Atoms and Elements

Introductory Chemistry, 3rd EditionNivaldo Tro : Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Introductory Chemistry, 3rd EditionNivaldo Tro Chapter 4 Atoms and Elements 2009, Prentice Hall

Experiencing Atoms : Tro's "Introductory Chemistry", Chapter 4 2 Experiencing Atoms Atoms are incredibly small All of our senses, sense atoms

Experiencing Atoms : Tro's "Introductory Chemistry", Chapter 4 3 Experiencing Atoms There are about 91 elements found in nature. Over 20 have been made in laboratories. Each kind of atom is unique Carbon is not Hydrogen They have different properties Structure, magnetic meaning they can attract and repel other atoms, melting, boiling, electrical, stability, reactivity (attract and repel), etc…

The Divisibility of Matter : Tro's "Introductory Chemistry", Chapter 4 4 The Divisibility of Matter Ultimate particle Upon division, eventually a particle is reached which can no longer be divided. Atoms are 10-11m We detect particles at 10-15m In theory particles 10-35m exist, we don’t have instruments that sensitive “Nothing exists except atoms and empty space; everything else is opinion.” - Democritus 460–370 B.C.

Modern Evidence for Atoms : Modern Evidence for Atoms IBM's Almaden Research Center in San Jose, California, April 1990 Tro's "Introductory Chemistry", Chapter 4 5

Sizes of Atoms : Tro's "Introductory Chemistry", Chapter 4 6 Sizes of Atoms Using compositions of compounds and assumed formulas, Dalton was able to determine the relative masses of the atoms. Dalton based his scale on H = 1 amu. We now base it on C-12 = 12 amu exactly. Unit = atomic mass unit. Amu or dalton. Absolute sizes of atoms: Mass of H atom= 1.67 x 10-24g. Volume of H atom = 2.1 x 10-25cm3.

The Atom Is Divisible : Tro's "Introductory Chemistry", Chapter 4 7 The Atom Is Divisible Work done by J. J. Thomson and others proved that the atom had pieces called electrons. Thomson found that electrons are much smaller than atoms and carry a negative charge. The mass of the electron is 1/1836th the mass of a hydrogen atom. The charge on the electron is the fundamental unit of charge that we call –1 charge unit.

Plum Pudding Atom : Tro's "Introductory Chemistry", Chapter 4 8 Plum Pudding Atom

Rutherford’s Experiment : 9 Rutherford’s Experiment How can you prove something is empty? Put something through it. Use large target atoms. Use very thin sheets of target so they do not absorb “bullet”. Use very small particles as “bullet” with very high energy. But not so small that electrons will effect it. Bullet = alpha particles; target atoms = gold foil a particles have a mass of 4 amu & charge of +2 c.u. Gold has a mass of 197 amu and is very malleable.

Rutherford’s Experiment : Tro's "Introductory Chemistry", Chapter 4 10 Rutherford’s Experiment Lead box Radioactive sample Gold foil Fluorescent screen

Slide 11 : Tro's "Introductory Chemistry", Chapter 4 11

Rutherford’s Interpretation—The Nuclear Model : 12 Rutherford’s Interpretation—The Nuclear Model 1. The atom contains a tiny dense center called the nucleus. The amount of space taken by the nucleus is only about 1/10 trillionth the volume of the atom. 2. The nucleus has essentially the entire mass of the atom. The electrons weigh so little they contribute practically no mass to the atom. 3. The nucleus is positively charged. The amount of positive charge balances the negative charge of the electrons. 4. The electrons are dispersed in the empty space of the atom surrounding the nucleus. Like water droplets in a cloud.

Some Problems : Tro's "Introductory Chemistry", Chapter 4 13 Some Problems How could beryllium have 4 protons stuck together in the nucleus? Shouldn’t they repel each other? If a beryllium atom has 4 protons, then it should weigh 4 amu, but it actually weighs 9.01 amu! Where is the extra mass coming from? Each proton weighs 1 amu. Remember: The electron’s mass is only about 0.00055 amu and Be has only 4 electrons—it can’t account for the extra 5 amu of mass.

