Chemistry 101 - Chapter 2
Magnesium has three isotopes with mass numbers 24, 25, and 26. a) Write the complete chemical symbol (superscript and subscript) for each. b) How many neutrons are in an atom of each isotope?
(a) 24/12Mg; 25/12 Mg; 26/12 Mg (b) Mg 24 = 24 - 12 = 12 Neutrons, 12 Protons and 12 Electrons Mg 25 = 25 - 12 = 13 Neutrons, 12 Protons, 12 Electrons Mg 26 = 26 - 12 = 14 Neutrons, 12 Protons, 12 Electrons
Which of the following oxyanions is incorrectly named? a) ClO2(-) Chlorate b) IO4(-) Periodate c) SO3(2-) Sulfite d) IO3(-) Iodate e) NO2(-) Nitrite
(a) and (d)
Which of the following is an implication of Thomson's observation that the type of metal used to make the cathode does not matter? a) The cathode rays do not originate in the cathode. b) The particles that make up cathode rays must be present in all metals.
(b)
Which of the following acids are incorrectly named? For those that are, provide a correct name or formula a) Hydrofluoric Acid, HF b) Nitrous Acid, HNO3 c) Perbromic Acid, HBrO4 d) Iodic Acid, HI e) Selenic Acid, H2SeO4
(b) should be Nitric Acid
Which of the following ionic compounds is incorrectly named? a) Zn(NO3)2, zinc nitrate b) TeCl4, Tellurium (IV) Chloride c) Fe2O3, Diiron Oxide d) BaO, Barium Oxide e) Mn3(PO4)2, manganese(II)Phosphate
(b), (c) and (e)
Angstrom
(Å) = 100 pm or 1x10^-10 m Used for the diameter of an atom Ex: Chlorine has a diameter of 200 pm or 2.0 Å
Atomic Mass Unit (amu)
1 amu = 1.66 x 10^-24 g
The diameter of a US dime is 17.9 mm, and the diameter of a silver atom is 2.88 Å. How many silver atoms could be arranged side by side across the diameter of a dime?
1 Å = 1x10^-10 m 17.9 mm x (1 m/1000 mm) x (1 Å/1x10^-10 m) =1.79 x 10^8 Å (1.79x10^8 Å)/ (2.88 Å) = 6.22 x 10^7 silver atoms
Two isotopes of Boron are found in nature: 10-B has a mass of 10.01 amu, and 11-B has a mass of 11.01 amu. Use the atomic weight of Boron found (10.81 amu) to determine which isotope is more abundant.
10.81 = (10.01)(x) + (11.01)(y) x = 0.20 or 20% y = 0.80 or 80% I just tried plugging in random percents, 50/50 didn't work, etc.
What is the approximate diameter of the nucleus in units of pm?
10^-4 Å turns into: 10^-2 pm
Give the complete chemical symbol for the atom that contains 82 protons, 82 electrons and 126 neutrons
126 + 82 = 208 Answer: Lead, Pb has a mass number of ~208 and a proton # of 82
If an Atom has 15 protons, how many electrons does it have? Where fo the protons reside in an atom?
15 electrons In the atomic nucleus
Three isotopes of silicon occur in nature: 28-Si (92.23%), atomic mass 27.97693 amu; 29-Si (4.68%), atomic mass 28.97649 amu: and 30-Si (3.09%), atomic mass 29.97377 amu. Calculate the atomic weight of silicon
= (0.9223 x 27.92693) + (0.0468 x 28.97649) + (0.0309 x 29.97377) = 28.0854 amu
Naturally occurring chlorine is 75.78% 35-Cl (atomic mass 34.969 amu) and 24.22% 37-Cl (atomic mass 36.966). Calculate the atomic weight of Chlorine
= (34.969 amu) x 0.7578) + (36.966 x 0.2422 amu) = 35.45 amu
Which subatomic particle - proton, neutron or electron - is equivalent to a β ray? β rays are deflected to a greater extent than α rays because (a) they are lighter, or (b) they are more highly charged
A beta ray is equivalent to an electron. An Alpha ray is less greatly deflected because they are more highly charged
Molecular Formulas
A chemical formula that indicates the actual number of atoms of each element in one molecule of a substance
Empirical Formulas
A chemical formula that shows the kinds of atoms and their relative numbers in a substance in the smallest possible whole-number ratios.
