1. Chapter 2 Atoms, Molecules, and Ions Lecture Presentation © 2012 Pearson Education, Inc.

2. Dalton's Postulates Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

3. © 2012 Pearson Education, Inc. Dalton's Postulates Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

4. © 2012 Pearson Education, Inc. Subatomic Particles Protons and electrons are the only particles that have a charge. Protons and neutrons have essentially the same mass. The mass of an electron is so small we ignore it.

5. © 2012 Pearson Education, Inc. Symbols of Elements Elements are symbolized by one or two letters.

6. © 2012 Pearson Education, Inc. Symbols of Elements All atoms of the same element have the same number of protons, which is called the atomic number, Z.

7. © 2012 Pearson Education, Inc. Symbols of Elements The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

8. © 2012 Pearson Education, Inc. Isotopes Isotopes are atoms of the same element with different masses. Isotopes have different numbers of neutrons.

9. Key Points The elements of The Periodic Table are classified into three groups – metals, nonmetals, and metalloids Elements in a group have similar chemical properties Elements in a in a period have different chemical properties

10. Figure 2.11 Metals, metalloids, and nonmetals. Chromium Copper Cadmium Lead Bismuth Boron Silicon Arsenic Antimony Tellurium Carbon (graphite) Sulfur Chlorine Bromine Iodine

11. The modern periodic table. Alkali metals Alkaline earth metals Halogens Noble Gases Transition Metals

12. Figure 2.10 The modern periodic table. +1 +2 +3-3-2 0 NC

13. © 2012 Pearson Education, Inc. Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.

14. © 2012 Pearson Education, Inc. Diatomic Molecules These seven elements occur naturally as molecules containing two atoms: – Hydrogen – Nitrogen – Oxygen – Fluorine – Chlorine – Bromine – Iodine

15. Chemical Formulas Molecular Formula – It only shows the exact number of atoms of each element in the smallest possible units of a substance – Ex. H 2 O, O 2, N 2 Empirical Formula – Tells us what elements are present and the simplest whole number ratio of their atoms – Not necessarily the actual number of atoms in a given molecule. N 2 H 4 molecular formula NH 2 empirical formula

16. © 2012 Pearson Education, Inc. Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.

17. © 2012 Pearson Education, Inc. Chemical Formulas Molecular (covalent or binary) compounds are composed of molecules and almost always contain only nonmetals.

18. © 2012 Pearson Education, Inc. Ions When atoms lose or gain electrons, they become ions. – Cations are positive and are formed by elements on the left side of the periodic chart (donate electrons to non- metals) – Anions are negative and are formed by elements on the right side of the periodic chart (gain electrons from metals)

19. 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 2.5

20. © 2012 Pearson Education, Inc. Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: – The charge on the cation becomes the subscript on the anion. – The charge on the anion becomes the subscript on the cation. – If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.

21. The sum of the charges on the cation and the anion have to add up to zero, thus the compound is electronically neutral – Ex Al 2 O 3 Predicting Ionic Charge – The number of electrons an atom loses or gains is related to its position on the periodic table.

22. Naming Ionic Compounds cont.. Certain Metals especially transition metals can form more than one type of cation We use the Stock System to name them – Mn 2+ MnO (manganese (II) oxide) – Mn 3+ Mn2O 3 (manganese (III) oxide) – Mn 4+ MnO 2 (manganese (IV) oxide)

23. Naming Ionic Compounds cont.. Binary compounds: made from just 2 elements – Cation (electron donating number fixed) is named first and the name of the element stays the same – Cation (electron donating more than one) follow the mentioned above rules – Anion (electron accepting) is named second and you add -ide Ex. Oxygen turns to Oxide Ex Nitrogen turns to Nitride

24. Sample Problem 2.5 Naming Binary Ionic Compounds PROBLEM: Name the ionic compound formed from the following pairs of elements: (a) magnesium and nitrogen SOLUTION: (b) iodine and cadmium (c) strontium and fluorine(d) sulfur and cesium (a) magnesium nitride (b) cadmium iodide (c) strontium fluoride (d) cesium sulfide

