3ElementsA pure substance that cannot be broken down into simpler substances by a chemical reactionIdentified by a one- or two-letter symbolArranged in the periodic tableIts location on the periodic table indicates a lot about its chemical propertiesCan be a metal, nonmetal, or a metalloid
4Elements Some of the element symbols will be familiar to you already It will take time and practice to learn others
7ElementsMetals- located to the left of the stair step line (top located near Boron)ShinyGood conductors of heat and electricitySolid at room temperature except for mercury
8ElementsNonmetals – except for hydrogen (H) these are located to the right of the stair step line (top located near Boron)Do not have a shiny appearanceGenerally poor conductors of heat and electricityUsually a solid or gas at room temperature (exception: Br2 is a liquid at room temperature)
9ElementsMetalloids – 7 elements located along the stair step line (top located near Boron)Properties in between metals and nonmetalsMetallic shine but brittleBoron (B)Silicon (Si)Germanium (Ge)Arsenic (As)Antimony (Sb)Tellurium (Te)astatine (At)
11CompoundsA pure substance formed by chemically combining two or more elementsA chemical formula for a compound consists of:Element symbols to show the identity of the elements that form a compoundSubscripts to show the ratio of atoms in the compoundH2OH2OC3H8C3H82 H atoms1 O atom3 C atoms8 H atoms
12CompoundsCan be drawn many ways but we are always making a simplified representation of reality
134 Common ways to draw compounds H HLineLewis Dot Diagram
14Atoms All mater is composed of building blocks called atoms Atoms are composed of three subatomic particlesProtonNeutronElectron
15AtomsThe mass of an atom is very small since each proton and neutron has a mass of XChemists use the atomic mass unit (amu) to measure the mass of an element
16Subatomic ParticlesThe nucleus is the dense core that contains the protons and neutronsMost of the mass of an atom is in the nucleusElectron cloud is composed of electrons that are in almost empty space around nucleus
17Subatomic Particles Opposite charges attract each other Like charges repel each otherProtons and electrons attract each other but electrons repel each other
18Atomic NumberThe number of protons in the nucleus of an atom is its atomic numberEvery atom of a given element has the same number of protons in the nucleusWe can symbolize the number of protons with the generic letter ZA neutral atom has no overall chare so:Z= number of protons = electronsExample: LithiumAtomic number (Z) isthe number of protonsin the nucleus.3Li
19IsotopesAtoms of the same element that have a different number of neutronsThe number of protons remains constantDifferent forms of the same elementThe mass number (A) represents the number of protons plus the number of neutronsA = Z + number of neutronsExample – two forms of carbon:C-12 has 6 neutronsC-14 has 8 neutronsZ = 6 for both forms of carbon
20Example Cl Mass number (A) Atomic number (Z) # of protons = 17 35ClAtomic number (Z)17# of protons = 17# of electrons = 17# of neutrons = A – Z = 35 – 17 = 18
21Atomic WeightThe weighted average of the masses of the naturally occurring isotopes of a particular element reported in atomic mass units (amu)This information can be found on the periodic table6C12.01atomic number (Z)element symbolatomic weight (amu)
22Atomic Weight Calculation 1 The weighted average of the ass of the naturally occurring isotopesExampleWhat is the atomic weight of chlorine?List each isotope, it’s mass in atomicmass units, and it’s abundance in nature.Step IsotopeMass (amu)Isotopic AbundanceCl-3534.9775.78% =Cl-3736.9724.22% =
23Atomic Weight Calculation 2 Multiply the isotopic abundance by the massof each isotope, and add up the products.Step The sum is the atomic weight of the element.x=amux=amu35.45 amuamu=4 sig. figs.Answer4 sig. figs.
