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 1 letter symbols 1 Capital letter 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 = + 1.602×10−19 C Called “+1” for clarity Located in nucleus of atom Mass = 1.672 x 10–24 g Approx. 1 unified atomic mass unit (u) 1 amu = 1.66 x 10–24 g

The Neutron No charge (0 C) Located in nucleus Mass = 1.675 x 10–24 g Approx. = 1 amu

The Electron Charge = –1.602 x 10–19 C Called “–1” Located outside nucleus in an e- “cloud” 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 Don’t 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 non-metals 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 Nickel Cobalt Copper Zinc Iron

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 earth’s crust, atmosphere, and living things C, N, O, Si

Halogens Group 7A Very reactive with many compounds 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 Don’t 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 Period and group

-- Also number of protons 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 Lithium has two natural isotopes, 6Li and 7Li, which have percent abundances of 7.5% and 92.5% respectively. What is the average atomic mass of Lithium?

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

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

Atomic Orbitals and Electron Configurations

The shells are numbered n = 1, 2, 3, etc. 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.

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. Subshell Number of Orbitals s 1 increasing energy p 3 d 5 f 7

S orbitals Spherical shape Lowest energy of the orbitals

P Orbitals Higher energy than s orbitals Dumb bell shaped Come in 3’s px, py, pz

D Orbitals Higher energy than s and p orbitals Double dumb bell shape or single dumb bell with a donut Come in 5’s dxy, dxz, dyz, dx2-y2, dz2

F Orbitals Higher energy than s, p, and d Come in 7’s

How do we know where our electrons are? Electrons will seek the lowest E orbital available first

Hydrogen Helium Lithium? 1 Pauli Exclusion Principle: orbitals may hold up to two electrons. The electrons must be of opposite spin

Hund’s Rule: electrons pair only after each orbital of equal energy is occupied by a single electron

Determine the electron configurations for the following atoms 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

Problems Determine valence electrons for the following elements and draw the electron dot symbol for each H Li Si Br Ar 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