There Must Be Something Else There : Tro's "Introductory Chemistry", Chapter 4 14 There Must Be Something Else There To answer these questions, Rutherford proposed that there was another particle in the nucleus—it is called a neutron. Neutrons have no charge and a mass of 1 amu. The masses of the proton and neutron are both approximately 1 amu.

Slide 15 : Tro's "Introductory Chemistry", Chapter 4 15

The Modern Atom : Tro's "Introductory Chemistry", Chapter 4 16 The Modern Atom We know atoms are composed of three main pieces—protons, neutrons, and electrons. The nucleus contains protons and neutrons. The nucleus is only about 10-13 cm in diameter. The electrons move outside the nucleus with an average distance of about 10-8 cm. Therefore, the radius of the atom is about 105 times larger than the radius of the nucleus.

Some Notes on Charges : Tro's "Introductory Chemistry", Chapter 4 17 Some Notes on Charges There are two kinds of charges, called positive and negative. Opposite charges attract. + attracted to –. Like charges repel. + repels +. – repels –. To be neutral, something must have no charge or equal amounts of opposite charges.

The Nature of Electrical Charge : Tro's "Introductory Chemistry", Chapter 4 18 The Nature of Electrical Charge Electrical charge is a fundamental property of protons and electrons. Positively and negatively charged objects attract each other. Like charged objects repel each other. + to +, or  to . When a proton and electron are paired, the result is a neutral charge. Because they have equal amounts of charge.

Practice—An Atom Has 20 Protons. Determine if Each of the Following Statements Is True or False? : Tro's "Introductory Chemistry", Chapter 4 19 Practice—An Atom Has 20 Protons. Determine if Each of the Following Statements Is True or False? If it is a neutral atom, it will have 20 electrons. If it also has 20 neutrons, its mass will be approximately 40 amu. If it has 18 electrons, it will have a net 2 charge. True True False

Elements : 20 Elements Each element has a unique number of protons in its nucleus. All carbon atoms have 6 protons in their nuclei. The number of protons in the nucleus of an atom is called the atomic number. Z is the short-hand designation for the atomic number. Because each element’s atoms have a unique number of protons, each element can be identified by its atomic number. The elements are arranged on the Periodic Table in order of their atomic numbers. Each element has a unique name and symbol. The symbol is either one or two letters One capital letter or one capital letter + one lower case letter.

The Periodic Table of Elements : Tro's "Introductory Chemistry", Chapter 4 21 The Periodic Table of Elements

Review : Tro's "Introductory Chemistry", Chapter 4 22 Review What is the atomic number of boron, B? 5 What is the atomic mass of silicon, Si? 28.09 amu How many protons does a chlorine atom have? 17 How many electrons does a neutral neon atom have? 10 Will an atom with 6 protons, 6 neutrons and 6 electrons be electrically neutral? Yes Will an atom with 27 protons, 32 neutrons, and 27 electrons be electrically neutral? Yes Will an Na atom with 10 electrons be electrically neutral? No

Mendeleev : Tro's "Introductory Chemistry", Chapter 4 23 Mendeleev Ordered elements by atomic mass. Saw a repeating pattern of properties. Periodic law—When the elements are arranged in order of increasing relative mass, certain sets of properties recur periodically? Used pattern to predict properties of undiscovered elements. Where atomic mass order did not fit other properties, he reordered by other properties. Te & I

Periodic Pattern : Tro's "Introductory Chemistry", Chapter 4 24 Periodic Pattern a = acidic oxide, b = basic oxide, a/b = amphoteric oxide m = metal, nm = nonmetal, m/nm = metalloid

Mendeleev's Predictions for Ekasilicon (Germanium) : Tro's "Introductory Chemistry", Chapter 4 25 Mendeleev's Predictions for Ekasilicon (Germanium)

Periodicity : Tro's "Introductory Chemistry", Chapter 4 26 Periodicity = Metal = Metalloid = Nonmetal

Metals : 27 Metals Solids at room temperature, except Hg. Reflective surface. Shiny Conduct heat. Conduct electricity. Malleable. Can be shaped. Ductile. Drawn or pulled into wires. Lose electrons and form cations in reactions. About 75% of the elements are metals. Lower left on the table.

