1. Atoms, Molecules and Ions Chapter 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal Figure 2.13

3. Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei X A Z H 1 1 H (D) 2 1 H (T) 3 1 U 235 92 U 238 92 Mass Number Atomic Number Element Symbol Fissionable

4. The Three Isotopes of Hydrogen 99.9885%0.0115%Trace%

5. How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ? 6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons Do You Understand Isotopes?

6. Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal Figure 2.16

7. Molecule - an aggregate of two or more atoms in a definite arrangement held together by chemical bonds H2H2 H2OH2ONH 3 CH 4 Diatomic molecule - contains only two atoms H 2, N 2, O 2, Br 2, HCl, CO Polyatomic molecule - contains more than two atoms O 3, H 2 O, NH 3, CH 4

8. These seven elements occur naturally as molecules containing two atoms. Diatomic Molecules Fig 2.19

9. Molecular formula - shows the exact number of atoms of each element in the smallest unit of a substance Empirical formula - shows the simplest whole-number ratio of the atoms in a substance H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH 2

10. Analogous to Figure 2.21

11. Ion - an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons

12. Ions Fig 2.22 When atoms lose or gain electrons, they become ions: –Cations are positive - formed by elements on the left side of the periodic chart. –Anions are negative - formed by elements on the right side of the periodic chart.

13. Ionic Bonds Ionic compounds (such as NaCl) - formed between metals and nonmetals. No molecules exist in an ionic compound! Formula always the same as empirical formula. Fig 2.23

14. Monatomic ion - contains only one atom Polyatomic ion - contains more than one atom Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- OH -, CN -, NH 4 +, NO 3 -

15. 13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons Do You Understand Ions? How many protons and electrons are in Al 27 13 ? 3+3+ How many protons and electrons are in Se 78 34 2- ?

16. Charges on Some Common Monatomic Ions Fig 2.22

17. Formulas of Ionic Compounds Al 2 O 3 2 x +3 = +63 x -2 = -6 Al 3+ O2‒O2‒ CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br ‒ Na 2 S 1 x +2 = +21 x -2 = -2 Na + S2‒S2‒