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Atoms Miss Sauer’s 7th Grade Science Bill Nye: Atoms • https://www.youtube.com/watch?v=96JYhfd7-50 Atoms • All matter is made up of atoms. Atoms are matter. Atoms are the building blocks of • • • • • matter. Atoms are mostly empty space. All liquids, solids, gases, & plasmas are made up of these tiny particles. Atoms are extremely small. Atoms are so small that in just one drop of water, there are about six sextillion atoms (6,000,000,000,000,000,000,000). Atoms are the smallest particle into which an element can be divided and still be the same substance. Many scientists and philosophers have investigated and worked with ideas. Atoms • Atoms are composed of electrons, protons, and neutrons. • The nucleus of an atom is made up of protons and neutrons. • Electrons are the least massive particle of the atom and travel around the nucleus. • Protons are positively charged. • Neutrons have a neutral charge (no electric charge). • Electrons are negatively charged. Democritus • Greek philosopher who named the atom in 440 BC. • Said all atoms are small, hard particles made of a single material formed into different shapes & sizes. • He believed the atom was indivisible. • In Greek, atomos means indivisible. Democritus – Atom Drawing Aristotle • Lived from 384 to 322 BC. • Believed you would never end up with an indivisible particle. • (no such thing as a smallest particle) Aristotle – Atom Drawing John Dalton • Late 1700’s • All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed. • His atomic theory stated that all atoms of the same element are alike. All atoms of different elements are different. (If it’s not on the periodic table, it’s not an element) • Atoms join with other atoms to make a new substance (we call this molecules). Atoms together are called molecules. • He performed experiments, which Democritus did not do. • We believe most of this today, except today we know about subatomic particles. John Dalton – Atom Drawing J.J. Thomson • 1897 • Discovered there are small particles inside an atom using a Cathode Ray Tube; proved • • • • • • electrons exist. He called the negatively charged particles electrons. Created a model known as the Plum Pudding Model (his model of the atom resembled plum pudding). First subatomic particle discovered (the electron). Discovered the electrons. Negatives have to equal the positives. Repeated the experiment to make sure it was right (same results each time). J.J. Thomson – Atom Drawing Cathode Ray Tube • Cathode Ray Experiment • https://www.youtube.com/watch?v=_nLESblUAHY Plum Pudding Model • Thomson's Plum Pudding Model of the Atom • https://www.youtube.com/watch?v=JUJPyQtoB5E Ernest Rutherford • 1909 (Former student of Thomson). • Through the Gold Foil Experiment he created a new atomic theory. • He aimed positive particles at gold foil coated with zinc sulfide, a substance that glowed when struck by particles. • He discovered the dense and positively charged region known as the nucleus. • Concluded that the atom is mostly empty space with a dense core (the nucleus). Ernest Rutherford – Atom Drawing Gold Foil Experiment • Gold Foil Experiment • https://www.youtube.com/watch?v=zUtIrO3fUgg Results of the Gold Foil Experiment 1. 2. 3. 4. 5. The discovery of the nucleus The nucleus is positively charged Most of the mass is concentrated in the nucleus The nucleus is tiny compared to the atom as a whole The atom is mostly empty space Niels Bohr • • • • 1913 Stated the electrons travel around the nucleus in definite paths. He thought of the electrons as rungs on a ladder. That electrons stood only on the steps, not in between) Niels Bohr – Atom Drawing The Modern Theory: • • • • Electrons are likely to be found in regions in between. These regions are called the electron cloud. Electrons follow the paths described in Bohr’s Model. Electrons are not in a fixed position; they are somewhere in the electron cloud. The Modern Theory – Atom Drawing Timeline 440 BC Democritus names the atom 384 to 322 BC Aristotle does not believe there is a smallest particle Late 1700’s John Dalton conducted experiments and stated all atoms of the same element are alike 1909 Ernest Rutherford (Gold Foil Experiment) discovered the dense and positively charged region known as the nucleus 1897 J.J. Thomson (Plum Pudding Model & Cathode Ray Tube); Discovered electrons 1913 Niels Bohr stated the electrons travel around the nucleus in definite paths Present Modern Theory: electrons are not in a fixed position; they are somewhere in the electron cloud Parts of the Atom Electron Orbits • To determine the number of electrons that can be held in the first orbit (closest to the nucleus): Use this formula: 2n2 (where n is the level of the orbit) Sub in 1 for n, because we want to know how many electrons can fit in the first level of orbit. 