FC #4 E The Periodic Table of Elements and Stoichiometry
Metric Units commonly used in chem context
amu = 1 atomic unit Volume: fluid ounce (oz), cup (c), pint (pt), quart (qt), gallon (gal) 2 c = 1 pt 32 oz = 1 qt 2 pt = 1 qt 4 qt = 1 gal Weight: ounce (oz), pound (lb), ton 16 oz = 1 lb 2000 lb = 1 ton Time: second (s), minute (min), hour (h), day (d), year (y) 60 s = 1 min 24 h = 1 d 60 min = 1 h 3651/4 d = 1 y Prefix Symbol Meaning femto- f x 1/1,000,000,000,000,000 (10-15) pico- p x 1/1,000,000,000,000 (10-12) nano- n x 1/1,000,000,000 (10-9) micro- � x 1/1,000,000 (10-6) milli- m x 1/1,000 (10-3) centi- c x 1/100 (10-2) deci- d x l/10(10-1) kilo- k x 1,000 (103) mega- M x 1,000,000 (106) giga- G x 1,000,000,000 (109) tera- T x 1,000,000,000,000 (1012)
Empirical vs. Molecular Formula
Similarly, the formula weight of an ionic compound is found by adding up the atomic weights of the constituent ions according to its empirical formula, and its units are also amu per molecule The molecular formula is either the same as the empirical formula or a multiple of it. To calculate the molecular formula, you need to know the mole ratio (this will give you the empirical formula) and the molar mass (molar mass divided by empirical formula weight will give the multiplier for the empirical formula-to-molecular formula conversion).
Electron shells and the size of atoms
Think of an atom as a cloud of electrons surrounding a dense core of protons and neutrons. The atomic radius of an element is thus equal to one-half of the distance between the centers of two atoms of an element that are briefly in contact with each other. The distance between two centers of circles in contact is akin to a diameter, making this radius calculation simple. The atomic radius cannot be measured by examining a single atom because the electrons are constantly moving around, making it impossible to mark the outer boundary of the electron cloud.
Transition metals
Transition metals are Group B elements - they have two or more oxidation states. Their valence electrons are loosely held to their atoms, they're free to move - so they're good conductors of heat and electricity. Valence electrons are found in the d subshell usually. - Can be non-reactive, like copper, nickel, silver, gold, palladium and platinum - making them ideal for jewelry/coins.
Mole concept, Avogadro's number NA
A mole is a quantity of any substance (atoms, molecules, dollar bills, kittens—anything) equal to the number of particles that are found in 12 grams of carbon-12 (612C). This number of particles is defined as Avogadro's number (NA), 6.022 × 1023 mol-1. One mole of a compound has a mass in grams equal to the molecular or formula weight of the compound in amu. For example, one molecule of H2CO3 (carbonic acid) has a mass of 62 amu; one mole of the compound has a mass of 62 grams. The mass of one mole of a compound is called its molar mass and is usually expressed in The term molecular weight is sometimes used incorrectly to imply molar mass; remember, molecular weight is measured in amu/molecule, not g/mol
Representative elements
Also known as the A elements. Include groups Ia through VIIA. The elements in these groups have their valence electrons in the orbitals of either s or p shells. Non-representative Elements = B elements - they include transition elements.
Valence electrons
As the positivity of the nucleus increases, the electrons surrounding the nucleus, including those in the valence shell, experience a stronger electrostatic pull toward the center of the atom. This causes the electron cloud, which is the outer boundary defined by the valence shell electrons, to move closer and bind more tightly to the nucleus. This electrostatic attraction between the valence shell electrons and the nucleus is known as the effective nuclear charge (Zeff), a measure of the net positive charge experienced by the outermost electrons. This pull is somewhat mitigated by nonvalence electrons that reside closer to the nucleus. For elements in the same period, Zeff increases from left to right
Balancing equations, including redox reactions
Because chemical equations express how much and what types of reactants must be used to obtain a given quantity of product, it is of utmost importance that the reaction be balanced so as to reflect the laws of conservation of mass and charge. The mass of the reactants consumed must equal the mass of products generated. More specifically, one must ensure that the number of atoms of each element on the reactant side equals the number of atoms of that element on the product side. Stoichiometric coefficients, which are the numbers placed in front of each compound, are used to indicate the relative number of moles of a given species involved in the reaction. For example, the balanced equation expressing the combustion of nonane is: C9H20 (g) + 14 O2 (g) → 9 CO2 (g) + 10 H2O (l) The coefficients indicate that one mole of C9H20 gas must be reacted with fourteen moles of O2 gas to produce nine moles of carbon dioxide and ten moles of water. In general, stoichiometric coefficients are given as whole numbers.