Nonmetals : Tro's "Introductory Chemistry", Chapter 4 28 Nonmetals Found in all 3 states. Poor conductors of heat. Poor conductors of electricity. Solids are brittle. Gain electrons in reactions to become anions. Upper right on the table. Except H.

Metalloids : Tro's "Introductory Chemistry", Chapter 4 29 Metalloids Show some properties of metals and some of nonmetals. Also known as semiconductors. Properties of Silicon: Shiny Conducts electricity Does not conduct heat well Brittle

Practice—Classify Each Element as Metal, Nonmetal, or Metalloid. : Tro's "Introductory Chemistry", Chapter 4 30 Practice—Classify Each Element as Metal, Nonmetal, or Metalloid. Xenon, Xe Tungsten, W Bromine, Br Arsenic, As Cerium, Ce Nonmetal Metal Nonmetal Metalloid Metal

The Modern Periodic Table : Tro's "Introductory Chemistry", Chapter 4 31 The Modern Periodic Table Elements with similar chemical and physical properties are in the same column. Columns are called Groups or Families. Designated by a number and letter at top. Rows are called Periods. Each period shows the pattern of properties repeated in the next period.

The Modern Periodic Table, Continued : Tro's "Introductory Chemistry", Chapter 4 32 The Modern Periodic Table, Continued Main group = representative elements = “A” groups. Transition elements = “B” groups. All metals. Bottom rows = inner transition elements = rare earth elements. Metals Really belong in periods 6 and 7.

Slide 33 : Tro's "Introductory Chemistry", Chapter 4 33 = Halogens = Lanthanides = Actinides

Important Groups—Hydrogen : Tro's "Introductory Chemistry", Chapter 4 34 Important Groups—Hydrogen Nonmetal. Colorless, diatomic gas. Very low melting point and density. Reacts with nonmetals to form molecular compounds. HCl is an acidic gas. H2O is a liquid. Reacts with metals to form hydrides. Metal hydrides react with water to form H2. hydrogen halides dissolve in water to form acids.

Important Groups—Alkali Metals : Tro's "Introductory Chemistry", Chapter 4 35 Important Groups—Alkali Metals Group IA = Alkali metals. Hydrogen is usually placed here, though it doesn’t belong. Soft, low melting points, low density. Flame tests: Li = red, Na = yellow, and K = violet. Very reactive, never found uncombined in nature. Tend to form water soluble compounds that are crystallized from seawater then molten salt electrolyzed. Colorless solutions. React with water to form basic (alkaline) solutions and H2: 2 Na + 2 H2O  2 NaOH + H2 Releases a lot of heat. lithium sodium potassium rubidium cesium

Important Groups—Alkali Earth Metals : Tro's "Introductory Chemistry", Chapter 4 36 Important Groups—Alkali Earth Metals Group IIA = Alkali earth metals. Harder, higher melting, and denser than alkali metals. Mg alloys used as structural materials. Flame tests: Ca = red, Sr = red, and Ba = yellow-green. Reactive, but less than corresponding alkali metal. Form stable, insoluble oxides from which they are normally extracted. Oxides are basic = alkaline earth. Reactivity with water to form H2: Be = none, Mg = steam, Ca, Sr, Ba = cold water. magnesium calcium beryllium strontium barium

Important Groups—Halogens : 37 Important Groups—Halogens Group VIIA = Halogens. Nonmetals. F2 and Cl2 gases, Br2 liquid, and I2 solid. All diatomic. Very reactive. Cl2, and Br2 react slowly with water: Br2 + H2O ® HBr + HOBr React with metals to form ionic compounds. hydrogen halides all acids: HF weak < HCl < HBr < HI. bromine iodine chlorine fluorine

Important Groups—Noble Gases : Tro's "Introductory Chemistry", Chapter 4 38 Important Groups—Noble Gases Group VIIIA = Noble gases. All gases at room temperature. Very low melting and boiling points. Very unreactive, practically inert. Very hard to remove electron from or give an electron to.

Important Groups—Noble Gases : Tro's "Introductory Chemistry", Chapter 4 39 Important Groups—Noble Gases This unreactive and The difficulty to remove and electron from Noble Gases has to do with the number of electrons From a Quantum point of view these elements have all the electrons they need. Which means, all the other atoms do NOT have all the electrons they need…want.

