Atoms, Molecules, and Ions Chapter 2 1

8 X 2 Y 16 X8 Y + 2

2 Dalton’s Atomic Theory ( read pages ) 3

The Structure of the Atom Dalton’s atomic theory -atom, the basic unit of element However, atom has subatomic particles -Electrons, neutrons, protons Electrons -negative charge -negligible mass 4

The Structure of the Atom (cont.) Atom is neutral Nucleus-a dense central core of the atom Protons -positive charge -mass is 1840 times the mass of electron Neutrons -electrically neutral - Mass almost the same as proton 5

6 1.atoms positive charge is concentrated in the nucleus 2.proton (p) has opposite (+) charge of electron (-) 3.mass of p is 1840 x mass of e - (1.67 x g)  particle velocity ~ 1.4 x 10 7 m/s (~5% speed of light) (1908 Nobel Prize in Chemistry) Rutherford’s Experiment

atomic radius ~ 100 pm = 1 x m nuclear radius ~ 5 x pm = 5 x m Rutherford’s Model of the Atom “If the atom is the Houston Astrodome, then the nucleus is a marble on the 50-yard line.”

Surrounding the nucleus is a diffuse region of negative charge populated by: -electrons - negatively charged particles -mass p ≈ mass n ≈ 1840 x mass e - Selected Properties of the Subatomic Particles NameChargeMass(amu)Mass (grams) Electrons (e) x x Protons (p) X Neutrons (n) x

mass p = mass n = 1840 x mass e - 9

10 Radioactivity is spontaneous emission of particles and /or radiation

Atomic Number, Mass Number, and Isotopes Atomic number (Z) = number of protons in a neutral atom #protons = # of electrons (in a neutral atom) Mass number (A) = number of protons (Z) + number of neutrons Number of neutrons = A-Z 11

Known as U-235 and U-238 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), one proton in all 0, 1, and 2 neutrons in the isotopes 3 1 U U Mass Number Atomic Number Element Symbol Atomic Number, Mass Number, and Isotopes

Isotopes - atoms of the same element having different masses. –contain same number of protons –contain different numbers of neutrons Isotopes of Hydrogen Hydrogen (Hydrogen-1) Deuterium (Hydrogen-2) Tritium (Hydrogen-3) 13

Problems 1.Write nuclear symbols for three isotopes of oxygen (atomic no. = 8) in which there are 8, 9, and 10 neutrons, respectively 2.One of the most harmful species in nuclear fallout is radioactive isotope of strontium, has a mass number of 90 and atomic number of 38. Write the nuclear symbol for Sr. How many protons and neutrons in the nucleus? How many electrons? 3.How many protons, neutrons, and electrons in C-14 4.Write the nuclear symbol for an atom that contains 32 protons and 38 neutrons (Use the Periodic Table to find the symbol of the element) 14

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Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal 16

Table 2-2 p58

Molecules A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces (also called chemical bonds) Atoms of the same element or different elements in a fixed ratio. When it is of the same element, it is a pure element, for e.g.., 2 H atoms make one molecule of H 2. Only the six noble gases exist as monoatomic in nature. Others diatomic, polyatomic or ionic in nature. 18

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20 Ions An ion is 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

21 A monoatomic ion contains only one atom: ↑ Atoms with 1,2, and 3 electrons lost or gained. A polyatomic ion contains more than one atom: Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- OH -, CN -, NH 4 +, NO 3 - (a)What does S 8 and 8S signify? (b)Protons and electrons in (a) P 3- and (b) Ti 4+

Figure 2-21 p65

Table 2-5 p65

24 Formulas and Models

25 A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance. An 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

Example Write the molecular formula of methanol. There are four H atoms, one C atom, and one O atom. Therefore, the molecular formula is CH 4 O. However, the standard way of writing the molecular formula for methanol is CH 3 OH because it shows how the atoms are joined in the molecule. 26

2.3 Write the empirical formulas for the following molecules: (a)acetylene (C 2 H 2 ), which is used in welding torches (b)glucose (C 6 H 12 O 6 ), a substance known as blood sugar (c)nitrous oxide (N 2 O), a gas that is used as an anesthetic gas (“laughing gas”) and as an aerosol propellant for whipped creams. 27

2.3 Solution (a)There are two carbon atoms and two hydrogen atoms in acetylene. Dividing the subscripts by 2, we obtain the empirical formula CH. (b) In glucose there are 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. Dividing the subscripts by 6, we obtain the empirical formula CH 2 O. Note that if we had divided the subscripts by 3, we would have obtained the formula C 2 H 4 O 2. Although the ratio of carbon to hydrogen to oxygen atoms in C 2 H 4 O 2 is the same as that in C 6 H 12 O 6 (1:2:1), C 2 H 4 O 2 is not the simplest formula because its subscripts are not in the smallest whole-number ratio. 28