25. Sample Problem 2.6 Determining Formulas of Binary Ionic Compounds PROBLEM: Write empirical formulas for the compounds named in Sample Problem 2.5. SOLUTION: Mg 2+ and N 3- ; three Mg 2+ (6+) and two N 3- (6-); Mg 3 N 2 Cd 2+ and I - ; one Cd 2+ (2+) and two I - (2-); CdI 2 Sr 2+ and F - ; one Sr 2+ (2+) and two F - (2-); SrF 2 Cs + and S 2 - ; two Cs + (2+) and one S 2 - (2-); Cs 2 S (a) magnesium nitride (b) cadmium iodide (c) strontium fluoride (d) cesium sulfide

26. Naming Ionic Compounds cont.. Ternary Compounds: made up three elements – If cation (electron donating) has a fixed number of electrons to give the name will stay the same and it is named first – If the cation (electron donating) different number of electrons to give the name will stay the same but you will mention the number of electrons (roman numerals) that are being donating and it is still named first – If the anion (electron accepting) 1 element then you will add –ide – If the anion (electron accepting) more than one element refer to table 2.5 page 63, it is mentioned after the cation

27. Sample Problem 2.8Determining Names and Formulas of Ionic Compounds Containing Polyatomic Ions SOLUTION: PROBLEM: Give the systematic names or the formula or the formulas for the names of the following compounds: (a) Fe(ClO 4 ) 2 (b) sodium sulfite (a) ClO 4 - is perchlorate; iron must have a 2+ charge. This is iron(II) perchlorate. (b) The anion sulfite is SO 3 2- therefore you need 2 sodiums per sulfite. The formula is Na 2 SO 3. (c) Hydroxide is OH - and barium is a 2+ ion. When water is included in the formula, we use the term “hydrate” and a prefix which indicates the number of waters. So it is barium hydroxide octahydrate. (c) Ba(OH) 2 8H 2 O

28. Molecular Compounds They are usually composed of nonmetal elements The chemical bond that forms between the elements is called “covalent bond” – Most of them are binary compounds – Named in the same manner as ionic compounds

29. Naming Molecular Compounds The first name the element that is first in the formula, its name does not change The second element in the formula is named second and –ide is added – HCl (hydrogen chloride) – HBr (hydrogen bromide)

30. Nomenclature of Binary Compounds The less electronegative atom is usually listed first. A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however). The ending on the more electronegative element is changed to -ide. – CO 2 : carbon dioxide – CCl 4 : carbon tetrachloride

31. © 2012 Pearson Education, Inc. Nomenclature of Binary Compounds If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one. N 2 O 5 : dinitrogen pentoxide

32. © 2012 Pearson Education, Inc. Patterns in Oxyanion Nomenclature When there are two oxyanions involving the same element: – The one with fewer oxygens ends in -ite. – The one with more oxygens ends in -ate. NO 2 − : nitrite ; SO 3 2− : sulfite NO 3 − : nitrate; SO 4 2− : sulfate

33. Sample Problem 2.11Determining Names and Formulas of Binary Covalent Compounds SOLUTION: PROBLEM:(a) What is the formula of carbon disulfide? (c) Give the name and formula of the compound whose molecules each consist of two N atoms and four O atoms. (b) What is the name of PCl 5 ? (a) Carbon is C, sulfide is sulfur S and di-means 2 - CS 2. (b) P is phosphorous, Cl is chloride, the prefix for 5 is penta-. Phosphorous pentachloride. (c) N is nitrogen and is in a lower group number than O (oxygen). Therefore the formula is N 2 O 4 - dinitrogen tetraoxide.

34. Acids Acid: a substance that yields hydrogen ions (H +, equivalent to a proton) when dissolved in water – Formulas for acids contain one or more hydrogen as well as an anionic group – The name assigned to the compound depends on its physical state Anions whose names end in “ide” form acids with a “hydro” prefix and an “ic” ending – HCl Hydrochloric acid

35. Naming Acids

36. Sample Problem 2.10Determining Names and Formulas of Anions and Acids SOLUTION: PROBLEM: Name the following anions and give the names and formulas of the acids derived from them: (a) Br - (b) I O 3 - (c) CN - (d) SO 4 2- (e) NO 2 - (a) The anion is bromide; the acid is hydrobromic acid, HBr. (b) The anion is iodate; the acid is iodic acid, H I O 3. (c) The anion is cyanide; the acid is hydrocyanic acid, HCN. (d) The anion is sulfate; the acid is sulfuric acid, H 2 SO 4. (e) The anion is nitrite; the acid is nitrous acid, HNO 2.