2(1)2 First multiply the exponent, then multiply the parenthesis. 12 = 1 x 1=1, then 2(1) = 2 Electron Orbits • To determine the number of electrons that can be held in the second orbit: Use the same formula: 2n2 (where n is the level of the orbit) Sub in 2 for n, because we want to know how many electrons can fit in the second level of orbit. 2(2)2 First multiply the exponent, then multiply the parenthesis. 22 = 2 x 2 = 4, then 2(4) = 8 Electron Orbits • To determine the number of electrons that can be held in the third orbit: Use the same formula: 2n2 (where n is the level of the orbit) Sub in 3 for n, because we want to know how many electrons can fit in the third level of orbit. 2(3)2 First multiply the exponent, then multiply the parenthesis. 32 = 3 x 3 = 9, then 2(9) = 18 Electron Cloud • The size of the electron cloud determines the size of the atom. • The weighted average of the masses of all the naturally occurring isotopes of an element is called atomic mass. • Atomic Mass Unit (amu) is the SI unit used for the masses of atomic particles. Isotopes • • • • Have the same number of protons but different numbers of neutrons Share most of the same chemical properties. Share most of the same physical properties. Are NOT stable when radioactive. Forces on the Atom • Gravity: depends on the mass of objects and the distance between them. • Electromagnetic Force: holds the electrons around the nucleus. • Strong Force: counteracts the electromagnetic force so protons stay together in the nucleus. • Weak Force: plays a key role in neutrons changing into protons and electrons in unstable atoms. Parts of the Atom Parts of the Atom • Most of the mass of an atom is found in the central part of the atom called the nucleus. • • • • The nucleus of an atom is made up of protons and neutrons. These particles (protons & neutrons) are packed very tightly together in the nucleus. Electrons are found outside the nucleus. They circle the nucleus very, very quickly. Electrons are very small and have almost no mass. • The number of electrons in an atom is ALWAYS EQUAL to the number of protons in the nucleus of that atom. Parts of the Atom • • • • Protons have positive (+) charges. Electrons have negative (-) charges. Neutrons have no charges. They are neutral. Since atoms have the same number of protons and electrons, the number of positive charges equals the number of negative charges. The opposite charges cancel each other out. Therefore, the whole atom has no overall charge. • Protons determine the identity of the elements. APE APE Atomic Number = # of Protons = # of Electrons So, if the Atomic Number is 27, there are 27 Protons in the element, & there are 27 Electrons. All 3 are equal! Subatomic Particles Sub-Atomic Particle Mass in AMU’s Charge Location in Atom Protons 1 AMU + Inside the nucleus Neutrons 1 AMU 0 Inside the nucleus Electrons 1/1,840 = 0 AMU - In the electron cloud/outside the nucleus Electrons are not included in the atomic mass because they are so small. Ions • If an element turns into an ion, the number of electrons WILL NOT equal the number of protons. Positives will not equal the negatives. Atomic Mass Atomic Mass = Protons + Neutrons (Remember: Most of the mass is concentrated in the nucleus!) Elements • The first letter of an element is capitalized (upper case), the second letter is lower case. • Example: Fe • Elements are arranged on the periodic table according to their number of protons. • Elements are different because of the different number of protons in the nucleus. Look at the Periodic Table 8 Atomic Number O Symbol Oxygen Element Name 15.999 Atomic Mass Atomic Number & Atomic Mass ATOMIC NUMBER equals the number of PROTONS or ELECTRONS. ATOMIC MASS equals the number of PROTONS + NEUTRONS. Atomic Number & Atomic Mass ATOMIC NUMBER equals the number of PROTONS or ELECTRONS. Example: Boron, Atomic Number: 5; # of Protons: 5; # of Electrons: 5 ATOMIC MASS equals the number of PROTONS + NEUTRONS. Example: Boron, Atomic Mass: 10.81; # of Protons: 5 + # of Neutrons: 5.81 5 + 5.81 = 10.81 Closure Questions • Give elements and ask: atomic number, atomic mass, # of protons, # of electrons, & # of neutrons. • • • • • Parts of the atom (location, charge, mass). How to draw an atom of an element. How to write symbol for elements. Isotopes exist because? Figure out the # of protons given the atomic mass or atomic number.