The Atom Chapter 2 Chem2A

Elements An element is a pure substance that cannot be broken down into simpler substances by a chemical reaction. Consists of a dense core, surrounded by a negatively charged cloud Contains three types of subatomic particles Proton Neutron Electron

The Proton Charge = +1.602x10-19 C Located in the nucleus Mass = 1.672 x 10-24 g ~1 atomic mass unit (amu) 1 amu = 1.66 x 10-24 g 1/12 the weight of a 12C atom

The Neutron No charge (O C) Located in the nucleus Mass = 1.675 x 10-24 g ~1 amu

The Electron Charge = -1.602 x 10-19 C Located outside the nucleus in an e- “cloud” Mass = 9.109 x 10-28 g ~0 amu

Plum Pudding Model J.J. Thomson 1904

Gold Foil Experiment Ernest Rutherford 1909

Thomson vs. Rutherford Rutherford used the angle of deflection to calculate size of the nucleus Nucleus approximated at 10,000 times smaller than the radius of the atom Atom is actually mostly empty space

Atoms

Periods  

Groups

Periodic Table of Elements

Classification of Periodic Table

Elements and Symbols C = Carbon N = Nitrogen O = Oxygen Cl = Chlorine Ba = Barium U = ? Cf = ? Bk = ? Md = ? Es = ?

K = Pb = W = Sb = Co = Cu = Cr = Mg = Mn =

Metals Shiny Conduct Electricity Ductile Malleable (Shapeable) Can be drawn into a thin wire Malleable (Shapeable) High M.P. and B.P. Solids @ RT Except Hg

Non-Metals Don’t conduct well Not usually ductile Brittle Low M.P. and B.P. Many are gasses at RT

Metalloids Chemical characteristics in between metals and non-metals Includes all atoms falling on the dividing line between metals and non metals

Classification of Periodic Table

Alkali Metals Group 1 (1A) Li, Na, K etc. Soft, shiny metals Conduct heat and electricity React violently with H2O Form H2(g) and alkaline (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 3-12 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 13(3A) – 16(6A) No common name Boundary between metals and non-metals occurs here Contain elements abundant in earth’s crust, atmosphere, and living things Contains the metalloids

Halogens Group 17 (7A) Love to form salts with metals NaCl, KBr, CaCl2 Like to form diatomic molecules F2, Cl2, Br2

Noble Gases Group 18 (8A) Very unreactive Don’t like to bond to other molecules Generally not abundant

Diatomic Molecules Dinitrogen (N2) Molecules consisting of only two atoms of either the same or different elements O2 CO Homonuclear Diatomic Molecule: a molecule made of two atoms of the same element H2 Heteronuclear Diatomic Molecule: a molecule made of two atoms that are different elements NO

Allotropism The existence of multiple pure forms of an element, in the same phase (solid, liquid, or gas), that differ in structure Different forms are called allotropes Can exhibit varied physical properties and chemical behaviors Don’t confuse allotropes with isotopes!!! O2 O3

2.2 Structure of the Atom From the periodic table: Atomic Number = # of protons Atomic Symbol Atomic Mass Any given element is neutral # of protons (+) = # of electrons (-) # of neutrons = Atomic Mass (rounded) - # Protons 7 – 3 = 4 neutrons

Problems H C Fe Pd W Atomic Weight # Protons # Electrons # Neutrons

Calculator Boot Camp

2.3 Isotopes A. Isotopes, Atomic Number, and Mass Number Isotopes are atoms of the same element that have a different number of neutrons. the number of protons (Z) Mass number (A) = + the number of neutrons Mass number (A) 35 37 Mass number (A) Cl Cl Atomic number (Z) 17 17 Atomic number (Z) # of protons = 17 # of protons = 17 # of electrons = 17 # of electrons = 17 # of neutrons = 35 – 17 = 18 # of neutrons = 37 – 17 = 20

Identify the atomic mass, number of protons, and number of neutrons for the following elements.

2.3 Isotopes B. Atomic Weight The atomic weight is the weighted average of the masses of the naturally occurring isotopes of a particular element reported in atomic mass units. From the periodic table: 6 C 12.01 atomic number element symbol atomic weight (amu)

2.3 Isotopes B. Atomic Weight HOW TO Determine the Atomic Weight of an Element What is the average atomic weight of chlorine? Example List each isotope, its mass in atomic mass units, and its abundance in nature. Step [1] Isotope Mass (amu) Isotopic Abundance Cl-35 34.97 75.78% = 0.7578 Cl-37 36.97 24.22% = 0.2422

2.3 Isotopes B. Atomic Weight HOW TO Determine the Atomic Weight of an Element Multiply the isotopic abundance by the mass of each isotope, and add up the products. Step [2] The sum is the atomic weight of the element.

Using the percent abundances below, calculate the average atomic mass for Carbon Antimony (Sb) has two stable isotopes, 121Sb and 123Sb with masses of 120.9038 u and 122.9042 u, respectively. Calculate the percent abundances of these two isotopes

Atomic Orbitals and Electron Configurations

The shells are numbered n = 1, 2, 3, etc. Electronic Structure Electrons are confined to discrete regions called shells 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.

