The Atom Chapter 2

The Atom Chapter 2

Chapter 2: Atoms and Elements Chapter 2 Goals and Homework Focus on atoms/elements/compounds Look inside an atom Become familiar with the periodic table of elements Classify different types of elements Perform calculations with elements Understand atomic orbitals and electron configurations and their rules

Valence electrons and dot structures Periodic Trends Homework 35, 37, 39, 43, 45, 47, 49, 57, 59, 65, 69, 73, 83, 85, 91, 93 Elements and Symbols Element Pure substance that can not be broken down into simpler substances by a chemical reaction 1 letter symbols C = Carbon

N = Nitrogen O = Oxygen 1 Capital letter 2 letter symbols Cl = Chlorine Ba = Barium Au = Gold 1 Capital and 1 lower

case letter Compound Pure substance formed by chemically combining two or more elements H element + O element can make H2O compound CO2, HCl, C3H8 Atom smallest unit of an element Molecule smallest unit of a compound

Atom: basic unit of matter Smallest unit of matter that individually retains the chemical characteristics of an element Consists of a dense positively charged central region, called a nucleus, surrounded by a negatively charged cloud Contains three types of subatomic particles:

Proton Neutron Electron The Proton Charge = + 1.6021019 C Called +1 for clarity Located in nucleus of atom Mass = 1.672 x 1024 g Approx. 1 unified atomic mass unit (u)

1 amu = 1.66 x 1024 g The Neutron No charge (0 C) Located in nucleus Mass = 1.675 x 1024 g Approx. = 1 amu The Electron Charge = 1.602 x 1019 C Called 1

Located outside nucleus in an ecloud Mass = 9.109 x 10-28g Approx. = 0 amu Recap What are the three subatomic particles? Where are they located in the atom? What are their weights in atomic mass units What are their charges? Dmitri Mendeleev

(1834-1907) Russian chemist Arranged elements in horizontal rows in order of increasing atomic weight Started new rows in order to make columns of chemicals with similar characteristics Left spaces open for elements yet to be discovered Classification of the Periodic Table

Classification by Physical Properties Metals Shiny Conduct electricity Ductile Can be drawn through wires Malleable (Shapeable) High M.P. & B.P

Solids @ room temp Except Hg Non-Metals Dont tend to conduct well Not usually ductile Tend to be brittle Low M.P. & B.P. Many are gases at r.t.

Metalloids Have chemical characteristics in between those of metals and nonmetals Includes elements: B (Boron), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), Astatine (At) Classification by Chemical Properties

Alkali Metals Group 1 (1A) Li, Na, K etc.

Soft, shiny metals Conduct heat and electricity React violently with H2O Form H2(g) and (basic) solutions Akali(ne) Earth Metals

Group 2 (2A) Be, Mg, Ca etc. Not as reactive as Alkali Metals, but still quite reactive Tend to make basic solutions when placed in water Transition Metals Groups 3B-8B Tend to have high densities and B.P. All are metals

Often used for electrical conduction Often have vivid colors when in solution Used for pigments Colors of Transition Metal Compounds Iron

Cobal t Nicke l Copper Zin c

Lanthanides Elements 57-71 Lanthanum (La) to Lutetium (Lu) Commonly used in lasers Can deflect UV and infrared rays Actinides/Actinoids Elements 89-103

Actinium (Ac) to Lawrencium (Lr) Only Actinium, Thorium (Th), and Uranium (U) occur naturally Others created by neutron bombardment Radioactive Groups 3A 6A No common name

Boundary between metals and non-metals occurs here Contains the metalloids Contain elements abundant in earths crust, atmosphere, and living things C, N, O, Si Halogens

Group 7A F, Cl, Br, I, At Very reactive with many compounds Like to form diatomic molecules F2, Cl2, Br2, Noble Gases Group 8A

He, Ne, Ar, Kr, Xe, Rn Very unreactive Dont like to bond to other molecules Generally not abundant Problems Write down an element from each of the groups

1. Noble Gas (example-- He aka Helium) 2. Lathanide 3. Alkali metals 4.Halogens 5. Actinides 6. Alkaline metals 7. Element that is abundant in living organisms Atomic number -- Also number of

protons -- Usually the number of electrons as well Atomic symbol -- 1 or 2 letter symbol Average atomic weight or Approximate Mass number -- Also number of

protons + number of neutrons Can also represent by omitting atomic number (Z) since it is implied by the element Which atom does the picture below represent? Chapter so far recap What is matter?

Atom is smallest unit of matter What is an atom made of? What is the periodic table of elements What are the different classifications of elements by physical properties? Or by chemical properties? Atomic number = Z, Mass number = A, Neutron number = N Identify number of protons, the mass number, and number of neutrons for the following elements.

Isotopes Atoms of the same element that have different atomic masses Same number of protons Different # of neutrons Percent Abundance - amount of each isotope that occurs naturally Average atomic mass

Weighted average of the mass of naturally occurring isotopes of a particular element reported in atomic mass units Zi = mass number (mass in amu) of smallest isotope % abd = percent abundance [Zi(% abd) + Zi+1(% abd) + Zi+2(% abd) + ]=Zamuaverage Example-- [20(0.9092) + 21(0.0026) +22(0.0882)] = 20.179 amu ~ 20.18 amu

Problems 1) Lithium has two natural isotopes, 6Li and 7 Li, which have percent abundances of 7.5% and 92.5% respectively. What is the average atomic mass of Lithium? 6

