Chapter 4 and 5
Chapter 4 and 5 Chemistry 111
C of C
Popular in Chemistry 111
Popular in Chemistry
This 7 page Class Notes was uploaded by Kayla Reece on Tuesday April 26, 2016. The Class Notes belongs to Chemistry 111 at College of Charleston taught by Dr. Forconi in Spring 2016. Since its upload, it has received 9 views. For similar materials see Chemistry 111 in Chemistry at College of Charleston.
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Date Created: 04/26/16
v in 1864, John Newlands noted that when the elements were arranged in order of atomic th number that every 8 element has similar properties Ø he referred to this as the law of octaves v in 1869 Dmith Mehdeler and Lother Meyer independently proposed the idea of periodicity Ø Mehdeller group the elements according to properties § Predicted that properites of elements that were not yet discovered § Could not explain in consistence’s in the table v In 1913, Henry Moseley discovered the correlation between the # of protons (atomic#) and frequency x-rays generated Ø Ordering the periodic table by atomic # and symbol and electron configuration v The main group of elements are 1A-7A v The noble gases are ground in Group 8A and have filled shells v The transition metals are found in Group 1b and 3b-8b Ø Group 2b has filled d subshells and not transition v The lanthanides and actinides make up f block transition elements v There is a distinct pattern to the electron configuration of the elements in a particular group Ø 1A- [Noble Gas] Xs or 2A- [Noble Gas] Xs 2 v the outermost electrons of an atom are called valence electrons Ø included information of covalent bonds Ø help predict chemical properties v effective nuclear charge (Z ) effthe actual magnitude of the charge that is “experienced” by an electron in an atom Ø in multi0electron atom, electrons are simultaneously attracted to the nucleus and repel each other Ø gets lower and lower has go farther away from the nucleus Ø this results in shielding, where an electron is particularity shielded from the + charge of nucleus by other electrons Ø although electrons shield one another to some extent the most effective are the core electrons Ø as a result, the value of Z effs up steadily from left to right because the core electrons remain the same but Z goes up v In general the Z ieffiven by – Z = eff σ Ø Z is the nuclear charge or simply # of protons Ø σ is the skidding constant- different for different atoms Ø v Several chemical and physical properties of elements depend on Z eff Ø It is useful to visualize the electrons of an atom in the shells Ø If n higher, the distance from nucleus goes up v Atomic radius is the distance between the nucleus of an atom and its valence shell. But in quantum mechanics there is no such thing Ø Atomic radius in metals (metallic radius) is ½ the distance between the nuclei of 2 adjacent , identified metal atoms Ø Atomic radius in nonmetals or covalent radius is half the distance between adjacent identical nuclei connected by bonds v The atomic radius higher from top to bottom down by group Ø Increasing n, so outmost shell lies farther from nucleus v The atomic radius decrease from left to right by periods Ø Higher Z which draws the valence shell close to the nucleus eff Ø Ø increase protons, increase attraction, increase Z so eff electrons pull more towards nucleus decreasing the distance v atomic radius decrease from left to right across a period due to increased electron attraction between effective nuclear charge and the charge of valence shell v ionization energy (IE) is the minimum energy required to remove an electron from an atom in the gas phase Ø the result is anion, a chemical species w/ a net charge v in general, as Z increases, IE increase- IE increases left to right eff v within a given shell electron w/ a higher value as l are increase in energy, thus easier to remove Ø removing a paired electron is easier because the repulse forces between 2 electrons in the same orbital v it is possible to remove additional electrons in subsequent ionization giving IE, IE ,…. 2 v It takes more energy to remove the 2 , 3 4 etc… electrons cause it is harden to remove an electron from a cation than an atom Ø It takes more energy to remove core electrons than valence Ø Core electrons are close to nucleus- experiment greater Z becauseffewer filled shells shielding them from nucleus v Electron affinity (EA) is the energy released when an atom in the gas phase accepts an electron Ø Like IE electron affinity increase from left to right across a period as Z ieffease § Easier to add an electron as the + charge of the nucleus increase Ø With in p shell it is easier to add an electron to an empty orbital Ø More than one electron maybe added to an Ø While many 1 electron affinity are +, subsequent electron affinities are – § Considerable energies required to overcome the repulsive forces between the electron and negative charged ion v Summary of atomic trends Ø v metallic characters-usually from cations Ø metals tend to-shine, malleable (sheets), and ductive Ø be good conductors of both heat and electricity Ø have increase ionization energy commonly from cations v notmetals- usually from anions Ø vary in color and hot shinny Ø be brittle, rather than malleable Ø be poor conductors of both heat and electricity Ø have high EA (commonly from anions) v metalloids are elements w/ properties intermediate between those metals and nonmetals v many period trends of the elements can be explained by using Coulobs Law v Coulomb’s Law- the force between 2 charges (Q +Q ) i1 di2ectly proportional to product of 2 and inversely proportional to the distance between objects Ø F= Q xQ1/d2 or D =d1x s2uare root of Q xQ 1F 2 v To write electron configuration of anion formed by a group of element Ø Write the configuration for the atom Ø add or remove the appropriate # electrons v Ions of elements are formed by removing