Chemistry Sch3U - Unit 1

Chemistry SCH3U
Unit 1
Lesson 1

Key Questions

1. List three physical properties and one chemical property of a) an iron nail * conducts heat and electricity well * solid at room temperature * ductile * rusts in water (chemical) b) gasoline * liquid at 20deg C * boils between 20 and 200 degrees Celsius * not soluble in water * flammable in the presence of oxygen (chemical)

2. People in a workplace should have access to MSDS sheets so that * chemicals can stored properly * chemicals can be handled properly * the situation of improper storage or handling can be dealt with quickly and safely

3.a) The atomic mass of an element on the periodic table is an average of the masses of the naturally-occurring isotopes.
b) According to the periodic table, the average mass of boron is 10.8u.
c) With an average mass of 10.8, and the choice being either boron-10 or boron-11, boron-11 should be most common because it is the nearest isotope to the average mass.

4. Round each number to the given number of significant digits.
a) 1.160 (two significant digits) 1.2
b) 0.002 305 (three significant digits) 0.002 31
c) 12 040 (three significant digits) 12 000

5. Write the answer to each calculation using the correct number of significant digits.
a) 12.6 mL – 2.03 mL = 10.6 mL
b) 10.0 g / 2.4 mL = 4.2 g/mL
c) 125 Aspirin tablets X 1.3 g / tablet = 162.5 g = 160 g

6. Complete the following table. Particle | Mass of subatomic particle (g) | Charge of subatomic particle | Location in atom | proton | 1.67 x 10^-24 | positive | nucleus | electron | 9.11 x 10^-28 | negative | outside the nucleus | neutron | 1.67 x 10^-24 | neutral | nucleus |
7. Complete the following table by filling in the boxes with the appropriate information for the neutral elements. Name of isotope | Atomic number | Mass number | Number of protons | Number of electrons | Number of neutrons | hydrogen-1 | 1 | 1 | 1 | 1 | 0 | boron-11 | 5 | 11 | 5 | 5 | 6 | magnesium-12 | 12 | 24 | 12 | 12 | 12 | zinc-68 | 30 | 68 | 30 | 30 | 38 | tin-119 | 50 | 119 | 50 | 50 | 69 | silicon-30 | 14 | 30 | 14 | 14 | 16 |
8. Compare the sizes of the elements in each pair by referring to your periodic table. State which element has a larger atomic radius, and explain your reasoning.
a) Ca and Se Calcium has a larger atomic radius because it has less protons, and less pull on nearby electrons, thus the calcium atom is less compressed than the selenium atom.
b) N and P Phosphorus has a larger atomic radius because it has an additional energy level, meaning that the valence electrons are farther from the nucleus, and thus suggesting that the atomic radius is greater than that of nitrogen.

9. Carbon has a higher first ionization energy than lithium because the carbon atom has more protons and a stronger hold on its valence electrons. The lithium atom is larger than the carbon atom, which indicates that its first ionization energy is lesser. Lastly, metal atoms generally have a lower Eion than non-metals. ELABORATE BOTHE REASONS:
Reason # 1Carbon has a higher first ionization energy than lithium because it has a smaller atomic radius and a higher positive nuclear charge. The higher positive nuclear charge results in a greater force of attraction on the electrons and, in fact, its smaller atomic radius. This stronger hold on the electrons means it takes more energy to knock free its outermost electrons.
REASON # 2. Lithium wants to lose the one electron it has in its outermost energy level, because in doing so, it achieves the same stable electron arrangement as the nearest noble gas, He. Therefore, the removal of the outermost electron in lithium does not require a lot of energy, hence the lower ionization energy. Carbon, on the other hand, will need to lose four electrons from its outermost energy level in order to achieve a stable electron arrangement of helium gas. Its outermost energy level is already half-filled, and it will require a lot more energy to remove one electron from its outermost energy level than it would for Lithium.

M.D. = 2

10. The correct order of increasing electron affinities is Mg < Al < Si < P < S.

11. Use Lewis structures and an equation to show why
a) barium forms a cation with a charge of 2+ Ba Ba^2+ + e^2-

b) nitrogen forms an anion with a charge of 3- N^3- + e^3- N

12. For each atom, state the charge of the ion that forms to reach a stable electron arrangement.
a) strontium 2+
b) lithium 1+
c) aluminum 3+
d) phosphorus 3-
e) fluorine 1-
f) sulfur 2-

13. Answer the following questions, based on Table 2.2: Properties of Group 1 and 2 Metals.
a) Cesium should be more reactive than potassium, because it has more energy levels and thus has less pull on nearby electrons, meaning that it more readily gives up its electrons in a reaction than potassium.
b) Beryllium should not react vigorously with water, as magnesium has very little reaction with water, and magnesium should be more reactive than beryllium.

