The Atom Chapter 2

Atom: basic unit of matter Smallest unit of matter that individually retains the chemical characteristics of an element Consists of a dense 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 u = 1.66 x 10–24 g 1/12 the weight of a Carbon- 12 atom

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

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 u

Plum Pudding Model J.J. Thomson 1904

Gold Foil Experiment Ernest Rutherford 1909 Proved J.J. Thomson’s theory wrong Evidence for existence of protons

The Modern Atom We know atoms are composed of three main pieces—protons, neutrons, and electrons. The nucleus contains protons and neutrons. The nucleus is only about 10-13 cm in diameter. The electrons move outside the nucleus with an average distance of about 10-8 cm. Therefore, the radius of the atom is about 105 times larger than the radius of the nucleus. Tro's "Introductory Chemistry", Chapter 4

2.2 Structure of the Atom All matter is composed of the same basic building blocks called atoms. Atoms are composed of three subatomic particles:

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

Mendeleev's Predictions for Ekasilicon (Germanium) Tro's "Introductory Chemistry", Chapter 4

= Alkali metals = Alkali earth metals = Noble gases = Halogens = Lanthanides = Actinides = Transition metals add pictures of elements from text Tro's "Introductory Chemistry", Chapter 4

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), Polonium (Po), Astatine (At)

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

Which atom does the picture below represent?

Atomic # # of protons Atomic symbol Atomic Mass Atomic Weight Mass # Molar Mass

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

Ions Atoms acquire a charge by gaining or losing electrons. Not protons! Ion charge = # protons – # electrons. Ions with a positive charge are called cations. More protons than electrons. Form by losing electrons. Ions with a negative charge are called anions. More electrons than protons. Form by gaining electrons. Chemically, ions are much different than the neutral atoms. Because they have a different structure. Tro's "Introductory Chemistry", Chapter 4

Atomic Structures of Ions Nonmetals form anions. For each negative charge, the ion has 1 more electron than the neutral atom. F = 9 p+ and 9 e; F─ = 9 p+ and 10 e. P = 15 p+ and 15 e; P3─ = 15 p+ and 18 e. Anions are named by changing the ending of the name to –ide. fluorine F + 1e  F─ fluoride ion oxygen O + 2e  O2─ oxide ion The charge on an anion can often be determined from the group number on the periodic table. Group 7A  1, Group 6A  2. Tro's "Introductory Chemistry", Chapter 4

Atomic Structures of Ions, Continued Metals form cations. For each positive charge the ion has 1 less electron than the neutral atom. Na atom = 11 p+ and 11 e; Na+ ion = 11 p+ and 10 e. Ca atom = 20 p+ and 20 e; Ca2+ ion = 20 p+ and 18 e. Cations are named the same as the metal. sodium Na  Na+ + 1e sodium ion calcium Ca  Ca2+ + 2e calcium ion The charge on a cation can often be determined from the group number on the periodic table. Group 1A  1+, Group 2A  2+, (Al, Ga, In)  3+. Tro's "Introductory Chemistry", Chapter 4

Isotopes Atoms of the same element that have different atomic masses Same number of protons Different # of neutrons

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

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)

If it is a neutral atom, it will have 20 electrons. Practice—An Atom Has 20 Protons. Determine if Each of the Following Statements Is True or False? If it is a neutral atom, it will have 20 electrons. If it also has 20 neutrons, its mass will be approximately 40 amu. If it has 18 electrons, it will have a net 2 charge. True True False Tro's "Introductory Chemistry", Chapter 4

Review What is the atomic number of boron, B? What is the atomic mass of silicon, Si? How many protons does a chlorine atom have? How many electrons does a neutral neon atom have? Will an atom with 6 protons, 6 neutrons, and 6 electrons be electrically neutral? Will an atom with 27 protons, 32 neutrons, and 27 electrons be electrically neutral? Will an Na atom with 10 electrons be electrically neutral?

Review What is the atomic number of boron, B? 5 What is the atomic mass of silicon, Si? 28.09 amu How many protons does a chlorine atom have? 17 How many electrons does a neutral neon atom have? 10 Will an atom with 6 protons, 6 neutrons and 6 electrons be electrically neutral? Yes Will an atom with 27 protons, 32 neutrons, and 27 electrons be electrically neutral? Yes Will an Na atom with 10 electrons be electrically neutral? No Tro's "Introductory Chemistry", Chapter 4

Practice—Complete the Following Table. Tro's "Introductory Chemistry", Chapter 4

Practice—Complete the Following Table, Continued. Tro's "Introductory Chemistry", Chapter 4

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 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

Atomic Orbitals Orbital: a specific region in an atom thought to posses the highest probability of containing the electron in question at any one time Only hold maximum of two electrons at a time 4 basic types: s, p, d, f

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.

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

2.6 Electron Configuration B. Second-Row Elements (Period 2) Orbital Notation Electron Configuration Element Li (Z = 3) 3 electrons 1s22s1 1s 2s C (Z = 6) 6 electrons 1s22s22p2 1s 2s 2p Ne (Z = 10) 10 electrons 1s22s22p6 1s 2s 2p

2.6 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. Electron Configuration Noble Gas Notation element: C 1s22s22p2 [He]2s22p2 nearest noble gas: He 1s2

2.6 Electron Configuration C. Other Elements Orbital Notation Element Ca 20 electrons 1s 2s 2p 3s 3p 4s 4s is lower in energy; it is filled before 3d. Electron Configuration Noble Gas Notation 1s22s22p63s23p64s2 [Ar]4s2

Problems Determine the electron configurations for the following atoms. Use the noble gas configuration if needed. N O Ne Na Mg Al S Fe W

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

2.8 Periodic Trends A. Atomic Size The size of atoms increases down a column, as the valence e− are farther from the nucleus. Increases Decreases The size of atoms decreases across a row, as the number of protons in the nucleus increases, pulling the valence electrons in closer.

2.8 Periodic Trends B. Ionization Energy The ionization energy is the energy needed to remove an electron from a neutral atom. Na + energy Na+ + e– Decreases Ionization energies decrease down a column as the valence e− get farther away from the positively charged nucleus. Increases Ionization energies increase across a row as the number of protons in the nucleus increases.