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CHEM 1A03 UNIT 3: Periodic Trends Introduction

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CHEM 1A03 UNIT 3: Periodic Trends Introduction Hey! Thanks for opening up this Chemistry Periodic Trends Review! The education team at WebStraw McMaster has put together a comprehensive breakdown for you that covers all the key concepts for Chemistry Periodic Trends Members of our team have taken the course in previous years, and we understand better than anyone else what specific ideas and concepts tend to trip students up throughout the semester. We are essentially offering you the key takeaways from the course, after having completed the course ourselves. Before you read further, also keep in mind that these review packages are not meant to be a tool for you to learn the course from scratch. The content presented below was designed with the assumption that you already have a preliminary understanding of Periodic Trends. Our goal is to help give you a more in-depth understanding of key outcomes, as well as to help you see how concepts relate/connect to one another within the scope of the course as a whole. We do our best to cover every topic within the unit; however, some testable outcomes may not be discussed. With that said, best of luck in your studying! Remember to make good use of your time, but to also take breaks as well. Yousef Abumustafa & Julia Ma The WebStraw McMaster Chemistry team WebStraw McMaster Periodic properties of elements The periodic table is divided into called columns called groups that group elements with similar chemical/physical properties together and rows called periods that group elements with the same number of atomic orbitals together.1 ❖ There are 3 general sections in the periodic table: metals, non-metals, and metalloid Location on Rule Properties Periodic Table Located predominantly on - Have a tendency to lose electrons the left side of the easily periodic table - High melting point and density Metals - Typically solid at room temp (except Hg) - Good reducing agents Located in the top right - Have the tendency to accept side of the periodic table electrons - Can be solid, liquid, or gas at room Non-metals temp - Typically have higher electronegativity than metals Construct the “staircase” - Exhibit both metal and non-metal Metalloids that separates metals properties. from non-metals 1 Image from: https://www.angelo.edu/faculty/kboudrea/periodic/physical_metals.htm WebStraw McMaster Electron Screening/Shielding and Effective Nuclear Charge (Zeff ) As the name suggests, electron shielding refers to the process of electrons in the previous orbitals “shielding” the electrons in the valence shell from the nuclear charge aka. the attractive force of the nucleus (since the nucleus is positive). ❖ This affects the ability of the valence electrons to experience an effective nuclear charge Effective nuclear charge is the attraction force felt in the atom between the valence electrons and the protons located in the nucleus. ANALOGY: Think of the protons in the nucleus as celebrities, the electrons in core shells as bodyguards, and the valance electrons as crazy fans. The fans will try their best to get to the celebrities in the nucleus, but as we increase the number of bodyguards, their ability to do so is hindered. Group Period Zeff typically decreases as we Zeff typically increases as we move from Zeff Trend move down the periodic table. left to right on the periodic table. This occurs because electron This occurs because the electron shielding shielding increases down a effect remains constant across a period. group. The shielding effect is Across a period all the elements have the enhanced by increased core same number of inner-shell electrons, electron shells as the energy however, the number of protons increases Explanation levels increase down a group. from left to right of a period. Essentially, Thus there are numerically what this means is that there will be a more inner-shell electrons that greater amount of nuclear charge that can shield the valence electrons be shared amongst the valence electrons from the proton force in the as the number of protons increase, which nucleus. will increase Zeff. WebStraw McMaster Atomic Radius The atomic radius is the radius of an atom that is measured from the nucleus to the outermost cloud of electrons.2 Group Period Atomic Radius Atomic radius tends to increase Atomic radius tends to decrease as as we go down the periodic table we go across a period. Trend As we move down the periodic Due to a decrease in nuclear charge table, we increase the number of across the periodic table, the atoms Explanation core electron shells and this possess a smaller radius. causes the increase in atomic radius. 