Transcription

THE PERIODIC TABLEDr Marius K [email protected]

COURSE CONTENT1. History of the atom2. Sub-atomic Particles protons, electrons and neutrons3. Atomic number and Mass number4. Isotopes and Ions5. Periodic Table Groups and Periods6. Properties of metals and non-metals7. Metalloids and Alloys

OBJECTIVES Describe an atom in terms of the sub-atomicparticles Identify the location of the sub-atomic particles inan atom Identify and write symbols of elements (atomic andmass number) Explain ions and isotopes Describe the periodic table– Major groups and regions– Identify elements and describe their properties Distinguish between metals, non-metals, metalloidsand alloys

Atom Overview The Greek philosopher Democritus (460B.C. – 370 B.C.) was among the first tosuggest the existence of atoms (from theGreek word “atomos”)– He believed that atoms were indivisible andindestructible– His ideas did agree with later scientifictheory, but did not explain chemicalbehavior, and was not based on thescientific method – but just philosophy

John Dalton(1766-1844)In 1803, he proposed :1. All matter is composed of atoms.2. Atoms cannot be created or destroyed.3. All the atoms of an element are identical.4. The atoms of different elements are different.5. When chemical reactions take place, atoms ofdifferent elements join together to formcompounds.

J.J.Thomson (1856-1940)1. Proposed the first model of the atom.2. 1897- Thomson discovered the electron(negatively- charged) – cathode rays3. Thomson suggested that an atom is apositively- charged sphere with electronsembedded in it.

Ernest Rutherford (1871-1937)1. 1914- Rutherford discovered the proton2. Rutherford model was based on the alphaparticle scattering experiment3. He proposed1) all the positive charge of an atom isconcentrated in the nucleus2) an atom consists of a positively-chargednucleus with a cloud of electrons surroundingthe nucleus

Neils Bohr (1885-1962) He was a student of Rutherford He proposed1) electrons are arranged in orbits (electronshells) around the nucleus of the atom2) electrons move in a particular path, have afixed energy. To move from one orbit to another, an electronmust gain or lose the right amountof energy

Atom Overview ATOM- is the smallest particle of an element thatmaintains the characteristics of that element ELEMENT- is a pure substance that cannot be splitup into 2 or more simpler substances by chemicalprocesses Atom is made up: NucleusElectron cloud or shells Nucleus and electron cloud consists of 3 subatomic particles: Protons Neutrons Electrons

What is an atom made of? The Nucleus– Protons Positively charged particles in the nucleus– Neutrons Particles of the nucleus that have no electricalcharge Electron cloud/ shells– Electrons Negatively charged particles in atoms Found around the nucleus within electron clouds

Sub-atomic ParticlesParticleChargeMass (g)LocationElectron(e-)-19.11 x 10-28ElectroncloudProton(p ) 11.67 x 10-24NucleusNeutron(no)01.67 x 10-24Nucleus

Atomic Number Atoms are composed of identical protons,neutrons, and electrons– How then are atoms of one elementdifferent from another element? Elements are different because they containdifferent numbers of PROTONS The atomic number of an element is thenumber of protons in the nucleus # protons in an atom # electrons

Atomic NumberAtomic number (Z) of an element is thenumber of protons in the nucleus of each atomof that element.Element# of protonsAtomic # (Z)Carbon66Phosphorus1515Gold7979

Mass NumberMass number (A) is the number of protons andneutrons in the nucleus of an element:Mass # p n0p n0e- Mass #810818Arsenic - 7533423375Phosphorus - 3115161531NucleusOxygen - 18

Complete Symbols Contain the symbol of the element,the mass number and the atomicnumber.MassSuperscript numberSubscript AtomicnumberX

Symbol Form written in symbol formMassnumberAtomicnumber3517Cl symbol tells us that the atomooooosymbol ofthe elementis of element chlorinehas atomic number 17 (so it contains 17 protons)has 17 electrons (number of protons number ofelectrons)has mass number 35 (so number of protons numberof neutrons 35)it must contain 35 – 17 18 neutrons

Symbols Find each of these:a) number of protonsb) number ofneutronsc) number ofelectronsd) Atomic numbere) Mass Number8035Br

