2ElementsAll words in the English language are the result of the 26 letters of the alphabet.All substances on our planet and the universe are the result of about 88 known “building blocks” called the elements.Why 88?
3Elements An element cannot be decomposed into a simpler substance. The smallest particle of an element is the atom.Atoms are incredibly small.
4ElementsEvery element has a one or two letter designation called its _____________.In writing a symbol, the first letter is capitalized and the second letter is lowercase.C = carbonCo = cobaltBut, CO = a compound of carbon and oxygen!
5Distribution of the Elements Most elements are solids at 25oC.Br and Hg are liquidsH, N, O, F, Cl, He, Ne, Ar, Kr, Xe, and Ra are gasesSilicon and oxygen make up almost 75% of the Earth’s crust.
7History of the Elements Some elements were known to ancient man like Copper and Gold.Names and symbols are based in Latin languageCopper = Cuprum; symbol CuGold = Aurum; symbol Au
8Common Elements Aluminum Argon Arsenic Barium Boron Bromine Calcium CarbonChlorineChromiumCobaltCopperFluorineHeliumHydrogenIodineIronLeadLithiumMagnesiumManganeseMercuryNeonNickelNitrogenOxygenPhosphorusPotassiumSiliconSilverSodiumStrontiumSulfurTinTitaniumVanadiumZinc
9Periodic Table Dimitri Mendeleev, 1869 Elements are arranged into vertical columns called groups.Elements within the same group tend to react in the same way.Horizontal row = period.
10Periodic Table Main (representative) groups = A Transition groups = B Groups with special namesAlkali metal, alkaline earth metal, halogens, and the noble gases.Actinide and lathanides.
11Periodic TableA stair-step line on the right-hand side of the chart separates the metals from the non-metals.Metals are solids, have luster (shine), are good conductors, are malleable,and are ductile. Most have a high density and high melting point.
12Periodic TableNon-metals are dull, are poor conductors, and have low melting points and densities.Metalloids are elements that fall on or near the line and have properties of both metals and non-metals.B, Si, Ge, As, Sb, Te, and PoHydrogen – a special exception.
14Learning CheckDescribe each in terms of a Group, Period, and Metal, non-metal, or metalloid.ElementGroupPeriodM/NMMgCFeAs
15Elements in NatureElements are rarely found in their pure form in nature.Exceptions are metals like Gold, Silver, and Platinum; non-metals like Nitrogen and Oxygen; and the noble gases.Most are combined with other elements as compounds.
16Diatomics Some important elements occur as two atoms bonded together. The list is:
17Compounds Compounds are classified as either Molecular or Ionic. Molecular (aka covalent) compounds are formed between two or more non-metals who share electrons.Ionic compounds are formed between a cation (+) and an anion (-).
18Compounds Metals lose electrons and form cations. Na Na+1 + 1e-Non-metals gain electrons and form anions.Cl + 1e- Cl-1Thus, an ionic compound will have a metal and a non-metal in its formula.
19CompoundsLaw of Constant Composition – any sample of a compound will always have the same ratio or mass percentage of its elements.Water always has two hydrogen atoms and one oxygen atom per formula.Sodium chloride always has one sodium and one chlorine atom per formula.
20Chemical Formulas Are a shorthand method for writing names. Subscripts indicate the number of each of the elements in the compound.A subscript of one is NEVER written.Ex) CO2, MgBr2, C6H12O6.
21Learning CheckDecide whether the following would be a molecular or ionic compound.CompoundTypeMgBr2SO2FeCl3PF3
22Chapter 5 Atomic Theory Discovery of Atomic Structure Subatomic ParticlesNuclear Atom
23Dalton’s Model All matter is made up of tiny particles called atoms. All atoms of a given element are similar to one another; atoms of different elements are different from each other.Atoms of two or more different elements combine to form compounds.A chemical reaction involves the rearrangement of atoms into new combinations. Atoms are never created nor destroyed in a chemical reaction.
24Parts of an AtomExperiments performed around the turn of the previous century (~1900), showed that atoms were made of several types of particles – collectively referred to as subatomic particles.These experiments showed that three types of particles were present in an atom.
25Subatomic ParticlesA proton has a +1 charge and an approximate mass of 1 amu.Note: an atomic mass unit (amu) is equal to 1/12 of the mass of a Carbon atom with 6 protons and 6 neutrons.A neutron has no charge, but does have a mass of about 1 amu.An electron has a –1 charge and a mass so small that we usually say that it weighs 0 amu.
26Atomic StructureErnest Rutherford performed an experiment called the “Gold Foil” experiment in 1911.He used an alpha particle (2P + 2N) source and fired them at a piece of very thin gold foil.He expected all of the particles to pass straight through. However, some were deflected and some were even reflected backwards.In Rutherford’s words, it was as if he had shot a cannonball at a piece of tissue paper and have it bounce backwards.
28Results Only 1 in 8000 alpha particles is scattered. Scattering occurs when an alpha particle encounters a gold nuclei.A nucleus is very small and contains both the protons and the neutrons. Thus, it contains almost all of the mass of an atom.This very dense center is surrounded by the electron cloud, which is occupied by the fast moving electrons.Thus, an atom is MAINLY EMPTY SPACE.
30Atomic Number & Mass Number All atoms of the same element have the same number of protons.This distinguishes one element from another.The number of protons is also called the atomic number.This is always the integer found on the periodic chart with each chemical symbol.
31Atomic Number & Mass Number Atoms are electrically neutral. Thus, each element must have an equal number of protons and electrons.The mass number of an atom is equal to the sum total of the protons and neutrons in the nucleus.Mass number and atomic weight (found on the periodic chart) are NOT the same thing.
33Isotopes All atoms of one element have the same number of protons. But, they can have different numbers of neutrons, and hence, a different mass number.These different versions of atoms from one element are called isotopes.
34IsotopesUse the chemical symbol, atomic number (Z), and mass number (A) as seen below.Can also list symbol followed by mass number.
35Atomic MassThe masses found for each element on the periodic chart are the weighted average of all the known isotopes for that element.Example: Chlorine has only two known isotopes – Cl-35 and Cl-37. Cl-35 is found 75.5% of the time and Cl-37 is found 24.5% of the time.
36Isotope Mass X Percent = Contribution (approximate) to total mass35 amu X = amu37 amu X = amuTotals amuWith all elements, round A.W.’s to one decimal place.
37Study CheckWhat is the Atomic Weight of each element rounded to 0.1amu?NaSiClK