Metals and non-metals
Metals are found on the left side and in the middle of the Table, while non metals are found predominantly on the upper right side of the table. Metals are malleabile and are able to be pulled/drawn into wires (Ductile). They have low effective nuclear charge and low electronegativity. They have large atomic radii and small ionic radii and they have a low ionization energy. Easily give up electrons. Non metals are brittle in solid state, and show little to no metallic luster. - High ionization energies, electron affinities, and electronegativities as well as small atomic radii and large ionic radii. They are poor conductors. - Unable to give up electrons easily - and less unified in their chemical/physical properties than the metals. - Carbon = non metal that retains solid structure but is brittle etc.
Molecular Weight
Molecular weight, then, is simply the sum of the atomic weights of all the atoms in a molecule, and its units are atomic mass units (amu) per molecule.
First and second ionization energy (Definition and Prediction from electronic structure for elements in different groups or rows)
The energy necessary to remove the first electron is called the first ionization energy; the energy necessary to remove the second electron from the univalent cation (X+) to form the divalent cation (X2+) is called the second ionization energy, and so on. Elements in Groups IA and IIA (Groups 1 and 2), such as lithium and beryllium, have such low ionization energies that they are called the active metals. The active metals do not exist naturally in their neutral forms; they are always found in ionic compounds, minerals, or ores. The loss of one electron from the alkali metals (GroupIA) or the loss of two electrons from the alkaline earth metals (Group IIA) results in the formation of a stable, filled valence shell. In contrast, the Group VIIA (Group 17) elements—the halogens—do not typically give up their electrons. In fact, in their ionic form, they are generally anions. The values for second ionization energies are disproportionally larger for Group IA monovalent cations (like Na+) but generally not that much larger for Group IIA or subsequent monovalent cations (like Mg+). This is because removing one electron from a Group IA metal results in a noble gas-like electron configuration. Group VIIIA (Group 18) elements, or noble or inert gases, are the least likely to give up electrons. They already have a stable electron configuration and are unwilling to disrupt that stability by giving up an electron. Therefore, noble gases are among the elements with the highest ionization energies.
Theoretical Yields
The yield of a reaction can refer to either the amount of product predicted (theoretical yield) or actually obtained (raw or actual yield) when a reaction is carried out. Theoretical yield is the maximum amount of product that can be generated as predicted from the balanced equation, assuming that all of the limiting reactant is consumed, no side reactions have occurred, and the entire product has been collected. Theoretical yield is rarely ever attained through the actual chemical reaction. Actual yield is the amount of product one actually obtains during the reaction. The ratio of the actual yield to the theoretical yield, multiplied by 100 percent, gives the percent yield.
