Chemistry Final Revision PDF

Chemistry Final Revision Created by: Ibrahim 10A Modern Atomic Theory Investigation 1 Experience 4  What is the Quantum Mechanical Model? The quantum mechanical model is like the Bohr model in that the energies of electrons are restricted to certain values. The quantum mechanical model,...

Chemistry Final Revision Created by: Ibrahim 10A Modern Atomic Theory Investigation 1 Experience 4  What is the Quantum Mechanical Model? The quantum mechanical model is like the Bohr model in that the energies of electrons are restricted to certain values. The quantum mechanical model, however, does not specify an exact path for electrons moving around the nucleus. For each energy level, there is a region of space, called an atomic orbital, where there is a high probability of finding an electron.  What is the shell model? The shell model consists of orbitals with different letters and energy levels which are: S: Holds up to 2 electrons and has 1 orbital P: Holds up to 6 electrons and has 3 orbital D: Holds up to 10 electrons and has 5 orbital F: Holds up to 14 electrons and has 7 orbital (Note: Each orbital holds a maximum of 2 electrons)  How to write electron configuration using crazy arrows? You can write electron configurations of any element using the crazy arrows, you follow the arrows in a certain sequence to model your electrons, and you stop when you have wrote the configuration which is enough for the number of electrons you have. Example: Argon (18 Electrons) 1s2, 2s2, 2p6, 3s2, 3p6 I stopped at 3p6 because I have 18 electrons and  How to calculate the amount of valence electrons? You can identify valence electrons of an element depending on which group it belongs to. If an element is in group 1, it has one valence electron. If an element is in group 2, it has two valence electrons. If an element is in group 14, it has four valence electrons. (group number -10) If an element is in group 15, it has five valence electrons.(group number -10) If an element is in group 16, it has six valence electrons.(group number -10) If an element is in group 17, it has seven valence electrons.(group number -10) If an element is in group 18, it has eight valence electrons.(group number -10) (Excluding Helium, which has 2) Groups 3 to 12, not able to tell. (Transition metals) Electrons in Atoms Investigation 1 Experience 5  What is the Lewis Dot Structure? The Lewis Dot Structure is used to model the valence electrons of an element. By writing the symbol of the element and placing a dot in each side of the symbol for each valence electron until all valence electrons are finished.  What is the Orbital Notation? The orbital notation is used to model the electron configuration using arrows (to represent electrons) and squares (To represent orbitals). s has 1 square, p has 3, d has 5, and f has 7. Also, there are 3 main rules to always follow: Hund’s Rule and Pauli’s Exclusion as well as Aufbau’s principle.  Hund’s Rule and Pauli’s Exclusion Hund's Rule states that electrons will Pauli’s exclusion principle states that no occupy degenerate orbitals (orbitals two electrons in an atom can have the with the same energy) singly and with same set of four quantum numbers. This parallel spins before pairing up. This principle ensures that each electron occupies a unique quantum state, leading minimizes electron repulsion and to the distinct electronic configurations of stabilizes the atom. Essentially, it’s like atoms. Essentially, it’s like assigning kids choosing their seats on a bus—they unique seats at a concert—no spread out before doubling up. double-booking! Electrons spin in opposite directions in the same orbital to avoid repulsion. Hund’s Rule and Pauli’s Exclusion Aufbau Principle It states that electrons have to be distributed in the orbitals with low energy first then higher ones. (Follow the crazy arrow sequence.)  What is the noble gas notation? The noble gas notation is just like the electron configuration but summarized. How to write it? Identify the nearest noble gas: Find the noble gas that comes before your element in the periodic table. Write the symbol for that noble gas in brackets: This represents the core electrons. Continue with the electron configuration: Start from the noble gas and add the remaining electrons to complete the configuration.  