IPC 03A Atoms & Elements

Atomic Structure History: John Dalton Dalton’s Atomic Theory: Proposed that elements are composed of identical, indivisible particles called atoms. The name “atom” comes from Democritus.

J.J. Thomson “Plum Pudding” Model He said the atom had electrons (raisins) immersed in a sea of positive charge (pudding).

J.J Thomson’s Cathode Ray Tube Experiment: He concluded that the cathode rays were made up of very small negatively charged particles, which he named electrons. + +   ee ee

Ernest Rutherford “Gold Foil” Experiment Discovered the positive-charged nucleus and that the atom is mostly empty space.

Rutherford’s Expectation (assuming the plum pudding model)  Rutherford expected positive alpha particles to go through the atom like in this picture.  

Rutherford’s Actual Results  Instead, Rutherford observed that some of the alpha particles bounced back;  Thus, he concluded there was a positive charged nucleus.  

Niels Bohr “Planetary Model” of the Atom  Nucleus is in the center.  Electrons orbit the nucleus.

Erwin Schrodinger “Electron Cloud Model”  The cloud represents the probable location of an electron.

James Chadwick Discovered the neutron.  There was still mass missing from the atom.  Chadwick solved the problem by discovering the final subatomic particle, the neutron. Jimmy Neutron

Exposing Scientist’s Contributions Atomic Theory John Dalton J.J. Thompson RutherfordJ. ChadwickNiels BohrSchrodinger

Atoms consist of three main Subatomic Particles Atomic mass unit (amu) = 1/12 the mass of a carbon-12 atom. Protons p+ Electrons e - Neutrons n 0 Mass Charge 1 amunone1 amu positivenegativeneutral

Structure of The Atom Nucleus is small, dense, and positively charged. Electrons are located outside the nucleus in an electron cloud.

Forces Within The Atom  Electromagnetic Forces keep the electrons in orbit around the nucleus. The negatively charged electrons are attracted to the positively charged protons in the nucleus.  Strong Nuclear Forces hold the nucleus together by opposing the force of repulsion between the positive charged protons so the nucleus won’t break apart. Only acts on very short distances.

Chemical Symbols  Elements are the simplest pure substance that cannot be changed into simpler substances.  Chemical symbols are an abbreviation of the element’s name.  The first letter is ALWAYS capitalized and the second letter is ALWAYS lower case! ElementSymbolOrigin CopperCuCuprium GoldAuAurium IronFeFerrium LeadPbPlumbum PotassiumKKalium SilverAgArgentum SodiumNaNatrium TinSnStannum

An Element- contains one type of atom with a unique number of protons. oToT he # of protons determines the element. oEoE x: Carbon has 6 protons. oIoI f you change the # of protons, you change the element. oEoE x: Nitrogen has 7 protons. Neutral Atoms have the same # of electrons as protons. Ex: neutral Carbon has 6 protons and 6 electrons

Element Notation Mass Number (M) - protons + neutrons –Found in the nucleus and makes of up most of the atom’s mass (99.99%). Atomic Number (A) - number of protons –Determines the element. X M A

Example: Carbon-12 1) What is the atomic number of Carbon? 2) What is the mass number of Carbon? C

Isotopes AA toms with the SS ame # of protons (same atomic #) DD ifferent # of neutrons DD ifferent mass # 3 n 0 4 n 0

Sodium Isotopes 1) Atomic number? 2) Mass number? 3) No. of Neutrons? 4) Atomic number? 5) Mass number? 6) No of Neutrons?

Hydrogen Isotopes Hydrogen-1 (Protium) Hydrogen-2 (Deuterium) Hydrogen-3 (Tritium)

Hydrogen Isotopes Fill in the #protons, #electrons, & #neutrons: Mass numberNo. of protons ↓ No. of electrons ↓ No. of neutrons ↓ Hydrogen-1 Hydrogen-2 Hydrogen (Mass #  # p + )

Atomic Mass – is the average mass of all the element’s natural isotopes. The most common isotope will have a mass no. of the atomic mass rounded to a whole no. Atomic number 47 Atomic Mass = amu The most common isotope of silver is Silver-108.

Mendeleev’s Periodic Table Dimitri Mendeleev – organized information about all the known elements by similarities and properties known as the periodic table of elements.

Periods (across) Groups (down) Groups & Periods Groups (Families) have similar properties and go down on the periodic table. There are 18 groups. Periods go across on the periodic table. There are 7 periods.

Identify the element in: Group 2 (IIA), period 4 Group 17 (VIIA), period 5 Group 11, period 4 Identify the element in: Group 2 (IIA), period 4 Group 17 (VIIA), period 5 Group 11, period 4 Ca Cu I Look at the Periodic Table:

Metals Nonmetals Metalloids Metals, Nonmetals, & Metalloids

Properties of metals and nonmetals Metalloids have both metallic and nonmetallic characteristics – along the staircase. Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Astatine MetalsNonmetals Luster (shiny silver-gray, gold, copper) Dull (all different colors) Malleable (hammered)Brittle Ductile (drawn into thin wire) Not ductile High Density & High Melting Points Low Density & Low Melting Points Good Conductors of heat & electricity Poor Conductors of heat & electricity Lose electronsGain electrons Silicon is used in computer chips because conduct electricity (metals) yet insulate (nonmetals).

Energy Levels in an Atom Electrons occupy energy levels around the nucleus. Each energy level can hold up to 2n 2 electrons where n = the energy level The farther away an electron is, the higher the energy it possesses.

Electrons in Energy Levels 1.What is the most common isotope? 2.How many protons? 3.How many electrons? 4.How many neutrons? 5.How many electrons in the 1 st energy level? 6.How many electrons in the 2 nd energy level? 7.How many electrons in the 3 rd energy level? Cl Cl

Absorption of Energy The electron absorbs enough energy causing the electron to be excited and “jump” to a higher unstable energy level. Energy e-

Emission of Energy The electron releases energy when it falls back to its lowest stable energy level (ground state) in the form of colored light. Energy e-

Example of Lithium

Atomic Emission Spectrum (hydrogen) Each line in the spectrum results from a different electron transition Red line Green line Blue line

Emission Spectrum: Iron (more e-) Carbon (less e-) Continuous Spectrum Each element has its own unique series of lines of colored light (‘fingerprint”)

Valence Electrons Electrons in the highest energy level Electrons used to form chemical bonds Group# of Valence Electrons 1A (1)1 2A (2)2 3A (13)3 4A (14)4 5A (15)5 6A (16)6 7A (17)7 8A (18)8

Octet Rule In order to become most stable, all atoms need 8 valence electrons in the outermost energy level. Noble gases already have 8 valence electrons which is why they are stable. Other elements gain or lose electrons by forming chemical bonds in order to have 8 valence electrons in the outermost energy level.

Oxidation Numbers Metals generally lose electrons to become more stable. –Metals form positive ions (charged atoms) Nonmetals generally gain electrons to become more stable. –Nonmetals form negative ions (charged atoms) GroupOxidation # 1A (1)+1 2A (2)+2 3A (13)+3 4A (14)±4 5A (15)-3 6A (16)-2 7A (17) 8A (18)0