Ionic Compound
A compound composed of cations and anions Generally, ionic compounds are combinations of metals and nonmetals
Molecular Compound
A compound that consists of molecules
Structural Formula
A formula that shows the number and kinds of atoms as well as the arrangement in the molecule
Electrons
A negatively charged subatomic particle found outside of the atomic nucleus
Chemical Formula
A notation that uses chemical symbols with numerical subscripts to convey the relative proportions of atoms of the different elements in a substance
Cation
A positively charged ion *metal atoms tend to lose electrons (forms cations)
If no magnetic field were applied, would you expect the electron beam to be deflected upward or downward by the electric field?
Downward, away from the upper negative plate and towards the positive plate (attraction)
Ion
Electrically charged atom or group of atoms (polyatomic ions); ions can be positively or negatively charged depending on whether electrons are gained or lost
Neutrons
Electrically neutral subatomic particle Approximately the same mass as the Proton
Which of these atoms has the largest number of Neutrons? a) 148 Eu b) 157 Dy c) 149 Nd d) 162 Ho e) 159 Gd
Eu 148 - 63 = 85 Dy 157 - 66 = 91 Nd 149 - 60 = 89 Ho 162 - 67 = 95 Gd 159 - 64 = 95 Answer: d and e
Nuclear Model
Model of the atom with a very small and extremely dense nucleus containing most of the mass (protons and neutrons) and with electrons in the space around the nucleus
Which of these compounds would you expect to be ionic: N2O, Na2O, CaCl2, SF4
Na2O and CaCl2
Beta Particles
Negatively charged (-1)
Is it possible to pick out a unique cluster of atoms that can be thought of as a sodium chloride molecule?
No it is not, ionic solids like NaCl do not contain discrete molecules
Are the masses of the oil drops changed significantly when electrons accumulate on them?
No, the mass of electrons are too small to make a significant change
Subatomic Particles
Particles such as Protons, Neutrons and Electrons - make up an atom
Which of the following is an incorrect representation for a neutral atom?
Per the Periodic Table - Answer is Cu because the mass number is 29, not 30
What is the charge on the particles that form the beam? Will they be attracted to or repelled from the positively charged gold nuclei?
Positive, they were repelled by the positively charged gold nuclei
Alpha Particles
Positively charged (+2)
Protons
Positively charged subatomic particles
How many protons, neutrons, and electrons does the 79-Se (2-) ion possess?
Se = 79 - 34 = 45 Neutrons 45 N, 34 P, 36 E
Atomic Nucleus
Small, dense, positively charged portion of the atom Contains both Protons and Neutrons
Atoms
Smallest representative particle of an element; building blocks of matter
Radioactivity
Spontaneous emission of radiation; the disintegration of an unstable atomic nucleus with accompanying emission of radiation Three types: Alpha (α), Beta (β) and Gamma (γ)
Cathode Rays
Streams of electrons that are produced when a high voltage is applied to electrodes in an evacuated tube Electrons traveled from the negative electrode to the positive
To how many significant figures would you need to express the mass of an oxygen-16 atom in amu to notice the change in mass that occurs when it gains an electron?
The mass of an O atom is 2.6560 x 10^-23 g The mass of an an electron is 5.5x10^-4 amu which means that we would need 4 sig figs past the decimal, and 2 before the decimal = total of 6 sig figs
Binary Naming System
The name of the element further to the left of the periodic table (closes to meetals) is usually written first. An exception occurs when the compound contains oxygen and chlorine, bromine, or iodine (any halogen except Flourine) - in which case the oxygen is written last If both elements are in the same group, the one closer to the bottom is named FIRST The name of the second element is given an "-ide" ending Greek prefixes (mono, etc) indicate the number of atoms of each element
Atomic Number
The number of protons in an atom
Chemical Nomenclature
The rules used in naming substances Cations = metal ions have the same name as the metal If a metal can form cations with different charges, the positive charge is indicated by a roman numeral in parentheses following the name of the metal: Fe2+ Iron(II) ion Fe3+ Iron(III) ion Cu+ Copper(I) ion Cu2+ Copper(II) ion *Normally these are transition metals Cations formed from molecules composed of nonmetal atoms have names that end in -ium NH4+ (ammonium ion) H3O+ (hydronium ion) Anions = The names of monatomic anions formed by replacing the ending of the name of the element with -ide H- hydride ion O2- oxide ion N3- nitride ion Polyatomic anions containing oxygen have names ending in either "-ate" or "-ite"
The Law of Conservation of Mass
The total mass of materials present after a chemical reaction is the same as the total mass before the reaction
Which of the following factors determines the size of an atom?