Example For example, for calcium (Ca): The nearest noble gas before calcium is argon (Ar). Write [Ar]. Calcium's electron configuration continues from argon with 4s². So, the noble gas notation for calcium is [Ar] 4s2 (Note: If you don’t know where to start after writing the noble gas, each noble gas has its own start. Example, if the noble gas is helium you start with 2s2, if it’s neon you start with 3s2, and the continue.) The Periodic Table: An Overview Investigation 2 Experience 1  Development of the Periodic Table In the late 1700s and 1800s scientists began to organize the known elements based on their properties. Many different scientists across the globe are credited with making contributions to the development of the periodic table. One of those scientists was the Russian chemist Dmitri Mendeleev.  Dmitri Mendeleev In 1869 and 1871, Russian chemist Dmitri Mendeleev published and then revised a table using known patterns. He arranged the elements by atomic mass but sometimes broke this rule to group elements with similar properties together. For example, he placed tellurium (atomic mass of 127.60) before iodine (atomic mass of 126.90) so that iodine could be in the same group as bromine.  The Modern Periodic Table Each horizontal row of elements in the periodic table is a period. The properties of elements change as you move across a period. But the pattern of properties within a period repeat from one period to the next. This pattern gives rise to the periodic law which states that when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. Each vertical column of elements is a group. Elements in the same group have similar physical and chemical properties.  The 3 main categories of the periodic table Metals Non-Metals Metalloids  Metals Metals are shiny and, except for mercury, solid at room temperature. They conduct heat and electricity and are malleable and ductile. Malleability: It corresponds to a change of metal into sheets. Examples: gold, silver and aluminum. Ductility: It corresponds to a change of metal into wires. Examples: copper, bismuth and nickel.  Non-Metals Nonmetals may be solids, liquids, or gases. When in a solid state, they are brittle. They are poor conductors of heat and electricity. Most nonmetals are gases at room temperature. Five nonmetals (carbon, phosphorous, sulfur, iodine, and selenium) are solids and bromine is a liquid.  Metalloids Metalloids have properties of both metals and nonmetals. Some metalloids are shiny like metals, and some are not. Like nonmetals, the metalloids are brittle. They are poor conductors of electricity and heat but may be used as semiconductors under certain conditions. Pure silicon is a poor conductor of electricity, however, mixing silicon and boron together produces a good electrical conductor. Such mixtures make excellent computer chips and are the basis for semiconductors and the consumer electronics industry. The ability to manipulate conductivity is one reason semiconductors are used in many different devices. Investigation 2 Experience 2 & 3 The Periodic Table and Atomic Structure Periodic Trends  Atomic Radius Atomic Radius is half the distance between the nuclear of two identical atoms. It's influenced by the number of electron shells and the effective nuclear charge, which impacts how tightly electrons are held by the nucleus.  Atomic Radius Trend Atomic Radius (A.R) can increase or decrease across a period or down a group. Atomic Radius decreases when going across a period Atomic Radius increases when going down a group Trends across a period and down a group A.R ↓ A.R ↑  Effective Nuclear Charge AKA Zeff Zeff or effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. It is calculated by subtracting the atomic number (The number of protons) and the number of core electrons (Total number of electrons minus number of valence electrons) The result always has to have a positive sign before (eg: +2)  Effective Nuclear Charge/Zeff Trend Also, Zeff can increase or decrease when going down a group or across a period. Zeff increases across a period because the atomic number or the number of protons increases while the number of core electrons stays the same Zeff stays the same down a group because the core electrons increase while the valence electrons stays the same Trends across a period and down a group A.R ↓ Zeff ↑ A.R ↑ Zeff →  Examples of Calculating Zeff Across period 3 Down group 15 a) Na11 = 11 - (11 - 1) = +1 a) N7 = 7 - (7 - 5) = +5 b) Mg12 = 12 - (12 - 2) = b) P15 = 15 - (15 - 5) = +5 +2 c) As33 = 33 - (33 - 5) = +5 c) Al13 = 13 - (13 - 3) = +3  Shielding Effect (S.E) The shielding effect is when the outermost electrons, the valence electrons, are shielded from the nucleus by the core electrons. They experience low attraction force when more energy shells are being added and they experience high attraction force when there aren’t much energy shells.  