CHAPTER 2 Atoms and the Periodic Table

Transcription

1 CHAPTER 2 and the Periodic Table General, Organic, & Biological Chemistry Janice Gorzynski Smith CHAPTER 2: & the Periodic Table 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 Smith. General Organic & Biolocial Chemistry 2nd Ed. 2

2 Matter Definition 3 Matter Elements 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 = carbon gold sulfur Smith. General Organic & Biolocial Chemistry 2nd Ed. 4

3 Matter Definition 5 Matter Compounds Compound: a pure substance formed by chemically combining two or more elements together. A chemical formula consists of: Element symbols to show the identity of the elements forming a compound. Subscripts to show the ratio of atoms in the compound. H 2 O C 3 H 8 2 H atoms 1 O atom 3 C atoms 8 H atoms Smith. General Organic & Biolocial Chemistry 2nd Ed. 6

4 Matter Compounds Compounds can be drawn many ways: Different elements are represented by different colors: Smith. General Organic & Biolocial Chemistry 2nd Ed. 7 Matter Depicting Compounds CH 4 methane H H C H H 8

5 Subatomic Particles All matter is composed of the same basic building blocks called atoms. are composed of three subatomic particles: 9 Subatomic Particles 10

6 Subatomic Particles Opposite charges attract while like charges repel each other. Protons and electrons attract each other, but two electrons repel each other. 11 Subatomic Particles 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 12

7 Subatomic Particles Isotopes are atoms of the same element that have a different number of neutrons. Mass number (A) = Mass number (A) Atomic number (Z) Cl # of protons = 17 # of electrons = 17 the number of protons (Z) + the number of neutrons # of neutrons = = 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 atomic number element symbol atomic weight (amu) 14

8 Determine the Atomic Weight of an Element 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. Isotope Cl-35 Cl-37 Mass (amu) Isotopic Abundance 75.78% = % = Determine the Atomic Weight of an Element Step [2] Multiply the isotopic abundance by the mass of each isotope, and add up the products. The sum is the atomic weight of the element x x sig. figs. = = amu amu amu = amu Answer 4 sig. figs. 16

9 Periodic Table Elements 17 Periodic Table Elements 18

10 Periodic Table Groups 1A 2A B B 7A 8A Alkali Metals Alkaline Earth Metals Transition Metals Lanthanide & Actinide Halogens Nobel 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 Actinides 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 Smith. General Organic & Biolocial Chemistry 2nd Ed. 19 Periodic Table Metals, Nonmetals, Metalloids Smith. General Organic & Biolocial Chemistry 2nd Ed. 20

11 Periodic Table Metals, Nonmetals, Metalloids Metals Nonmetals Metalloids 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, nonconductors 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 Smith. General Organic & Biolocial Chemistry 2nd Ed. 21 Carbon 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: diamond graphite buckminsterfullerene 22

12 Electron Configurations & Orbitals 23 Electron Configurations & Orbitals 24

13 Electron Configurations & Orbitals 25 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 1s 2 2s 2 Cl 1s 2 2s 2 2p 6 3s 2 3p 5 valence shell: n = 2 # of valence electrons = 2 valence shell: n = 3 # of valence electrons = 7 26

14 Valence Electrons 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. 27 Valence Electrons Group number: 1A 2A 3A 4A 5A 6A 7A 8A Period 1: H 1s 1 He 1s 2 Period 2: Li 2s 1 Be 2s 2 B C 2s 2 2p 1 2s 2 2p 2 N 2s 2 2p 3 O F Ne 2s 2 2p 4 2s 2 2p 5 2s 2 2p 6 Period 3: Na 3s 1 Mg Al 3s 2 3s 2 3p 1 Si 3s 2 3p 2 P 3s 2 3p 3 S Cl 3s 2 3p 4 3s 2 3p 5 Ar 3s 2 3p 6 28

15 Valence Electrons 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: H C O Cl # of Valence electrons: Electron-dot symbol: H C O Cl 29 Periodic Trends Increases The size of atoms increases down a column, as the valence e! are farther from the nucleus. Decreases The size of atoms decreases across a row, as the number of protons in the nucleus increases, pulling the valence electrons in closer. 30

16 Periodic Trends The ionization energy is the energy needed to remove an electron from a neutral atom. Na + energy Na + + e Increases Decreases Ionization energies decrease down a column as the valence e! get farther away from the positively charged nucleus. Ionization energies increase across a row as the number of protons in the nucleus increases. 31