The volume of space occupied by the electrons of the atom
Tetracarbon Dioxide is an unstable oxide of carbon with the following molecular structure: What are the molecular and empirical formulas of this substance? a) C2O2, CO2 b) C4O, CO c) CO2, CO2 d) C4O2, C2O e) C2O, CO2
There are 2 4 Carbon and 2 Oxygen atoms Answer: D
What information is conveyed by the endings -ide, -ate, and -ite in the name of an anion?
They convey how many oxygen atoms are bound to the nonmetals ide = 1 ite = 2 ate = 3 or 4
What is the empirical formula of the compound formed between W(6+) and O(2-)?
WO3
Perspective Drawings
Wedges and dashed lines depict bonds that are not in the plane of the paper (3-dimensional shape)
If the fluorescent screen were removed from the tube, would cathode rays still be generated? Would you be able to see them?
Yes the Cathode rays would still generate, electrons still exist even if we can't see them via the naked eye.
Anion
a negatively charged ion *Nonmetals tend to gain electrons (form anions)
Oxyanions
a polyatomic anion that contains one or more oxygen atoms NO3(-) nitrate ion NO2(-) nitrite SO4(2-) sulfate ion SO3(2-) sulfite ion
Predict the charge expected for the most stable ion of a) aluminum b) fluorine
a) +3 b) -1
The diameter of a carbon atom is 1.54 Å a) express this diameter in picometers b) How many carbon atoms could be aligned side by side across the width of a pencil that is 0.20 mm wide?
a) 1 Å = 100 pm 1.54 Å x (1x10^-10 m/ 1 Å) x (1 pm/ 1x10^-12 m) = 154 pm b) = 0.20 mm x (1 m/ 1000 mm) x (1 Å/ 1x10^-10) = 2.0x10^6 Å 2.0x10^6 Å/(1.54 Å) = 1.3x10^6 carbon atoms
How many protons, neutrons and electrons are in an atom of a) 197^ Au b) Strontium-90?
a) 197^Au 197 is the mass 197 - 79 = 118 Neutrons Protons 79, 79 Electrons b) Strontium-90 90^Sr 90 - 38 = 52 Neutrons 38 protons,38 electrons
Give the chemical symbol, including superscript indication mass number for a) the ion with 22 protons, 26 neutrons and 19 electrons b) the ion of sulfur that has 16 neutrons and 18 electrons
a) 22 + 26 = 48 is the mass number; 48/22 Ti+3 b) 16 + 16 = 32 is the mass number; 34/16 S -2
Write the empirical formula of the compound formed by a) Al(3+) and Cl(-) ions b) Al(3+) and O(2-) ions c) Mg(2+) and NO3(-)
a) AlCl3 b) Al2O3 c) Mg(NO3)2
Name the ionic compounds a) NH4Br b) Cr2O3 c) Co(NO3)2
a) Ammonium Bromide b) Chromium (III) Oxide c) Cobalt (II) Nitrate
Although it is helpful to know that many ions have the electron arrangement of a noble gas, many elements, especially among the metals, form ions that do not have a noble-gas electron arrangement. Use the periodic table, Figure 2.14, to determine which of the following ions has a noble-gas electron arrangement, and which do not. For those that do, indicate the noble-gas arrangement they match: a) Ti(4+) b) Mn(2+) c) Pb(2+) d) Te(2-) e) Zn(2+)
a) Ar b) does not, V c) does not, Hg d) Xe e) does not, Ni
How many protons, neutrons and electrons are in an atom of a) 138 Ba b) Phosphorous - 31
a) Ba 138 - 56 = 82 Neutrons, 56 Protons, 56 Electrons b) P 31 - 15 = 16 Neutrons, 15 Protons, 15 Electrons
The structural formula for ethane is (see image): a) what is the molecular formula for Methane? b) What is its empirical formula? c) Can we infer from this drawing that the H-C-H bond angles are 90 degrees?
