CHAPTER 2 Atoms and the Periodic Table General, Organic, & Biological Chemistry Janice Gorzynski Smith

CHAPTER 2: Atoms & the Periodic Table 2 Smith. General Organic & Biolocial Chemistry 2nd Ed. Learning Objectives:  Elemental Symbols  Metals vs Nonmetals vs Metalloids or Semimetals  Subatomic Particles: properties & location  Formulae of Compounds  Models to represent particles  Nucleus and structure of atom  Atomic number, Mass Number, Isotopes, Atomic Weight, & Atomic Mass  Periodic Table: groups & periods: similar properties within groups  Electron structure: valence electrons and electron dot symbols  Periodic trends: atomic size and ionization energy

3 Matter Definition

Matter Elements 4 Smith. General Organic & Biolocial Chemistry 2nd Ed. An element is a pure substance that cannot be broken down into simpler substances by a chemical reaction. Each element is identified by a one- or two-letter symbol. Elements are arranged in the periodic table. The position of an element in the periodic table tells us much about its chemical properties. diamond = carbongold sulfur

5 Matter Definition

Matter Compounds 6 Smith. General Organic & Biolocial Chemistry 2nd Ed. Compound: a pure substance formed by chemically combining two or more elements together. Element symbols to show the identity of the elements forming a compound. A chemical formula consists of: Subscripts to show the ratio of atoms in the compound. H2OH2O 2 H atoms1 O atom C3H8C3H8 3 C atoms8 H atoms H2OH2OC3H8C3H8

Matter Compounds 7 Smith. General Organic & Biolocial Chemistry 2nd Ed. Compounds can be drawn many ways: Different elements are represented by different colors:

Matter Depicting Compounds 8 CH 4 methane Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

Atoms Subatomic Particles 9 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E All matter is composed of the same basic building blocks called atoms. Atoms are composed of three subatomic particles:

Atoms Subatomic Particles 10 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

Atoms Subatomic Particles 11 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Opposite charges attract while like charges repel each other. Protons and electrons attract each other, but two electrons repel each other.

Atoms Subatomic Particles 12 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E From the periodic table: 3 Li Atomic number (Z) is the number of protons in the nucleus. Every atom of a given element has the same number of protons in the nucleus. Different elements have different atomic numbers. A neutral atom has no net overall charge, so Z = number of protons = number of electrons

Atoms Subatomic Particles 13 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Isotopes are atoms of the same element that have a different number of neutrons Cl Mass number (A) Atomic number (Z) the number of protons (Z) + the number of neutrons Mass number (A) = # of protons = 17 # of electrons = 17 # of neutrons = 35 – 17 = 18

Atoms Atomic Weight 14 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E 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 atomic number element symbol atomic weight (amu)

Atoms Determine the Atomic Weight of an Element 15 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Example Step [1] What is the atomic weight of chlorine? List each isotope, it’s mass in atomic mass units, and it’s abundance in nature. Mass (amu) Isotopic AbundanceIsotope Cl-35 Cl % = % =

Atoms Determine the Atomic Weight of an Element 16 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Step [2] Multiply the isotopic abundance by the mass of each isotope, and add up the products x x = = amu amu amu = amu Answer 4 sig. figs. The sum is the atomic weight of the element. 4 sig. figs.

17 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Periodic Table Elements

18 Periodic Table Elements

19 Smith. General Organic & Biolocial Chemistry 2nd Ed. 1A2ABB7A8A Alkali Metals Alkaline Earth Metals Transition Metals Lanthanide & Actinide HalogensNobel Gases Very reactive Metals except for H +1 ions React with Oxygen to form compounds that dissolve into alkaline solutions in water Reactive +2 ions Oxygen compounds are strongly alkaline Many are not water soluble Metals Form ions with several different charges (oxidation states) Tend to form +2 and +3 ions Lanthanides 58 – 71 Actinides 90 – 103 Actinides are radioactive Reactive Form diatomic molecules in elemental state -1 ions Salts with alkali metals Inert Heavier elements have limited reactivity Do not form ions Monoatomic gases Periodic Table Groups

20 Smith. General Organic & Biolocial Chemistry 2nd Ed. Periodic Table Metals, Nonmetals, Metalloids

Periodic Table Metals, Nonmetals, Metalloids 21 Smith. General Organic & Biolocial Chemistry 2nd Ed. MetalsNonmetalsMetalloids Metallic luster, malleable, ductile, hardness variable Conduct heat and electricity Solids at room temperature with the exception of Hg Chemical reactivity varies greatly: Au, Pt unreactive while Na, K very reactive Brittle, dull Insulators, non- conductors of electricity and heat Chemical reactivity varies Exist mostly as compounds rather then pure elements Many are gases, some are solids at room temp, only Br 2 is a liquid. Properties intermediate between metals and nonmetals Metallic shine but brittle Semiconductors: conduct electricity but not as well as metals: examples are silicon and germanium

Atoms Carbon 22 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Carbon’s ability to join with itself and other elements gives it a versatility not seen with any other element in the periodic table. Elemental forms of carbon include the following carbon-only structures: diamondgraphitebuckminsterfullerene

Atoms Electron Configurations & Orbitals 23 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

Atoms Electron Configurations & Orbitals 24 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

Atoms Electron Configurations & Orbitals 25

Atoms Valence Electrons 26 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E The valence shell is the outermost shell (the highest value of n). Be 1s22s21s22s2 Cl 1s22s22p63s23p51s22s22p63s23p5 valence shell: n = 2 # of valence electrons = 2 valence shell: n = 3 # of valence electrons = 7 The electrons in the valence shell are called valence electrons. The chemical properties of an element depend on the number of electrons in the valence shell.

Atoms Valence Electrons 27 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E 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.

Atoms Valence Electrons 28 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Group number: Period 1: Period 2: Period 3: 1A2A3A4A5A 6A 7A8A Li 2s 1 Be 2s 2 B2s22p1B2s22p1 C2s22p2C2s22p2 N2s22p3N2s22p3 O2s22p4O2s22p4 F2s22p5F2s22p5 Ne 2s 2 2p 6 Na 3s 1 Mg 3s 2 Al 3s 2 3p 1 Si 3s 2 3p 2 P3s23p3P3s23p3 S3s23p4S3s23p4 Cl 3s 2 3p 5 Ar 3s 2 3p 6 H1s1H1s1 He 1s 2

Atoms Valence Electrons 29 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E 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 > 4 valence electrons, the dots are paired. Element: # of Valence electrons: Electron-dot symbol: H 1 C 4 O 6 Cl 7 HCO

Atoms Periodic Trends 30 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E The size of atoms increases down a column, as the valence e − are farther from the nucleus. The size of atoms decreases across a row, as the number of protons in the nucleus increases, pulling the valence electrons in closer. Increases Decreases

Atoms Periodic Trends 31 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Decreases The ionization energy is the energy needed to remove an electron from a neutral atom. Na + energyNa + + e – 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.