electrons first form the shell with the high value n v For Fe from Fe , 2 electrons are last from 4s subshell not 3d v The ionic radius is the radius of a cation or an anion Ø When an atom loses an electron to become a cation, its radius decreased due in part to reduction in electron-electron repulsion in the valence shell Ø A significant decrease in radius occurs when all of an atoms valence electrons are removed § More protons= smaller radius v When an atom gains one or more electrons and becomes an anion, its radius increase due to high electron-electron repulsion v An isoelectron senses is a series of 2 or more species that have identical electron configuration, but different effcharges Chapter 5 v A compound is a substance composed of 2 or more elements combined in a specific ration and held together by chemical bonds Ø Water, salt, ammonia, sodium v When atoms form compounds it is their valence electrons that actually interact Ø A lewis dot symbol consists of the element symbol surrounded by dots Ø Each dot represents a valence electron Ø Atoms combine in order to achieve a more stable electron configuration § Max stability results when a chemical species is isoelectric w noble gases Ø Dots are not paired until absolutely necessary Ø For main groups metals such as Na, the # of dots is the # of electrons lost Ø For nonmetals is the second period, the 3 of unpaired dots is the # of bonds an atom can form Ø Ions can also be represented by Lewis dot symbol v Ionic bonding refers to the electrostatic attraction that holds oppositely charged ions together in an ionic compounds v the chemical formula for ionic compounds depicts the constituent elements and the ration which they combine v A 3D array of oppositely charged ions is called Lattice Ø Lattice energy is the amount of energy required to convert a mole of ionic solid to its gas phase v The magnitude of Lattice energy is a measure of an ionic compound stability depends and the magnitude of the charge and distance between v Formulas for ionic compounds are generally empirical formula Ø Ionic compounds are electronically neutral v A monoatomic ion is named by changing the ending of the elements name to end with ide Ø Do not put charge unless can form other charges Ø Smaller charge ends in –ous and large one ends with –ic v In order for ionic compounds to be electronically neutral the sum of the charges on the cation and anion in each formula must be zero Ø If a compound contains a metal and nonmetal it is usually ionic v When compounds form between elements w/ similar properties electrons are not transferred from one electron to another but instead are shared in order to give each atom a noble gas configuration Ø Covalent bonds v A molecule combination of at least 2 atoms in a specific arrangement held together by chemical forces (bonds) v A molecule may be of an element or a compound v Different samples of an atom compound always contain the same elements in the same ratio. This known as the Law of definite proportions v If 2 elements can form 2 or more different compounds, the Law of multiples proportions tell us that the ration of masses of element of one element come w/ masses of the other v Diatomic molecules contain 2 atomic and may be either hetero or homo v A chemical formula denotes the composition of the substance of H2O v A molecular formula shows the exact # of atoms of each element in the molecule v Same elements have 2 or more distinct forms known as allotropes v A structural formula shows not only the elemental comp. but general arrangement v Molecular substances can also be represented using empirical formulas v Remember that binary molecules compounds are substances that consist of just 2 different elements Ø Nomenclature § Name first element that appears into the formula § Write second one that appears change ending –ide v Hydrogen compounds Ø Have different names then most v One definition of an acid is a substance that produces H ions when put in water Ø To name acids-remove gen from hydrogen Ø Change the second element to –ic § A compound must contain one ionizable hydrogen atom to be an acid v Polyatomic ions consist of combination of 2 or more atoms Ø Formulas are determined following the same rules of ionic compounds containing monoatomic ions, ions must combines in a ratio that gives a neutral formula overall v Oxoanions are polyatomic anions that contain 1 or more oxygen’s atoms and one atom of another element v Starting w/ the oxoanions that end in –ate. We can name them as follows Ø The ion w/ one more O atoms than the –ate ion is called per…..ate Ø The ion w/ one less O atom than the –ate is called …..ite ion Ø The ion w/ 2 fewer O atom than the –ate is called the hyper…ite ion v Oxoacids, when dissolved in water, produce H ions and then corresponds oxoanions Ø An acid based on –ate is called –ic acid Ø An acid based on an –ite ion is called –ous acid Ø Prefexies are not in the name of acids v Can have more than one ionizable H atom v A hydrate is a compound that has a specific # water molecules / in its solid structres Ø When water molecule are off by heating the resulting compound is sometimes called anhydrous v The molecular mass is the mass in amu of an individual molecule Ø To calculate molecular mass = #(amu)+#(amu)….. Ø Also called molecular weight v A lost of the % mass of each element in a compounds is known as the % comp. by mass Ø % mass= n x atomic mass/ molecular mass x 100 v we could also have the empirical formula be calculate v the molar mass of a substance is the mass in grams of one mole of the substance Ø the molar mass of an element is = to is atomic mass Ø the molar mass of a compound is the sum of the molar masses of the elements included v using the concept of mole and molar mass we can now use an experimenter determine % comp. to determine the empirical formula and/ or molecular
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