2 Image from: https://ch301.cm.utexas.edu/section2.php?target=atomic/trends/atomic-radii.html WebStraw McMaster Ionic Radius The Ionic radius is a similar concept to that of the atomic radius, however it is when the atom is in its ion form. As a general rule of thumb, cations will be smaller than their parent atom whereas anions will be larger. These features are due to electronic repulsion forces which are more prominent in anions when compared to their parent atoms (since they contain more electrons) and vice versa for cations.3 Cations Anions Generally, the ions get Anions tend to get larger the closer they smaller the closer they are are to the metalloid line and when Trend to the metalloid line and moving down the periodic tab get larger when moving down the periodic table. 3 Image from: https://chem.libretexts.org/Courses/Bellarmine_University/BU%3A_Chem_103_(Christianson)/Phase_3%3A_ Atoms_and_Molecules_- _the_Underlying_Reality/8%3A_Periodic_Trends_in_Elements_and_Compounds/8.2%3A_Atomic_and_Ionic_Radi us WebStraw McMaster Ionization Energy The Ionic radius is a similar concept to that of the atomic radius, however it is when the atom is in its ion form. As a general rule of thumb, cations will be smaller than their parent atom whereas anions will be larger. These features are due to electronic repulsion forces which are more prominent in anions when compared to their parent atoms (since they contain more electrons) and vice versa for cations. Group Period Ionization IE decreases as you go down a group IE increases as you go from Energy Trend left to right on a period This is the case because as we go down As you go across the periodic the periodic table, atoms increase in the table, the number of number of electron shells they have. electrons is increasing but Explanation Since the VE are now further from the the number of shells remains nucleus (positive charge), they are much the same. easier to remove from the atom. Elements typically have three levels of ionization energy. These levels indicate how much energy is required to remove the first, the second, and the third valence electrons. Usually, as you increase the ionization level, so does the amount of energy required to remove the electron. WebStraw McMaster Electron Affinity Electron affinity is the amount of energy that is released when a gaseous atom gains an electron. It can be thought of as a measure of attraction that an element has to towards an electron Group Period Electron EA decreases as you go down a group. EA increases as you go from left to right on a period. Affinity Trend When moving down a group, the As you move towards the right atomic radius increases, due to this of the periodic table, the atoms increase in size, an added electron will require electrons to complete be further from the atom's nucleus. their octet and become stable. Explanation Therefore, because of this increased Due to the gravitation towards distance, the force of attraction a stable state, these elements between the negative electron and are heavily attracted to positive nucleus is weakened. electrons Exception to trend Noble gases have no desire at all to gain an extra electron as they already have completely filled orbitals. Gaining an electron would throw the atom's stability off, putting it in an extremely unstable state. Electronegativity Electronegativity is the measure of an element to attract a pair of electrons that are shared in a covalent bond. This value is usually provided for each element on the periodic table. It flows the typical trend that we have seen numerous times above: decreases down the periodic table and increases going from left to right on the periodic table. NOTE: fluorine is the most electronegative element in the periodic table. WebStraw McMaster Summary Table The Trend What is it? Trend on periodic table Effective nuclear Attraction force felt between Typically increases as we move charge the valence electrons and the from left to right protons in the nucleus. Atomic radius The distance from the nucleus increases as we go down the to the outermost cloud of periodic table and decrease as electrons. we go across it (left to right) Ionization energy Minimum energy required to increases when going from left remove the valence electron to right and decreases as you go from a gaseous atom. down a group Electron affinity Amount of energy that is increases when going from left released when a gaseous atom to right and decreases as you go gains an electron. down a group Electronegativity Measure of an element to This value is usually provided for attract a pair of electrons in a each element on the periodic covalent bond. table WebStraw McMaster Assad.4 4 Image from: https://sciencenotes.org/periodic-table-trends/ WebStraw McMaster Practice Questions 1. Which of the following describes properties of a metallic element? I. Located on the left side of the periodic table II. Has a low boiling point III. Tends to be oxidized a. I, II b. II, III c.
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