Li 6amu 7 Li 7 amu Li 6 6 Li % abd 7.5% 0.075

7 Li % abd 92.5 0.925 Li 7 (6amu (0.075)) (7amu (0.925)) ? amu (0.45) (6.48) 6.93amu 2) Using the percent abundances below, calculate the

average atomic mass for Carbon from its three isotopes C-12 = 98.890% C-13 = 1.110% C-14 = 0.0000000001% C-12 C-13 C-14

(12amu (0.9889)) (13amu (0.01110 )) (14amu (0.000000000001)) ? amu (11.87amu ) (0.1443amu ) (approximat ely 0amu ) 12.01amu 3) Antimony (Sb) has two stable isotopes, 121Sb and 123Sb with masses of 120.9038 amu and 122.9042 amu, respectively. Calculate the percent abundances of these two isotopes 121

Sbamu 120.9038amu 123 Sbamu 122.9042amu 123 Sb%abd ,121 Sb%abd ? Sbamuaverage 121.76amu

(121 Sbamu121 Sb%abd ) (123 Sbamu123 Sb%abd ) Sbamuaverage 121 Sb%abd 123 Sb%abd 100% 1.00 123 Sb%abd 1.00 121 Sb%abd (121 Sbamu121 Sb%abd ) (123 Sbamu(1.00 121 Sb%abd )) Sbamuaverage

(121 Sbamu121 Sb%abd ) (123 Sbamu(1.00 121 Sb%abd )) Sbamuaverage (121Sbamu121 Sb%abd ) (123 Sbamu 123 Sbamu121 Sb%abd ) Sbamuaverage 121 Sbamu121 Sb%abd 123 Sbamu 123 Sbamu121 Sb%abd Sbamuaverage 121 Sbamu121 Sb%abd 123 Sbamu121 Sb%abd Sbamuaverage 123 Sbamu 121

Sb%abd (121Sbamu 123 Sbamu) Sbamuaverage 123 Sbamu 121 121 Sb%abd 123 123 Sb%abd

(Sbamuaverage 123 Sbamu) (121 Sbamu 123 Sbamu) (121.76amu 122.9042amu) 0.57198 57.198% (120.9038amu 122.9042amu) Sb%abd 1.00 121 Sb%abd Sb%abd 1.00 0.57198 0.42802 42.802%

Atomic Orbitals and Electron Configurations 2.5 Electronic Structure An electron is confined to a specific region around the nucleus, giving it a particular energy. The regions occupied by electrons are called principal energy levels or shells (n). The shells are numbered n = 1, 2, 3, etc. Electrons in lower numbered shells are closer to the nucleus and are lower in energy.

Electrons in higher numbered shells are further from the nucleus and are higher in energy. 44 2.5 Electronic Structure Shells are divided into subshells, identified by the letters s, p, d, and f. The subshells consist of orbitals. An orbital is a region of space where the probability of finding an electron is high. Each orbital can hold two electrons.

increasing energy Subshell s p Number of Orbitals 1 3

d 5 f 7 45

S orbitals Spherical shape Lowest energy of the orbitals P Orbitals

Higher energy than s orbitals Dumb bell shaped Come in 3s p x , py , pz D Orbitals Higher energy than s and p orbitals Double dumb bell shape or single dumb bell with a donut Come in 5s

dxy, dxz, dyz, dx2-y2, dz2 F Orbitals Higher energy than s, p, and d Come in 7s How do we know where our electrons are? Electrons will seek the lowest E orbital available first Hydrogen

1 Helium Lithium? Pauli Exclusion Principle: orbitals may hold up to two electrons. The electrons must be of opposite spin Hunds Rule: electrons pair only after each orbital of equal energy is occupied by a single electron Determine the electron

configurations for the following atoms 1) 2) 3) 4) 5) 6) 7) 8) 9)

N O Ne Na Mg Al S Fe W

Noble Gas Abbreviation The electron configuration of the noble gas that precedes the element in question is represented by the noble gas bracketed symbol Example: C = 1s22s22p2 = [He] 2s22p2 Write the electron configurations for Vanadium and Bismuth Valence Electrons

Electrons in the outermost(valence) shell The shell with the highest number C = 1s22s22p2 --- 2 is highest number count up electrons in all the valence orbitals 2 electrons in the 2s orbital and 2 electrons in the 2p orbital 2 + 2 = 4 valence electrons P = 1s22s22p63s23p3 ------- 3 is highest number 2 + 3 = 5 valence electrons Using the Noble gas abbreviation can help

Electron dot symbols Valence electrons represented with dots Dots are placed on four sides of the element symbol Up to 2 dots max per side, must fill up all sides before pairing up dots Li Valence Electrons 1 Be

B C N O F

Ne 2 3 4 5 6

7 8 Problems Determine valence electrons for the following elements and draw the electron dot symbol for each 1. H 2. Li

3. Si 4. Br 5. Ar 6. Ti Periodic Trends Atomic number increases going to the right and going down Atomic size (how big the atom is) increases going to the left and going down Ionization energy (energy required to remove a valence

electron) increases going to the right and going up Chapter 2 Review Element symbols Inside the atom. Proton, neutron, and electron. Charge, mass, location. Periodic Table Bonanza!! Being familiar with the table and how to use it. Metals, metalloids, non metals. Properties and which elements are from which class. Group/families of elements. Alkali metals, Alkaline metals, transition metals, Halogens, Lanthanides, etc.

Atomic number and Mass number. Recognizing how many protons electrons and neutrons in an given isotope. Isotopes percent abundance. Calculating average atomic mass. Atomic orbitals. s, p, d, f orbitals, different shapes and energies. Electron configurations. Pauli exclusion principle, Hunds rule, noble gas, abbreviation. Valence electrons and Electron dot structure Periodic trends

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