a) C2H6 b) CH3 c) No, it only shows where the atoms are in relation to the central structures
Write the Empirical Formulas for a) Glucose, a substance also known as either blood sugar or dextrose - molecular formula C6H12O6 b) nitrous oxide, a substance used as an anesthetic and commonly called laughing gas - molecular formula N2O
a) CH2O b) N2O
Consider the following four formulas: SO2, B2H6, CO, C4H2O2. Which of these formulas could be. a) only an empirical formula b) only a molecular formula c) either a molecular or an empirical formula
a) CO and SO2 b) B2H6 and C4H2O2 c) SO2 and CO
Calcium Bicarbonate is also called calcium hydrogen carbonate a) write the formula for this compound b) predict the formulas for potassium bisulfate and lithium, dihydrogen phosphate
a) Ca(HCO3)2 b) KHSO4 and LiH2PO4
Give the chemical formulas for a) hydrobromic acid b) carbonic acid
a) HBr b) H2CO3
Name the acids a) HCN b) HNO3 c) H2SO4 d) H2SO3
a) Hydrocyanic acid b) Nitric Acid c) Sulfuric Acid d) Sulfurous Acid
Write the empirical formula for the compound formed by a) Na+ and PO4(3-) b) Zn(2+) and SO4(2-) c) Fe(3+) and CO3(2-)
a) Na3PO4 b) ZnSO4 c) Fe2(CO3)3
Name the ionic compounds a) K2SO4 b) Ba(OH)2 c) FeCl3
a) Potassium Sulfate b) Barium Hydroxide c) Iron(III)Chloride
Based on the formula for the sulfate ion, predict the formula for (a) the selenate ion and (b) the selenite ion. (Sulfur and selenium are both in group 6A and form analogous oxyanions.)
a) SeO4(2-) b) SeO3(2-)
When carbon and oxygen react, two different compounds can form depending on the conditions. Compound A contains 1.333 g of oxygen per gram of carbon, whereas compound B contains 2.666 g of oxygen per gram of carbon. a) Does this observation illustrate the law of conservation of mass or the law of multiple proportions? b) If compound A has an equal number of oxygen and carbon atoms, what can we conclude about the composition of compound B?
a) The law of multiple proportions, because whether or not Compound A or B forms, they will always be in the same ratio of O-C (1:1 or (2:1) b) Compound B must contain 2 oxygen atoms per carbon
Give a reason why each of the following statements is a safe prediction: a) Every compound of Rb with a nonmetal is ionic in character b) Every compound of nitrogen with a halogen element is a molecular compound c) The compound MgKr2 does not exist d) Na and K are very similar in the compounds they form with nonmetals e) If contained in an ionic compound, calcium (Ca) will be in the form of the double charged ion, Ca2+.
a) This is true because Rb is a metal b) This is true because Nitrogen and all halogens are nonmetals, which only make molecular compounds c) MgKr2 is not possible because Kr2 is a noble gas an unreactive (wouldn't bond with anything) d) This is true because they both form +1 ions and are metals, meaning they will react similarly with nonmetals e) This is true because Ca2+ is its most stable ion for calcium
In which of the following species is the difference between the number of protons and the number of electrons largest? a) Ti(2+) b) P (3-) c) Mn d) Se (2-) e) Ce (4+)
a) Ti = 21 P, 19 E b) P = 15 P, 18 E c) Mn = 25 P, 25 E d) Se = 34 P, 36 E e) Ce = 58 P, 54 E Answer: E
Based on the formula for the sulfate ion, predict the formula for (a) the selenate ion and (b) the selenite ion. (Sulfur and selenium are both in group 6A and form analogous oxyanions.)