Symbols If an element has an atomicnumber of 34 and a massnumber of 78, what is the:a) number of protonsb) number of neutronsc) number of electronsd) complete symbol

Isotopes Atoms of an element that have the samenumber of protons and electrons ,butdifferent numbers of neutrons.– Hydrogen isotopes Hydrogen has 1 proton, 1 electron and 0 neutrons Deuterium has 1 proton, 1 electron and 1 neutron– Therefore, it is heavier than hydrogen but has similar chemicalproperties and slightly different physical properties Tritium has 1 proton, 1 electron and 2 neutrons23Isotopes11Na2411Nanumber of protons1111number of electronsnumber of neutrons1123 - 11 121124 – 11 13

Ions Ion – electrically charged particle Thus, atoms whose # of electrons does NOTEQUAL the # of protons Either positively or negatively charged Positively charged loses one or moreelectrons Negatively charged gains one or moreelectrons Determining the charge of an ion:Overall charge # of protons - # of electrons

Includes:––––Symbol for IonsAtomic numberMass numberElement symbolCharge Example:– 35 protons, 45 neutrons, 36 electrons80Br-135– 12 protons, 12 neutrons, 10 electrons2412Mg 2

The Periodic Table In 1869,Dmitri IvanovitchMendeléev created the firstaccepted version of the periodictable. He grouped elements accordingto their atomic mass, and as hedid, he found that the groups hadsimilar chemical properties. Blank spaces were left open toadd the new elements hepredicted would occur.

The Periodic Table Periodic Law - When the elements arearranged in order of increasing atomicnumber, there is a periodic repetition of theirphysical and chemical properties Modern Periodic consists of: Periods - Horizontal rows of the periodic table(side to side) Groups or families - – vertical (up and down)column of elements in the periodic table

The Periodic Table Groups – Arranged by the # of valence electronsi.e. # of electrons in the outer shell– Elements in the same group has same # of valenceelectrons– Each group has similar chemical and bondingproperties– 8 groups Periods – Arranged by increasing atomic number– Elements in a period have the same number ofelectronic shells– 7 periods

Periodic Table128345 67Groups go downon the periodictableElements in thesame group, havethe same numberof valenceelectrons

Periodic Table1234567Periods goacross on theperiodic tablePeriods have thesame number of“shells”

Arrangement of electrons in the atom Electrons are arranged in energy levels i.e.Electron shells, around the nucleus Each energy level can only hold a certain # ofelectrons

Arrangement of electrons in the atom Main rule – electrons always go into the shellnearest to the nucleus, if the is room. Once theshell is filled up, the electrons go into the nextavailable shell. Outermost shell of an atom is called the valenceshell This shell should have electrons before it can becalled a valence shell The electrons in the valence shell are called thevalence electrons

The Electronic Configuration of AtomsO168Atomicnumber(Proton)Mass number(Nucleon)O

The Electronic Configuration of AtomsMg

Groups Columns of elements are called groups orfamilies. Elements in each group have similar but notidentical properties. All elements in a group have the same number ofvalence electrons. Include:– Group A: Alkali metals, alkali earth metals, boron,carbon, nitrogen, oxygen, halogens and noble/inertgases– Group B: transition metalslanthanides and actinides (inner transitionmetals)

Hydrogen The hydrogen found on top group I, but it isnot a member of that group Hydrogen is in a class of its own It’s a colourless gas at room temp Diatomic, reactive gas It has one proton and one electron in its oneand only energy level. Promising alternative fuel source

Alkali Metals The alkali family is found in the first column of the periodictable. Atoms of the alkali metals have a single electron in theiroutermost level, in other words, 1 valence electron. Tend to lose 1 electron (form 1 ions) Alkali metals are never found as free elements in nature. Theyare always bonded with another element. They are shiny, have the consistency of clay, and are easily cutwith a knife. Highly reactive, stored under oil Density less than water mp and bp are very low comparedto other metals

Alkaline Earth Metals 2 valence electrons Tend to lose the 2 electrons (form 2 ions) They are always combined with non-metals in nature e.g. metaloxides They have two valence electrons. Alkaline earth metals include magnesium and calcium, amongothers. Several are important mineral nutrients e.g Ca and Mg

