This means that there is a higher nuclear charge which increases the pull the nucleus has on the electrons. As you go right, the atomic numbers increase. Going from left to right on the periodic table, the atomic radii get smaller. The atomic radius of an atom is the distance between an atom's nucleus and its valence electrons. When in doubt, think about nuclear charge and the periodicity of the periodic table. The best way to conceptualize this information is to think about it through the concepts we went over above. Let's try to apply the concepts above to the five periodic trends that you should learn and understand for the AP Chemistry exam. □ Want to read more about Coulomb's law? Check out this study guide on "Atomic Structure and Electron Configuration." 5 Periodic Trends to Know for AP Chemistry Effective nuclear charge is equal to the actual nuclear charge (Z) - the charge shielded by other electrons (S). You do not need to know this formula for the AP exam, but it may help you better understand nuclear charge. In order to accurately represent the nuclear charge of a nucleus, we must account for both the actual nuclear charge and the charge shielded by other electrons (S). Electrons are negatively charged, and the nucleus is positively charged.Įlectrons that are in the outer shells of an atom may be shielded by the innermost electrons because of the electron-electron repulsion present. In order to fully comprehend the forces electrons feel, remember that opposite charges attract. Let's now compare neon, the second noble gas in group 18, with xenon, the fifth noble gas. All noble gases are generally unreactive due to their high stability. For example, the elements in group 18 are called noble gases. Some groups on the periodic table have a name, since the elements in a single group have similar properties. In other words, these elements tend to have similar chemical properties. Because these elements all have the same number of valence electrons, they can bond to other elements in similar ways. □ Shared Properties: Every element in one group has the same number of valence electrons in its outermost shell. □ Properties that differ: One group on the periodic table is organized so that as you move down a group, the number of occupied electron shells increase. However, sodium has 11 protons (represented by its atomic number of 11), and argon has 18 protons (represented by its atomic number of 18). You could see here that both sodium and argon have a total of three occupied electron shells, following the pattern of elements in the same period. Let's compare sodium, which is the first element in period 3, with argon, the last element in period 3. □ Shared Properties: In each row, the elements have the same number of occupied electron shells. This trend contributes to the differing effective nuclear charge of elements in the same group, which we'll discuss below. The atomic number, or the number of protons in an atom's nucleus, determines the basic chemical properties of said element. □ Properties that differ: Going horizontally, each period is organized in order of increasing atomic number. It is also important to note that the periodic table is divided into 18 columns (called groups) and 7 rows (called periods). It was purposely made to group chemicals of similar properties together. In order to fully understand why the trends occur the way they do, it's important to cover the following topics: Organization of the Periodic TableĪs mentioned before, the periodic trends aren't too difficult to grasp since they follow the chronology of the periodic table. Foundational Concepts for Periodic Trends A cool thing about the periodic table is that it is organized to demonstrate different trends and properties of elements that can be explained by the pattern of electron configurations and the presence of electron-filled orbitals. The periodicity of the periodic table, or its tendency to recur at intervals, can help you estimate the properties of atoms that haven't even been discovered yet.įor the sake of the AP Chemistry exam, rather than only understanding the trends, you should be able to explain why they happen.
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