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

1. CHAPTER 2 Atoms and the Periodic Table General, Organic, & Biological Chemistry Janice GorzynskiSmith

2. CHAPTER 2: Atoms & 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.

3. Matter Definition http://ridenourmhs.wikispaces.com/ESUnit2

4. 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.

5. Matter Definition http://ridenourmhs.wikispaces.com/ESUnit2

6. 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. H2O H2O C3H8 C3H8 2 H atoms 1 O atom 3 C atoms 8 H atoms Smith. General Organic & Biolocial Chemistry 2nd Ed.

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

8. Matter Depicting Compounds CH4 methane Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

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

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

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

12. Atoms Subatomic Particles From the periodic table: Atomic number (Z) is the number of protons in the nucleus. 3 Li • 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 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

13. Atoms Subatomic Particles 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 Cl Atomic number (Z) 17 # of protons = 17 # of electrons = 17 # of neutrons = 35 – 17 = 18 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

14. Atoms 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: atomic number 6 C 12.01 element symbol atomic weight (amu) Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

15. Atoms Determine the Atomic Weight of an Element What is the atomic weight of chlorine? Example List each isotope, it’s mass in atomic mass units, and it’s abundance in nature. Step [1] Mass (amu) Isotope Isotopic Abundance Cl-35 34.97 75.78% = 0.7578 Cl-37 36.97 24.22% = 0.2422 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

16. Atoms 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. 34.97 x 0.7578 26.5003 amu = 36.97 x 0.2422 = 8.9541 amu 35.45amu 35.4544 amu = Answer 4 sig. figs. 4 sig. figs. Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

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

18. Periodic Table Elements

19. Periodic Table Groups Smith. General Organic & Biolocial Chemistry 2nd Ed.

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

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

22. Atoms Carbon Carbon’s ability to join with itself and other elementsgives 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 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

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

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

25. Atoms Electron Configurations & Orbitals http://chemwiki.ucdavis.edu/

26. Atoms 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 1s22s22p63s23p5 1s22s2 valence shell: n = 2 valence shell: n = 3 # of valence electrons = 2 # of valence electrons = 7 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

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

28. Atoms Valence Electrons Group number: 6A 1A 2A 3A 4A 5A 7A 8A 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 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

29. Atoms 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. H Element: O Cl C # of Valence electrons: 1 4 6 7 Electron-dot symbol: H C O Cl Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

30. Atoms Periodic Trends 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. Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

31. Atoms Periodic Trends The ionization energy is the energy needed to remove an electron from a neutral atom. Na + energy Na+ + e– • Ionization energies • decrease down a • column as the • valence e− get • farther away from • the positively charged nucleus. Decreases Increases • Ionization energies increase across a row as the • number of protons in the nucleus increases. Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E