24Organizing the elements Periodic table was put together over time as the elements were discovered, isolated, and studied.Many versions exist but the most common is based on the one developed by Dmitri Mendeleev in 1869A row in the periodic table is called a periodElements in the same row are similar in sizeA column in the periodic table is called a groupElements in the same group have similar electronic and chemical properties
26Periodic Table - Groups Alkali MetalsAlkaline Earth MetalsTransition MetalsLanthanide & ActinideHalogensNobel GasesVery reactiveMetals except for H+1 ionsReact with Oxygen to form compounds that dissolve into alkaline solutions in waterReactive+2 ionsOxygen compounds are strongly alkalineMany are not water solubleMetalsForm ions with several different charges (oxidation states)Tend to form +2 and +3 ionsLanthanides 58 – 71Actinides90 – 103Actinides are radioactiveForm diatomic molecules in elemental state-1 ionsSalts with alkali metalsInertHeavier elements have limited reactivityDo not form ionsMonoatomic gases
27Carbon is SpecialCarbon’s ability to join with itself and other elements gives it a versatility not seen with any other element in the periodic tableElemental forms of carbon include the following carbon-only structures:diamondgraphitebuckminsterfullerene
28Carbon“the party animal of the atomic world, latching onto many other atoms (including itself) and holding tight, forming molecular conga lines of hearty robustness-the very trick of nature necessary to build proteins and DNA”Bill Bryson from A Short History of Nearly Everything
29Electronic StructureThe chemical properties of an element are determined by the number of electrons in an atomElectrons do not move freely in space – restricted to a region with a particular energyElectrons occupy discrete energy levels that are restricted to specific values – the energy is “quantized”Electrons are confined to regions called the principal energy levels or shells
30Electron ShellsThe shells are numbers, n=1, 2, 3, 4… Moving out from the nucleusElectrons closer to the nucleus are held more tightly are lower in energyElectrons farther from the nucleus are held less tightly and are higher in energyThe farther a shell is from the nucleus, the larger its volume, and the more electrons it can hold
34OrbitalsThe maximum number of electrons that can occupy a shell is determined by the number of orbitals in a shell
35Electron Configuration The electron configuration shows how the electrons are arranged in an atom’s orbitalsThe ground state is the lowest energy arrangementThe outtermost shell is the valance shellThe electrons in the valence shell are called valence electronsThe chemical properties of an element depend on the number of electrons in the valence shell
36Electron Configuration Rule 1:Electrons are placed in the lowest energy orbital beginning with the 1s orbital.Orbitals are then filled in order of increasing energy.Rule 2:Each orbital holds a maximum of 2 electronsRule 3:1 electron is added to each orbital until all of orbitals are half-filledThen, the orbitals can be completely filled
38Example What would the electron configuration for fluorine (F) be? Atomic Number = 9 so it has nine electronsShells fill: 1s22s22p5How many valence electrons does it have?There are 7 electrons in the 2nd shell so there are 7 valence electrons
39Examples Be Cl 1s22s2 1s22s22p63s23p5 valence shell: n = 2 Atomic number: 4Atomic number: 171s22s21s22s22p63s23p5valence shell: n = 2valence shell: n = 3# ofvalence electrons = 2# ofvalence electrons = 7
40Valence ElectronsElements in the same group have similar electron configurations.Elements in the same group have the same number of valence electrons.The group number, 1A–8A, equals the number of valence electrons for the main group elements.The exception is He, which has only 2 valence electrons.The chemical properties of a group are therefore very similar.
42Electron Dot SymbolsDots representing valence electrons are placed on the four sides of an element symbolEach dot represents one valence electronFor 1 to 4 valence electrons, single dots are usedWith more than 4 valence electrons the dots are pairedElement:# of Valence electrons:Electron-dot symbol:H1C4O6Cl7
43Periodic Trends The size of atoms increases down a column, as the valence e− arefarther from thenucleus.IncreasesDecreasesThe size of atoms decreases across a row, as the number of protons in the nucleus increases, pulling the valence electrons in closer.
44Periodic Trends The ionization energy is the energy needed to remove DecreasesThe ionization energy is the energy needed to removean electron from a neutral atom.Na energy Na e–Ionization energiesdecrease down acolumn as thevalence e− getfarther away fromthe positively charged nucleus.IncreasesIonization energies increase across a row as thenumber of protons in the nucleus increases.