Boron FamilyElements in group 33 valence electronsExists as both non-metals and metalsMetallic character increases down the groupAl used to produce many products e.g. cans, car body partsetc. Ga used in computer chips

Carbon Family Elements in group 44 valence electronsExists as both non-metals and metalsMetallic character increases down the groupCarbon important element for all living organisms, formbasis of branch of organic chemistrySilicon is a metalloid and is also abundant e.g. sandGermanium is a metalloid, used in electronics as semiconductorsTin and Lead are metals, with high densitiesPb used in nuclear reactors and protection againstradioactive materials

Allotropes of CAmorphous CGraphite(Sheets)Diamond(Network Solid)

Nitrogen Family Elements in group 55 valence electronsNitrogen makes up over ¾ of the atmosphereN2 is exist in diatomic statePhosphorous exist in two forms – white and redP used in explosives and in the manufacture offertilizers

Oxygen (Chalcogens) FamilyElements in group 66 valence electronsTend to gain 2 electrons (form -2 ions)Oxygen is a diatomic gas, essential for lifeSulfur is a solid, yellow non-metal – used in themanufacture of various chemical products e.g. sulfuricacid, paints etc. Se is a metal – good conductor and light sensitive, usedin solar cells and photocopy machines Te and Po are metalloids – radioactive

Halogens Family Elements in group 7 7 valence electrons Most reactive non-metal elements, tend to gain 1electron (form -1 ions) Found in combination with other elements in naturee.g. NaCl Used to manufacture different products –disinfectants, bleach, plastic etc. F and Cl are gases, Br is liquid, I and At are solid

Noble/Inert Gases Elements in group 8Have filled valence shell, overall charge is zeroUnreactive (inert), monoatomic gasesAll are colourless, tasteless and odourlessHe is less dense than air, used in balloonsNe used in advertising lights, glowsRadon is radioactive

Transition Metals Include elements in group B Arrangement of e- in outer shell vary, so the ioncharge changes Lose diff # of valence e-, depending on the rxn Therefore, degree of reactivity and properties variesby element Two categories:– Main transition metals e.g. Cu, Sn, Fe, Au, Ag– Inner transition metals Lanthanides and Actinides Know the uses of some ofthe common metals

Division of the Periodic Table Different types of elements are found ondifferent parts of the table 3 main classification:– Metals to the left (majority of the elements).– Nonmetals to the right (18 elements).– Metalloids found on a “staircase” dividingmetals and nonmetals (7 elements). Lanthanides & Actinides (metals) added to bottom tomake table manageable.

Metals Lustrous (shiny) Malleable (can be pounded into thinsheets) Ductile (can be pulled into wires) Conductive– Heat and electricity Solids (except mercury)High density, Mp and BpReact with O2 to form oxidesReact with H2O to form metal hydroxidesReact with acids to form Hydrogen gas. Uses: building structures, electric cables,radiators, colored paints, catalysts for industrialreactions, etc.

Reactivity of Metals

Minerals and Ores Unreactive metals are found innature in their elemental state i.e.free Most metals found in nature in theform of minerals and ores Minerals – naturally occurringinorganic solids with a definitecrystal structure Ores – concentrations of mineralsin rock, that are high enough to beextracted (mining) for economicuse– All ores are minerals, but not allminerals are ores

Alloys Mixture of two or more metalelements Mixture or alloy has differentproperties from those of thecomponent elements Property is dependant on the typesand amount of individual metalsused. Common alloys include:––––Sterling silver (Ag, Cu)Brass (Zn, Cu)Stainless Steel (Fe, Cr, Ni)Duralium (Al, Cu)

Non-metals Wide range of properties, opposite tothat of metals Tend to:Be DullPoor conductorsGain e- during reactionsMany are gases at room tempSome are brittle solids e.g. sulfurBromine only non-metalwhich is liquid at room temp– Not react with acids– Have lower melting & boiling points.––––––

Metalloids Also called “semi-metals” or“staircase elements.” Combination of properties ofmetals and nonmetals. Boron, Silicon, Germanium,Arsenic, Antimony, Tellurium, &Polonium Many exhibit semi-conductingbehavior.

THE END

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Metallic Bonding