Atom Happiness : Atom Happiness The number of proton determines the physical and chemical properties of an atom When the protons=electrons atoms are electrically neutral But Atom Happiness only comes about when the atom has the same number of Electrons as a noble gas Tro's "Introductory Chemistry", Chapter 4 40

Atom Happiness : Atom Happiness Atoms will not gain and loose protons because protons are at the center of atoms, very far away from outside, in an electrical shroud of negative charge Atoms will gain and loose electrons, which are on the outside surface of atoms When an atom gains or looses an electron the electrical balance is lost But, atoms are happier with a charge Tro's "Introductory Chemistry", Chapter 4 41

Ions : Tro's "Introductory Chemistry", Chapter 4 42 Ions Ions with a positive charge are called cations. More protons than electrons. Form by losing electrons. Ions with a negative charge are called anions. More electrons than protons. Form by gaining electrons. Chemically, ions are much different than the neutral atoms. Because they have a different structure.

Atomic Structures of Ions : Tro's "Introductory Chemistry", Chapter 4 43 Atomic Structures of Ions Nonmetals form anions. For each negative charge, the ion has 1 more electron than the neutral atom. F = 9 p+ and 9 e; F─ = 9 p+ and 10 e. P = 15 p+ and 15 e; P3─ = 15 p+ and 18 e. Anions are named by changing the ending of the name to –ide. fluorine F + 1e  F─ fluoride ion oxygen O + 2e  O2─ oxide ion The charge on an anion can often be determined from the group number on the periodic table. Group 7A  1, Group 6A  2.

Atomic Structures of Ions, Continued : Tro's "Introductory Chemistry", Chapter 4 44 Atomic Structures of Ions, Continued Metals form cations. For each positive charge the ion has 1 less electron than the neutral atom. Na atom = 11 p+ and 11 e; Na+ ion = 11 p+ and 10 e. Ca atom = 20 p+ and 20 e; Ca2+ ion = 20 p+ and 18 e. Cations are named the same as the metal. sodium Na  Na+ + 1e sodium ion calcium Ca  Ca2+ + 2e calcium ion The charge on a cation can often be determined from the group number on the periodic table. Group 1A  1+, Group 2A  2+, (Al, Ga, In)  3+.

Example 4.5—Find the Number of Protons and Electrons in Ca2+. : Example 4.5—Find the Number of Protons and Electrons in Ca2+. For cations, p+ > e−, so the answer is reasonable. Check: Z = 20 = #p+ Solution: ion charge = #p+ − #e− Solution Map: Relationships: Ca2+ # p+, # e-, # n0 Given: Find: ion charge = #p+ − #e− +2 = 20 − #e− ─18 = ─ #e− 18 = #e−

Practice—Fill in the Table. : Tro's "Introductory Chemistry", Chapter 4 46 Practice—Fill in the Table.

Practice—Fill in the Table, Continued. : Tro's "Introductory Chemistry", Chapter 4 47 Practice—Fill in the Table, Continued.

Valence Electrons and Ion Charge : Tro's "Introductory Chemistry", Chapter 4 48 Valence Electrons and Ion Charge The highest energy electrons in an atom are called the valence electrons. Metals form cations by losing their valence electrons to get the same number of electrons as the previous noble gas. Main group metals. Li+ = 2 e = He; Al3+ = 10 e = Ne. Nonmetals form anions by gaining electrons to have the same number of electrons as the next noble gas. Cl = 18 e = Ar; Se2 = 36 e = Kr.

Ion Charge and the Periodic Table : Tro's "Introductory Chemistry", Chapter 4 49 Ion Charge and the Periodic Table The charge on an ion can often be determined from an elements position on the periodic table. Metals are always positive ions, nonmetals are negative ions. For many main group metals, the cation charge = the group number. For nonmetals, the anion charge = the group number – 8.

