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The Structure of the Atom. By: Ms. Buroker. Early Theories of Matter. The philosophers …. Many concluded that matter was composed of things such as earth, water, fire, and air Also, commonly accepted, was the idea that matter could be endlessly divided into smaller and smaller pieces.
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The Structure of the Atom By: Ms. Buroker
Early Theories of Matter The philosophers …. Many concluded that matter was composed of things such as earth, water, fire, and air Also, commonly accepted, was the idea that matter could be endlessly divided into smaller and smaller pieces.
Democritus (460 – 370BC) He was the first person to propose the idea that matter was not indefinitely divisible. “atomos” –atom: believed that atoms could not be created, destroyed, or further divided His ideas were rejected because he could not explain how they were held together.
John Dalton (1766 -1844) Marks the beginning of atomic theory revived and revised Democritus ideas …. “Dalton’s Atomic Theory” • Elements are made of tiny particles called atoms. • All atoms of a given element are identical. • The atoms of a given element are different from those of any other element.
Dalton’s Atomic Theory Continued … 4.) Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms 5.) Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.
The Atom The atom is the smallest particle of an element that retains the properties of that element.
Atoms Are Not the SmallestParticle of Matter In Thomson’s experiments, the rays always behaved the same regardless of what element was used for the gas or cathode. The particles making up these rays seemed to be a common denominator for all elements. Since atoms differed from element to element, this common denominator must be an even more fundamental particle than the atom.
Thomson’s “Plum Pudding” Model The particles making up the rays acted as if they were negatively charged. Since elements are neutral, there must be positive particles balancing out the particles. Thomson theorized that an atom consisted of a “pudding” of evenly distributed positive and negative particles.
Some Conclusions Then …. Most particles flew right through the foil as if there were nothing there. The foil was mostly empty space. A small number of particles were bounced back to their source. There must be a small, dense nucleus with a positive charge.
The Rutherford Model of the Atom A dense, positively-charged nucleus Negatively-charged electrons orbiting the charged nucleus However, this was not the end of the story.
Niels Bohr: 1913 *studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.
Bohr’s Atom electrons in orbits nucleus
HELIUM ATOM Shell proton N + - + N - neutron electron
ATOMIC STRUCTURE Particle Charge Mass proton + charge 1 neutron No charge 1 electron - charge nil
How Do Atoms Differ? Atomic Number After Rutherford’s gold foil experiment, Henry Mosley discovered each element contained a unique positive charge. The number of protons in an atom is referred to as the element’sAtomic Number Atoms are neutral, so:# of protons = # of electrons = atomic #
ATOMIC STRUCTURE He 2 Atomic number the number of protons in an atom 4 Atomic mass the number of protons and neutrons in an atom number of electrons =number of protons
Isotopes and Mass Number Mass Number = represents the # of protons and neutrons in an atom # of neutrons = mass number – atomic # Isotopes= atoms of the same element that differ in mass or atoms that differ in their number of neutrons.
How we represent Isotopes …. Potassium -39 Potassium -40 Potassium -41 39K 40K 41K
Atomic Mass Extremely small masses in scientific notation are difficult to work with … so a method was developed of measuring mass based on a standard. Amu = 1/12 the mass of a carbon -12 atom Atomic Mass = Average of all isotopes and their relative amounts.
Let’s Practice Given the following data, calculate the atomic mass of unknown element X. Then, identify the unknown element, which is used medically to treat some mental disorders.
Try this one… Calculate the atomic mass of germanium.
Can we count individual atoms or obtain their mass? • Chemists need a convenient method for counting accurately the number of atoms, molecules, or formula units in a sample of a substance. • The mole, commonly abbreviated mol, is the SI base unit used to measure the amount of a substance.
The MOLE • A mole of anything contains 6.02 x 1023 representative particles. • A representative particle is any kind of particle such as atoms, molecules, formula units, electrons, or ions. • 6.02 x 1023 is called Avogadro’s number
The Mole The mole is based on how many atoms are in a sample of 12-Carbon. In 12g of 12-Carbon, there are exactly 6.022 x 1023 atoms of carbon.
Let’s Make it Simple We have a term known as: MOLAR MASS OR FORMULA WEIGHT What that means to you … The molar mass of any element is equal to its atomic mass (in grams) … that mass contains 6.022 x 1023 atoms!! So … The molar mass is the mass of one mole of any pure substance!!
Radioactivity Nuclear Reactions are ones that involve an atom of one element changing into an atom of another element. Radioactivity is the phenomenon of rays being produced spontaneously by unstable atomic nuclei. Radioactive Decay is when unstable nuclei lose energy by emitting radiation in a spontaneous process.
Deflection • The effect of an electric field on three types of radiation is shown.
Types of Radiation Each contains 2 protons and 2 neutrons
Fission and Fusion • Nuclear Fission – splitting the nucleus into fragments • Releases large amounts of energy!! • Nuclear power plants use fission to generate power • Nuclear Fusion is the combination of nuclei … requires large amounts of energy!!