Noble gases: their physical and chemical characteristics
The noble gases (historically also the inert gases) make a group of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). Oganesson (Og) is predicted to be a noble gas as well, but its chemistry has not yet been investigated. For the first six periods of the periodic table, the noble gases are exactly the members of group 18 of the periodic table. Noble gases are typically highly unreactive except when under particular extreme conditions. The inertness of noble gases makes them very suitable in applications where reactions are not wanted. The noble gases have weak interatomic force, and consequently have very low melting and boiling points. They are all monatomic gases under standard conditions, including the elements with larger atomic masses than many normally solid elements.[9] Helium has several unique qualities when compared with other elements: its boiling and melting points are lower than those of any other known substance; it is the only element known to exhibit superfluidity; it is the only element that cannot be solidified by cooling under standard conditions—a pressure of 25 standard atmospheres (2,500 kPa; 370 psi) must be applied at a temperature of 0.95 K (−272.200 °C; −457.960 °F) to convert it to a solid.[24] The noble gases up to xenon have multiple stable isotopes. Radon has no stable isotopes; its longest-lived isotope. The noble gas atoms, like atoms in most groups, increase steadily in atomic radius from one period to the next due to the increasing number of electrons. Chemical: The noble gases have full valence electron shells. Valence electrons are the outermost electrons of an atom and are normally the only electrons that participate in chemical bonding. Atoms with full valence electron shells are extremely stable and therefore do not tend to form chemical bonds and have little tendency to gain or lose electrons.[27] However, heavier noble gases such as radon are held less firmly together by electromagnetic force than lighter noble gases such as helium, making it easier to remove outer electrons from heavy noble gases. As a result of a full shell, the noble gases can be used in conjunction with the electron configuration notation to form the noble gas notation. To do this, the nearest noble gas that precedes the element in question is written first, and then the electron configuration is continued from that point forward. For example, the electron notation of phosphorus is 1s2 2s2 2p6 3s2 3p3, while the noble gas notation is [Ne] 3s2 3p3. This more compact notation makes it easier to identify elements, and is shorter than writing out the full notation of atomic orbitals. The noble gases show extremely low chemical reactivity; consequently, only a few hundred noble gas compounds have been formed. Neutral compounds in which helium and neon are involved in chemical bonds have not been formed (although there is some theoretical evidence for a few helium compounds), while xenon, krypton, and argon have shown only minor reactivity.[29] The reactivity follows the order Ne < He < Ar < Kr < Xe < Rn.
Electron affinity (Definition & Variation with group and row)
"Electron affinity refers to the energy dissipated by a gaseous species when it gains an electron. Note the electron affinity is essentially the opposite concept from ionization energy. Because this is an exothermic process, ΔHrxn has a negative sign; however, the electron affinity is reported as a positive number. This is because electron affinity refers to the energy dissipated: if of energy is released, and the electron affinity is The stronger the electrostatic pull (the higher the Zeff) between the nucleus and the valence shell electrons, the greater the energy release will be when the atom gains the electron. Thus, electron affinity increases across a period from left to right. Because the valence shell is farther away from the nucleus as the principal quantum number increases, electron affinity decreases in a group from top to bottom. Groups IA and IIA (Groups 1 and 2) have very low electron affinities, preferring to give up electrons to achieve the octet configuration of the noble gas in the previous period. Conversely, Group VIIA (Group 17) elements have very high electron affinities because they need to gain only one electron to achieve the octet configuration of the noble gases (Group VIIIA or Group 18) in the same period. Although the noble gases would be predicted to have the highest electron affinities according to the trend, they actually have electron affinities on the order of zero because they already possess a stable octet and cannot readily accept an electron. Most metals also have low electron affinity values.
Electronegativity (definition & comparative values for some representative elements and important groups).
"Electronegativity is a measure of the attractive force that an atom will exert on an electron in a chemical bond. The greater the electronegativity of an atom, the more it attracts electrons within a bond. Electronegativity values are related to ionization energies: the lower the ionization energy, the lower the electronegativity; the higher the ionization energy, the higher the electronegativity. The first three noble gases are exceptions: despite their high ionization energies, these elements have negligible electro-negativity because they do not often form bonds. The electronegativity value is a relative measure, and there are different scales used to express it. The most common scale is the Pauling electronegativity scale, which ranges from 0.7 for cesium, the least electronegative (most electropositive) element, to 4.0 for fluorine, the most electronegative element. Electronegativity increases across a period from left to right and decreases in a group from top to bottom. Figure 2.9 shows the electronegativity values of the elements.