2.3 (c) Because the subscripts in N 2 O are already the smallest possible whole numbers, the empirical formula for nitrous oxide is the same as its molecular formula. 29

ionic compounds consist of a combination of cations and an anions the formula is always the same as the empirical formula the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl 30

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32 Formulas of Ionic Compounds Al 2 O 3 2 x +3 = +63 x -2 = -6 Al 3+ O 2- CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br - Na 2 CO 3 2 x +1 = +21 x -2 = -2 Na + CO 3 2-

Most ionic compounds contain metal and nonmetal atoms; for example, NaCl. Chemical Substances; Formulas and Names Ionic compounds You name an ionic compound by giving the name of the cation followed by the name of the anion. A monatomic ion is an ion formed from a single atom.

Most of the main group metals form cations with the charge equal to their group number. Chemical Substances; Formulas and Names Rules for predicting charges on monatomic ions The charge on a monatomic anion for a nonmetal equals the group number minus 8. Most transition elements form more than one ion, each with a different charge.

Monatomic cations are named after the element – if there is only one such ion. For example, Al 3+ is called the aluminum ion. Chemical Substances; Formulas and Names Rules for naming monatomic ions If there is more than one cation of an element, a Roman numeral in parentheses denoting the charge on the ion is used. This often occurs with transition elements. i.e. Fe 2+ = Iron(II); Fe 3+ = Iron(III) The names of the monatomic anions use the stem name of the element followed by the suffix – ide. For example, Br - is called the bromide ion.

A polyatomic ion is an ion consisting of two or more atoms chemically bonded together and carrying a net electric charge. Chemical Substances; Formulas and Names Polyatomic ions OH - hydroxide

37 Chemical Nomenclature Ionic Compounds –Often a metal + nonmetal –Anion (nonmetal), add “-ide” to element name BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate

38 Transition metal ionic compounds –indicate charge on metal with Roman numerals FeCl 2 2 Cl - -2 so Fe is +2iron(II) chloride FeCl 3 3 Cl - -3 so Fe is +3iron(III) chloride Cr 2 S 3 3 S so Cr is +3 (6/2)chromium(III) sulfide

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Molecular compounds nonmetals or nonmetals + metalloids common names H 2 O, NH 3, CH 4, C 60 element further left in periodic table is 1 st element closest to bottom of group is 1 st if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom last element ends in ide

42 HIhydrogen iodide NF 3 nitrogen trifluoride SO 2 sulfur dioxide N 2 Cl 4 dinitrogen tetrachloride NO 2 nitrogen dioxide N2ON2Odinitrogen monoxide Molecular Compounds

2.7 Name the following molecular compounds: (a)SiCl 4 (b)P 4 O 10 43

2.7 Strategy We refer to Table 2.4 for prefixes. In (a) there is only one Si atom so we do not use the prefix “mono.” Solution (a)Because there are four chlorine atoms present, the compound is silicon tetrachloride. (b)There are four phosphorus atoms and ten oxygen atoms present, so the compound is tetraphosphorus decoxide. Note that the “a” is omitted in “deca.” 44

45 An acid can be defined as a substance that yields hydrogen ions (H + ) when dissolved in water. For example: HCl gas and HCl in water Pure substance, hydrogen chloride Dissolved in water (H 3 O + and Cl − ), hydrochloric acid

46 An oxoacid is an acid that contains hydrogen, oxygen, and another element. HNO 3 nitric acid H 2 CO 3 carbonic acid H 3 PO 4 phosphoric acid

Table 2-7 p70

Table 2-8 p70

Figure 2-24 p70

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52 A base can be defined as a substance that yields hydroxide ions (OH - ) when dissolved in water. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH) 2 barium hydroxide

Hydrates are compounds that have a specific number of water molecules attached to them. BaCl 2 2H 2 O LiClH 2 O MgSO 4 7H 2 O Sr(NO 3 ) 2 4H 2 O barium chloride dihydrate lithium chloride monohydrate magnesium sulfate heptahydrate strontium nitrate tetrahydrate CuSO 4 5H2O CuSO4 53

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Homework Problems, Ch.2 11,12,13,14,15,21, 27, 31, 49,50,51,52,53,55,56,57,58,64,65,71,72, 73,74,82,2.84,85,86 55