a)SeO4(2-) b) SeO3(2-)
Space-filling model
depicts what a molecule would look like if the atoms were scaled up in size
Ball-and-stick models
shows atoms as balls and bonds as sticks
Atomic weight
the average mass of atoms of an element; numerically equal to the mass in grams of one mole of an element Sum of all isotope masses x fractional isotope abundance Ex: Naturally occurring carbon is composed of 98.93% 12-C and 1.07% 13 C. The masses of these isotopes are 12 amu and 13.00335 amu. (0.9893)(12 amu) + (0.0107)(13.00335 amu) = 12.01 amu
Electronic Charge
the negative charge carried by an electron, 1.602x10^-19 C
Mass Number
the number of protons AND neutrons in the atom
The Law of Contstant Composition
the relative numbers and kinds of atoms are constant
Electromagnetic Force
these are attractive or repulsive forces that act between either electrically charged or magnetic objects Coulumb's Law - describes the magnitude of the electrical force between two charged particles F = (kxQ1xQ2)/d^2 Q1 and Q2 are magnitudes of the charges d is the distance between their centers k is a constant
What is the empirical formula for manganese(II) oxide − Mn2O, MnO, or MnO2?
MnO
Naming Acids
Acids containing anions whose names end in "-ide" are named by changing the ide" ending to "-ic" and adding the prefix "hydro-" ex: hydrochloric acid Acids containing anions whose names end in "-ate" or "-ite" are named by changing "-ate" to "-ic" and "-ite" to "-ous" and then adding the word acid ex: Chlorate becomes chloric acid
The most common ions for silver, zinc, and scandium are Ag+, Zn2+, and Sc3+. Locate the boxes in which you would place these ions in this table. Which of these ions has the same number of electrons as a noble-gas element?
Ag+ is a transition metal Zn2+ is a transition metal SC3+ is most similar to the noble gas Ar
Plum-Pudding Model
An atom has a overall positive sphere, with electrons embedded like raisins/seeds At first, this was supported by Rutherford's gold foil experiment until they looked at the deflection of electrons at larger angles
Polyatomic Ions
An electrically charged group of two or more atoms
The atomic weight of Copper, Cu, is listed as 63.546. Which statement is false? (a) All the copper atoms have 29 protons in the nucleus (b) Copper is a mixture of at least two isotopes (c) The dominant isotopes of Cu must be Cu 63 and Cu 64 (d) All neutral atoms of copper have the same number of electrons (e) The number of electrons in a copper atom is independent of its atomic mass
Answer: (c)
Which of the following nonmetals will form an ionic compound with Sc(3+) that has a 1:1 ration of cations to anions? a) Na b) F c) O d) N
Answer: D
Isotopes
Atoms of the same element with different numbers of neutrons
Give the empirical formula for decaborane, whose molecular formula is B10H14
B5H7
Predict the charge expected for the most stable ion of barium and the most stable ion of oxygen.
Ba(2+) O(2-)
Which of these compounds are molecular? a) only CBr4 b) both CBr4 and P4O6 c) only FeS d) both CBr4 and FeS
Both CBr4 and P4O6 because they are composed solely of nonmetals
The formula for the bromate ion is analogous to that for the chlorate ion. Write the formula for the hypobromite and bromite ions.
BrO(-) and BrO2(-)
Name the anion obtained by removing one oxygen atom from the perbromate ion, BrO4(-)
Bromate
The Law of Multiple Proportions
If two elements (A and B) combine to form one compound, the masses of A with B are in the ratio of small whole numbers
Would you expect the number of α particles scattered at large angles in Rutherford's experiment to increase, decrease, or stay the same as the thickness of the gold foil increases?
Increase The gold has a positive charge, and alpha particles also have a positive charge (+2). If the gold foil was increased, then there would be a higher chance of them colliding and being repelled at large angles
Name the acid obtained by adding H+ to the iodate ion, IO3(-)
Iodic Acid
Mass of an Electron
Mass = 1.76x10^8 C/g Charge = -1.602x10^19 C Actual Mass = 1.602x10^-19 C/(1.76x10^8 C/g) = 9.10938 x 10^-28 g