Electron shells and the size of Ions
"Unlike atomic radii, ionic radii will require some critical thinking and Periodic Table geography to determine. In order to understand ionic radii, we must make two generalizations. One is that metals lose electrons and become positive, while nonmetals gain electrons and become negative. The other is that metalloids can go in either direction, but tend to follow the trend based on which side of the metalloid line they fall on. Thus, silicon (Si) behaves more like a nonmetal, while germanium (Ge) tends to act like a metal. On the MCAT, these generalizations can also be inferred from information found in passages and questions, such as oxidation states in compounds.
Description of reactions by chemical equations
COMBINATION: A combination reaction has two or more reactants forming one product. The formation of water by burning hydrogen gas in air is an example of a combination reaction. DECOMPOSITION: A decomposition reaction is the opposite of a combination reaction: a single reactant breaks down into two or more products, usually as a result of heating, high-frequency radiation, or electrolysis. An example of decomposition is the breakdown of mercury(II) oxide. (The Δ [delta] sign over a reaction arrow represents the addition of heat.) An example of a reaction which utilizes high-frequency light is the decomposition of silver chloride in the presence of sunlight, shown in Figure 4.3. The ultraviolet component of sunlight has sufficient energy to catalyze certain chemical reactions. COMBUSTION: A combustion reaction is a special type of reaction that involves a fuel—usually a hydrocarbon—and an oxidant (normally oxygen). In its most common form, these reactants form the two products of carbon dioxide and water. SINGLE DISPLACEMENT: A single-displacement reaction occurs when an atom or ion in a compound is replaced by an atom or ion of another element. For example, solid copper metal will displace silver ions in a clear solution of silver nitrate to form a blue copper sulfate solution and solid silver metal. DOUBLE DISPLACEMENT: In double-displacement reactions, also called metathesis reactions, elements from two different compounds swap places with each other to form two new compounds. This type of reaction occurs when one of the products is removed from the solution as a precipitate or gas or when two of the original species combine to form a weak electrolyte that remains undissociated in solution. For example, when solutions of calcium chloride and silver nitrate are combined, insoluble silver chloride forms in a solution of calcium nitrate. NEUTRALIZATION REACTIONS: "Neutralization reactions are a specific type of double-displacement reaction in which an acid reacts with a base to produce a salt (and, usually, water). For example, hydrochloric acid and sodium hydroxide will react to form sodium chloride and water: HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
Limiting Reactants
Rarely are reactants added in the exact stoichiometric proportions shown in the balanced equation of a reaction. As a result, in most reactions, one reactant will be used up or consumed first. This reactant is known as the limiting reagent (or reactant) because it limits the amount of product that can be formed in the reaction. The reactants that remain after all the limiting reagent is used up are called excess reagents (or reactants) For problems involving the determination of the limiting reagent, keep in mind two principles: All comparisons of reactants must be done in units of moles. Gram-to-gram comparisons will be useless and may even be misleading. It is not the absolute mole quantities of the reactants that determine which reactant is the limiting reagent. Rather, the rate at which the reactants are consumed (the stoichiometric ratios of the reactants), combined with the absolute mole quantities determines which reactant is the limiting reagent.
Alkali metals
The alkali metals are a group (column) in the periodic table consisting of the chemical elements lithium (Li), sodium (Na), potassium (K),[note 1] rubidium (Rb), caesium (Cs),[note 2] and francium (Fr). This group lies in the s-block of the periodic table of elements as all alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in them having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. The alkali metals are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to oxidation by atmospheric moisture and oxygen (and in the case of lithium, nitrogen). Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in salts and never as the free elements. Caesium, the fifth alkali metal, is the most reactive of all the metals. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements,[note 3] excluding hydrogen (H), which is nominally a group 1 element but not normally considered to be an alkali metal as it rarely exhibits behaviour comparable to that of the alkali metals. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones. All of the discovered alkali metals occur in nature as their compounds: in order of abundance, sodium is the most abundant, followed by potassium, lithium, rubidium, caesium, and finally francium, which is very rare due to its extremely high radioactivity; francium occurs only in the minutest traces in nature as an intermediate step in some obscure side branches of the natural decay chains.