Electronic Structure Shells with larger numbers (n) are farther from the nucleus and can hold more electrons. # of electrons in each shell is calculated using 2(n2), where n = shell number. Number of Electrons in a Shell Shell (n) 4 32 3 18 increasing number of electrons increasing energy 2 8 1 2

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 Contains 1 orbital: s 1 orbital can hold 2 electrons MAX = 2 electrons max

P Orbitals The p orbital has a dumbbell shape Higher energy than S Orbitals 3 separate orbitals px, py, pz Each orbitals can hold 2 electrons MAX = 6 electrons max

D Orbitals Double dumb bell shape or single dumb bell with a donut Higher energy than s and p 5 orbitals dxy, dxz, dyz, dx2-y2, dz2 = 10 electrons max

F Orbitals Complex Shapes Highest Energy Orbital 7 Orbitals =14 electrons max

Electronic Structure

Electron Configuration The electron configuration shows how the electrons are arranged in an atom’s orbitals. The ground state is the lowest energy arrangement. Rules to Determine the Ground State Electronic Configuration of an Atom Rule [1] Electrons are placed in the lowest energy orbital beginning with the 1s orbital. Orbitals are then filled in order of increasing energy.

Electron Configuration Rules to Determine the Ground State Electronic Configuration of an Atom

Electron Configuration Rules to Determine the Ground State Electronic Configuration of an Atom Rule [2] Each orbital holds a maximum of 2 electrons. Rule [3] When orbitals are equal in energy: 1 electron is added to each orbital until all of the orbitals are half-filled. Then, the orbitals can be completely filled.

Electron Configuration Orbital Diagrams An orbital diagram uses a box to represent each orbital and arrows to represent electrons. an orbital a single, unpaired electron an electron pair Two electrons must have paired spins (opposite directions) to fit into the same orbital.

Electron Configuration A. First-Row Elements (Period 1) Orbital Notation Electron Configuration Element H (Z = 1) 1 electron He (Z = 2) 2 electrons

Electron Configuration B. Second-Row Elements (Period 2) Orbital Notation Electron Configuration Element Li (Z = 3) 3 electrons C (Z = 6) 6 electrons Ne (Z = 10) 10 electrons

Problems Determine the electron configuration and orbital diagrams for the following atoms N O Na Mg Fe W

Electron Configuration The electron configuration can be shortened by using Noble Gas Notation. Write the Symbol of the previous Noble Gas, then add the electronic configuration of the additional electrons. element: C previous noble gas:

Electron Configuration C. Other Elements Ca 20 electrons

Electron Configurations and the Periodic Table

2.7 Valence Electrons The chemical properties of an element depend on the number of electrons in the valence shell. The valence shell is the outermost shell (the highest value of n). The electrons in the valence shell are called valence electrons. Be Cl 1s22s2 1s22s22p63s23p5 valence shell: n = 2 valence shell: n = 3 # of valence electrons = 2 # of valence electrons = 7

2.7 Valence Electrons A. Relating Valence Electrons to Group Number Elements in the same group have similar electron configurations. Elements in the same group have the same number of valence electrons. The group number, 1A–8A, equals the number of valence electrons for the main group elements. The exception is He, which has only 2 valence electrons. The chemical properties of a group are therefore very similar.

2.7 Valence Electrons A. Relating Valence Electrons to Group Number Period 1: H 1s1 He 1s2 Period 2: Li 2s1 Be 2s2 B 2s22p1 C 2s22p2 N 2s22p3 O 2s22p4 F 2s22p5 Ne 2s22p6 Period 3: Na 3s1 Mg 3s2 Al 3s23p1 Si 3s23p2 P 3s23p3 S 3s23p4 Cl 3s23p5 Ar 3s23p6

Valence Electrons B. Electron-Dot Symbols Dots representing valence electrons are placed on the four sides of an element symbol. Each dot represents one valence electron. For 1 to 4 valence electrons, single dots are used. With more than 4 valence electrons, the dots are paired. Element: H C O Cl # of Valence electrons: 1 4 6 7 Electron-dot symbol: H C O Cl

Periodic Trends A. Atomic Size The size of atoms increases down a column Increases Decreases The size of atoms decreases across a row

Chapter 2 Review The periodic table will be folded up for quiz and exam Know the names and elemental symbols of s block, p block, and select d block atoms W, Cu, Ag, Fe, Hg, Ti

Chapter 2 Review Know how to classify atoms as metals, non-metals, and metalloids. Know the period classifications Alkali, Alkaline, Transition Metals, main block, halogens, noble gas

Classification of Periodic Table 13 Al 84 Po

Chapter 2 Review Location, and charge of the 3 particles that make up an atom Proton (nucleus), Neutron (nucleus), Electron (diffuse cloud surrounding nucleus) Determining how many protons, neutrons and electrons an atom has

Chapter 2 Review Orbitals s, p, d, f Know everything about s and p Know how many electrons all can have Know how they relate in energy

Chapter 2 Review What are isotopes How do isotopes relate in terms of weight How to calculate the average atomic weight

Chapter 2 Review Know how to fill in (yes ill give you boxes) molecular orbitals Know how to write noble gas abbreviations for any atom

Chapter 2 Review Know what valence electrons are and how to ID them in an electron configuration Know the relationship between atoms in the same period Know how to write electron dot symbols