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Unit 4 Atomic Theory and Structure. Periodic Table, Organization, and Properties. Groups vs Periods. ** Practice: Identify which two elements are most similar chemically: a. Mg Cs Zr Al Ca b. Cl Nb S Br Kr
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Groups vsPeriods • **Practice: • Identify which two elements are most similar chemically: • a. Mg Cs Zr Al Ca b. ClNb S Br Kr • Are the metals on the left or right side of the periodic table? • What are the group numbers for the transition metals?
Defining terms **Practice: What types of elements are malleable and ductile? What phase (solid/liquid/gas) are the majority of the elements in? Which group has elements that exist in all the phases? What is special about the noble gases? • Malleable • Ability to be hammered into sheets without breaking • Ductile • Ability to be stretched out into wires • Luster • Shininess
Atomic Radius (atomic radii): What is it? The radius is ½ of the distance measured from the center of one atom to the center of an adjacent identical atom. What is the trend? (use the periodic table to draw arrows showing the general trend) Decrease across a period: due to the increased number of protons having a greater pull on the valence electrons as you move across: increases down a group as you are adding more energy levels
Ionization Energy: What is it? The amount of energy required to remove one outer-most (or Valence) electron. What is the trend? (use the periodic table to draw arrows showing the general trend) Increase across a period: becomes the atom is more tightly held together as the valence sublevels become full: decreases down a group: you have more energy levels, the outer most electrons are further away and aren’t held on as tight
Electronegativity: What is it? What is the trend? (use the periodic table to draw arrows showing the general trend) The attraction an atom has to on a nearby electron: the closer an atom is to 8 valence electrons the higher the electronegativity Increases across a period: valence electrons get closer to 8): decrease down a group: because valence electrons get further from the nucleus
Ionic Radius (Ionic Radii): What is it? Size of an atom’s ion. The ion form is a different size than the neutral form What is the trend? (use the periodic table to draw arrows showing the general trend) Ionic radius decreases as a cation and increases as an anion. Ionic radius increases as you go down a group
Electronegativity **Practice: • Which atom/element is larger? Rb or Pb • What is the largest element? • What is the most electronegative element? • How is ionic radius different from atomic radius? • Which element has a higher ionization energy? K or Ga • Which element has a higher ionization energy? Li or Rb • How are electronegativity and ionization energy are related? What is the pattern between these two trends? Electronegativity
What is an atom? Smallest amount of substance that we can have that will still retain all the features of that substance Basic unit of matter: Fundamental unit of chemistry:
John Dalton: Proposed: all elements are composed of very small particles called atoms which are indivisible. (2) Proposed: All atoms of the same elements are identical. (3) Proposed: Atoms of different elements are different. (4) Proposed: Atoms of different elements can combine with each other only in simple whole number ratios to form compounds. (5) Proposed: Chemical reactions occur when atoms are separated, joined or arranged. However, atoms of one element ARE NOT changed into atoms of another element by a chemical reaction. (Only by nuclear reactions)
JJ Thompson What did he discover? With what experiment? What was his proposition and was it true? How did the cathode ray tube experiment prove that electrons exist and they are negative? Electrons are negatively charged + magnetic field - Magnetic field Cathode Ray Experiment Electron stream w/o applied magnetic field Electron stream after applied magnetic field electrons are negatively charged particles; very lightweight – their mass is considered negligible when describing the “mass of an atom” because they only weigh about 1/1839 the mass of a proton or neutron.
JJ Thomson (second proposition): What was Thomson’s second proposition? Is it true? Why or why not?? A plum pudding model—the protons and electrons were mixed together like a fruit salad (or plum pudding). The larger pieces of the “plum” were the protons swimming in a pudding of electrons
Ernest Rutherford: What was his proposition? What is true? What were the results of the gold foil experiment? Why were some of the particles deflected? The atom as mostly space and that all of the positive charge was located in a very small central nucleus. 1. Most particles went through (which is what was expected) 2. Some were slightly deflected 3. Some were deflected back and missed the fluorescent screen the positive alpha particles were hitting the positive, small, dense nucleus and getting deflected (since positive repels positive). Dense positive nucleus (meaning plum pudding was incorrect). Negative electrons were moving around the nucleus.
Niels Bohr: Proposed – Proposed - Electrons were in energy levels. The further an electron was from the nucleus, the higher its energy. the “planetary model” of the atom in which the electrons orbit the nucleus much as the planets orbit the sun.
Components of the Atom: Protons: Neutrons: Electrons: Atoms are always ________, meaning they have the same number of _________________. Atomic Number: Mass Number: Atomic Mass: Positively charged portion of the nucleus: P+ Portion of the nucleus that contains no charge, but contains the same mass as a proton: n very light negatively-charged particle which is found somewhere outside the nucleus. Its mass is considered negligible when determining the mass of an atom. It weighs only 1/1837 that of a proton, but its negative charge is as powerful as the positive charge of a proton. Shown as e‾. The number of protons found in the nucleus of an atom. Atomic number defines one element from another. It is the large whole number in the upper corner of the periodic table Number of protons plus neutrons found in the nucleus of an atom: Used to define isotopes An average of the masses of all the isotopes of that element, weighted by their percentage of abundance.
Isotopes: What are isotopes and how are they different? Example: Identify how many protons and neutrons are in the following group of isotopes Hyphen Notation is Name – Mass # Carbon-12 Carbon-13 Carbon-14 Changes in the number of neutrons and hence the mass number.
**Practice: Atoms and Isoptopes • What’s the difference between mass number and atomic mass? • How is the mass number calculated? • Where can the atomic mass be found? • How many protons are in sodium and how do you know? • How many electrons does a calcium atom have? How do you know? • What happens if the atomic number changes? • How many neutrons are in Uranium – 235? • What is the identity of an element with 3 protons, 4 neutrons and 3 electrons? • Write the hyphen notation for the element in #8.
Calculating Atomic Mass: Example: Naturally occurring chlorine is 75.53% chlorine-35 and 24.47% chlorine-37. What is the average atomic mass which should be placed on the Periodic Table for the element? Example: The element neon consists of three isotopes with masses of 19.99, 20.99 and 21.99 amu. These three isotopes are present in nature to the extent of 90.92%, 0.25% and 8.83% respectively. Calculate the atomic weight of neon **Practice: Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following atomic masses and abundances in nature: 6.017 amu at 7.30% and 7.018 amu at 92.70%.
Ions: What are they and how are they different? IF: #electrons < #protons (electrons are given or lost) then there is an excess ___________ charge and it’s called a _______________ IF: #electrons > #protons (electrons are gained) then there is an excess _____________ charge and it’s called an _______________
**Practice: Ions • The sulfide ion has a charge of ─2. How many protons and electrons does this ion have? • An element has 20 protons and 18 electrons. Identify the element and determine the ionic charge. • A magnesium ion has a +2 charge and a mass number of 25. How many protons, neutrons and electrons are there?