Alkaline earth metals: their chemical characteristics
The alkaline earth metals are six chemical elements in column (group) 2 of the Periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).[1] The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.[2] Structurally, they have in common an outer s- electron shell which is full;[2][3][4] that is, this orbital contains its full complement of two electrons, which these elements readily lose to form cations with charge +2, and an oxidation state (oxidation number) of +2.[5] All the discovered alkaline earth metals occur in nature.[6] Experiments have been conducted to attempt the synthesis of element 120, the next potential member of the group, but they have all met with failure.
Halogens: their chemical characteristics
The halogens or halogen elements (/ˈhælədʒən, ˈheɪ-, -loʊ-, -ˌdʒɛn/[1][2][3]) are a group in the periodic table consisting of five chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The artificially created element 117 (tennessine, Ts) may also be a halogen. In the modern IUPAC nomenclature, this group is known as group 17. The symbol X is often used generically to refer to any halogen. The name 'halogen' means 'salt-producing'. When halogens react with metals they produce a wide range of salts, including calcium fluoride, sodium chloride (common table salt), silver bromide and potassium iodide. The group of halogens is the only periodic table group that contains elements in three of the four main states of matter at standard temperature and pressure. All of the halogens form acids when bonded to hydrogen. Most halogens are typically produced from minerals or salts. The middle halogens, that is chlorine, bromine and iodine, are often used as disinfectants. Organobromides are the most important class of flame retardants. Elemental halogens are dangerously to potentially lethally toxic. The halogens show trends in chemical bond energy moving from top to bottom of the periodic table column with fluorine deviating slightly. (It follows trend in having the highest bond energy in compounds with other atoms, but it has very weak bonds within the diatomic F2 molecule.) This means, as you go down the periodic table, the reactivity of the element will decrease because of the increasing size of the atoms.[7] Halogen bond energies (kJ/mol) X X2 HX BX3 AlX3 CX4 F 159 574 645 582 456 Cl 243 428 444 427 327 Br 193 363 368 360 272 I 151 294 272 285 239 Halogens are highly reactive, and as such can be harmful or lethal to biological organisms in sufficient quantities. This high reactivity is due to the high electronegativity of the atoms due to their high effective nuclear charge. Because the halogens have seven valence electrons in their outermost energy level, they can gain an electron by reacting with atoms of other elements to satisfy the octet rule. Fluorine is one of the most reactive elements, attacking otherwise-inert materials such as glass, and forming compounds with the usually inert noble gases. It is a corrosive and highly toxic gas. The reactivity of fluorine is such that, if used or stored in laboratory glassware, it can react with glass in the presence of small amounts of water to form silicon tetrafluoride (SiF4).
Oxygen group
The oxygen family, also called the chalcogens, consists of the elements found in Group 16 of the periodic table and is considered among the main group elements. It consists of the elements oxygen, sulfur, selenium, tellurium and polonium. These can be found in nature in both free and combined states. The group 16 elements are intimately related to life. We need oxygen all the time throughout our lives. Oxygen: 1s2 2s2 2p4 Sulfur: 1s2 2s2p6 3s2p4 Selenium: 1s2 2s2p6 3s2p6d10 4s2p4 Tellurium: 1s2 2s2p6 3s2p6d10 4s2p6d10 5s2p4 Polonium: 1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p4
Description of composition by percent mass
The percent composition of an element (by mass) is the percent of a specific compound that is made up of a given element. To determine the percent composition of an element in a compound, the following formula is used: One can calculate the percent composition of an element by using either the empirical or the molecular formula. It is also possible to determine the molecular formula given both the percent compositions and molar mass of a compound.
Definition of Density
ratio between mass and volume or mass per unit volume. Measure how much is in a unit volume It's a physical property of matter. Measure of heaviness. mass/vol = g/mL
Metalloids
separate metals and non-metals on the PT. Called semimetals - share some characteristics of both. Halfway point for pretty much everything and vary widely on chemical and physical characteristics. Ex: Si, B, na, F, Ge, As, Sb, Te, Po, At etc