Slide 50 : Tro's "Introductory Chemistry", Chapter 4 50 Li+ Na+ K+ Rb+ Cs+ Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Al3+ Ga3+ In3+ O2 S2 Se2 Te2 F Cl Br I N3 P3 As3 1A 2A 3A 7A 6A 5A

Structure of the Nucleus : Tro's "Introductory Chemistry", Chapter 4 51 Structure of the Nucleus Soddy discovered that the same element could have atoms with different masses, which he called isotopes. There are two isotopes of chlorine found in nature, one that has a mass of about 35 amu and another that weighs about 37 amu. The observed mass is a weighted average of the weights of all the naturally occurring atoms. The atomic mass of chlorine is 35.45 amu.

Isotopes : Tro's "Introductory Chemistry", Chapter 4 52 Isotopes All isotopes of an element are chemically identical. Undergo the exact same chemical reactions. All isotopes of an element have the same number of protons. Isotopes of an element have different masses. Isotopes of an element have different numbers of neutrons. Isotopes are identified by their mass numbers. Protons + neutrons.

Isotopes, Continued : 53 Atomic Number. Number of protons. Z Mass Number = Protons + Neutrons. Whole number. A Percent natural abundance = Relative amount found in a sample. Isotopes, Continued

Neon : Tro's "Introductory Chemistry", Chapter 4 54 Neon

Isotopes : Tro's "Introductory Chemistry", Chapter 4 55 Isotopes Cl-35 makes up about 75% of chlorine atoms in nature, and Cl-37 makes up the remaining 25%. The average atomic mass of Cl is 35.45 amu. Cl-35 has a mass number = 35, 17 protons and 18 neutrons (35 - 17).

Example 4.8—How Many Protons and Neutrons Are in an Atom of ? : Example 4.8—How Many Protons and Neutrons Are in an Atom of ? For most stable isotopes, n0 > p+. Check: Z = 24 = # p+ Solution: mass number = # p+ + # n0 Solution Map: Relationships: therefore A = 52, Z = 24 # p+ and # n0 Given: Find: A = Z + # n0 52 = 24 + # n0 28 = # n0

Practice—Complete the Following Table. : Tro's "Introductory Chemistry", Chapter 4 57 Practice—Complete the Following Table.

Practice—Complete the Following Table, Continued. : Tro's "Introductory Chemistry", Chapter 4 58 Practice—Complete the Following Table, Continued.

Mass Number Is Not the Sameas Atomic Mass : Tro's "Introductory Chemistry", Chapter 4 59 Mass Number Is Not the Sameas Atomic Mass The atomic mass is an experimental number determined from all naturally occurring isotopes. The mass number refers to the number of protons + neutrons in one isotope. Natural or man-made.

Example 4.9─Ga-69 with Mass 68.9256 Amu and Abundance of 60.11% and Ga-71 with Mass 70.9247 Amu and Abundance of 39.89%. Calculate the Atomic Mass of Gallium. : Example 4.9─Ga-69 with Mass 68.9256 Amu and Abundance of 60.11% and Ga-71 with Mass 70.9247 Amu and Abundance of 39.89%. Calculate the Atomic Mass of Gallium. The average is between the two masses, closer to the major isotope. Check: Solution: Solution Map: Relationships: Ga-69 = 60.11%, 68.9256 amu Cu-71 = 39.89%, 70.9247 amu atomic mass, amu Given: Find:

Practice—If Copper Is 69.17% Cu-63 with a Mass of 62.9396 Amu and the Rest Cu-65 with a Mass of 64.9278 Amu, Find Copper’s Atomic Mass. : Tro's "Introductory Chemistry", Chapter 4 61 Practice—If Copper Is 69.17% Cu-63 with a Mass of 62.9396 Amu and the Rest Cu-65 with a Mass of 64.9278 Amu, Find Copper’s Atomic Mass.

Practice—If Copper Is 69.17% Cu-63 with a Mass of 62.9396 Amu and the Rest Cu-65 with a Mass of 64.9278 Amu, Find Copper’s Atomic Mass, Continued. : Practice—If Copper Is 69.17% Cu-63 with a Mass of 62.9396 Amu and the Rest Cu-65 with a Mass of 64.9278 Amu, Find Copper’s Atomic Mass, Continued. The average is between the two masses, closer to the major isotope. Check: Solution: Solution Map: Relationships: Cu-63 = 69.17%, 62.9396 amu Cu-65 = 100-69.17%, 64.9278 amu atomic mass, amu Given: Find: