom!!! STAY TUNED To see if someone got the correct model of the atom!!!

The Power of the Proton In 1914, H.G.J. Moseley using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote "The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.

The rest of the Nucleus In 1932, James Chadwick, using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron

Counting Atoms Atomic number (Z) is the number of protons an atom contains Change the number of protons, change the element Isotopes are atoms with the same number of protons but with varying numbers of neutrons Two was to symbolize isotopes, hyphen notation and nuclear symbol notation Mass Number is the total number of protons and neutrons in an atom Nuclide is a general term for a specific isotope of an element

Masses of Atoms Relative atomic mass uses units called “atomic mass units (amu)” An amu is defined as the 1/12th the mass of a carbon-12 atom Since a Carbon-12 atom contains 6 protons and 6 neutrons, 1 amu equals the approximate mass of either a proton or neutron Atomic Weight is the weighted average of atomic masses of all known isotopes The most abundant isotopes contribute more to the overall mass of the element