Shielding Effect Trend Shielding effect increases down a group since more energy shells are being added. Shielding effect stays the same across a period, because the number of energy shells remains the same, no energy shells are being removed or added. Trends across a period and down a group A.R ↓ Zeff ↑ S.E → A.R ↑ Zeff → S.E ↑ Investigation 2- Experience 3 Periodic Trends (Pt. 2)  Cations and Anions Cations and Anions are ions, and ions form when an atom gains or loses an electron or more. Cations lose electrons and form positive ions. Anions gain electrons form negative ions.  Cations vs. Parent/Neutral Atom Cations tend to lose electrons. For example, sodium (Na), has 11 electrons, and 1 valence electron. So, it will lose that one valence electron to form an octet, which is 8 valence electrons. Cations are smaller than their neutral atoms since they lose an electron or more. Cation < Neutral Atom Na > Na+  Anions vs. Parent/Neutral Atom Anions tend to gain electrons. For example, oxygen (O), has 8 electrons, and 6 valence electron. So, it will gain 2 electrons to form an octet, which is 8 valence electrons. Anions are bigger than their neutral atoms since they gain an electron or more. Anion > Neutral Atom O < O-2  Cation Anion Metals Non-metals Loses electron (1, 2, 3) Gains electrons (5, 6, 7) +ions -ions  Ionic Radius (I.R) and it’s Trend Ionic radius is the measure of the size of an ion that has gained or lost an electron or more. (Cations and Anions). Ionic radius decreases across a period due to increasing Zeff. Ionic radius increases down a group because more energy levels are being added. Trends across a period and down a group A.R ↓ Zeff ↑ S.E → I.R ↓ A.R ↑ Zeff → S.E ↑ I.R ↑  Ionization Energy (I.E) Ionization energy is the energy needed (absorbed) to remove an electron or more. When removing electrons, the target is an octet of 8 valence electrons, so when ionization energy increases stability increases.  Size vs I.E and I.E Trend As size decreases, ionization energy increases. Because it is harder to remove electrons from smaller atoms, so it will require more energy. Which means when A.R decreases, I.E increases, and when A.R increases, I.E decreases. So, across a period I.E increases Down a group I.E decreases Trends across a period and down a group A.R ↓ Zeff ↑ S.E → I.R ↓ I.E ↑ A.R ↑ Zeff → S.E ↑ I.R ↑ I.E ↓ Investigation 2- Experience 3 Periodic Trends (Pt. 3)  Electron Affinity (E.A) Electron affinity is the energy change that happens when an atom gains an electron. For most atoms, energy is released when an electron is added to the atom. An atom with a higher electron affinity will release a greater amount of energy. A higher electron affinity has a more negative electron affinity value.  Electron Affinty Trend Across a period, electron affinity increases. Increasing nuclear charge along the same sublevel attracts electrons more strongly. Down a group, electron affinity decreases. Increasing atomic radius means that mor energy shells are being added, so when the added electron is futher from the nucleus, it experiences less attraction force. As a result, the atom does not release as much energy when gaining an electron, making the electron affinity less negative.  Trends across a period and down a group (→ means stays the same) A.R ↓ Zeff ↑ S.E → I.R ↓ I.E ↑ E.A ↑ A.R ↑ Zeff → S.E ↑ I.R ↑ I.E ↓ E.A ↓  Electronegativity (E.N) Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound. The most electronegative element, fluorine, is arbitrarily assigned an electronegativity of four.  Electronegativity Trend Electronegativity tends to increase across a period and tend to decreases down a group. The attraction between valence electrons and nucleus increases as theatomic radius decreases across a period.  FINAL CONCLUSION (→ means stays the same) A.R ↓ Zeff ↑ S.E → I.R ↓ I.E ↑ E.A ↑ E.N ↑ A.R ↑ Zeff → S.E ↑ I.R ↑ I.E ↓ E.A ↓ E.N ↓