14. Fluorine is generally more reactive than iodine because of its high electronegativity. With less energy levels, fluorine has a stronger pull on nearby electrons, bringing about much more rapid and stronger reactions than iodine does.

15.

16. Draw Lewis structures for each element.
a) silicon
b) arsenic
c) bromine
d) krypton

17. Name the compound that forms when each pair of elements combines.
a) sodium and nitrogen sodium nitride
b) iron (III) and fluorine iron fluoride
c) bromine and potassium potassium bromide

18. Use the crossover rule to write the formula for each compound.
a) strontium iodide Sr 2+ I 1- SrI2
b) mercury (II) oxide Hg 2+ O 2- Hg2O2 HgO
c) copper (II) phosphide Cu 2+ P 3- Cu3P2
d) sulfur (IV) oxide S 4- O 2- S2O4 SO2
e) nitrogen (III) oxide N 3- O 2- N2O3
f) iron (III) chloride Fe 3+ Cl 1- FeCl3
19. Identify the type of bond in each compound by looking at the positions of the elements that make up the compound in the periodic table. Explain your reasoning.
a) NaCl is an ionic bond because it is between a metal and non-metal atom.
b) SiCl4 is a covalent bond because it is between two non-metal atoms.
c) MgO is an ionic bond because it is between a metal and non-metal atom.
d) PbF2 is an ionic bond because it is between a metal and non-metal atom.
c) PI3 is a covalent bond because it is between two non-metal atoms.

20. For each compound in Key Question 19, calculate the electronegativity difference between the two atoms that form a bond.
a) NaCl has a EN of 2.1
b) SiCl4 has a EN of 1.2
c) MgO has a EN of 2.3
d) PbF2 has a EN of 2.2
e) PI3 has a EN of 0.4

21. Use an arrow to show the difference in polarity between the bonds in the following pairs of elements:
C--> Cl is a EN of 0.5, therefore the arrow length is short
Si --------> Cl is a EN of 1.2, therefore the arrow length is long
The arrowheads are both pointed at Cl because chlorine has the greatest electronegativity.
ELABORATE.
19.

The polarities are different between these two bonds because delta EN for Si-Cl is greater than delta EN for C-Cl. Chlorine is common in both the bonds; therefore we compare the atoms that are bonded to the chlorine atom. Silicon is less electronegative than carbon, hence the bonding electron for silicon is weakly held in comparison to the electrons of carbon. For this reason, the electron pair is pulled more strongly towards the chlorine atom than to silicon. The Si-Cl bond is therefore more polar than the Cl-Cl bond. Silicon and chlorine have a much higher polarity difference because their electronegativity difference is higher than carbon and chlorine. Silicon holds its electrons less tight than carbon, so chlorine can pull in the shared silicon valence electrons closer to its nucleus.
M.D. = 2
22. a) Non-metal elements combine to form molecular compounds. An example of this is the combination of hydrogen and oxygen to form water H2O.
b) Metal and non-metal ions are bound together by ionic bonds to form ionic compounds. An example of this is the combination of sodium and chlorine to form table salt NaCl.

23. The properties of two substances are given in the following table. Identify which of the two unknown substances is ionic and which is molecular. Briefly explain and justify your choice. Substance | Melting point (deg C) | Electrical conductivity in solid | Electrical conductivity in liquid | I | -123 | poor | poor | II | 2357 | poor | moderate |

Substance ‘I’ should be molecular because it has a low melting point and does not conduct well as a liquid.
Substance ‘II’ is likely ionic, as its melting point is extremely high and, though it is a poor conductor as a solid, in its liquid form is conducts electricity moderately.

24. How is the bonding in calcium oxide different from the bonding in carbon dioxide?
Calcium is a metal. In order for calcium to ionically bond with oxygen, calcium must give up two electrons.
Carbon dioxide molecules are bound covalently. Oxygen and carbon atoms share electrons to form a stable molecular compound.

25. a) An oxygen atom has six valence electrons.
b) and must share two electrons to be stable.
c)

26. How does the number of electrons in the valence energy level of a metal atom differ from the number of electrons in the valence energy level of a non-metal atom? * metal atoms are more reactive with less valence electrons because it is easier to give up electrons and complete the shell during a reaction * non-metal atoms are more reactive with more valence electrons because they require less electrons to complete the shell during a reaction
ADD: The number of electrons for a metal in the valence shell is less than four. For non-metals, the number of electrons in valence shell is more than four. Metals are left side of the periodic table, while non-metals are right side. Metals tend to lose electrons and then gaining a positive charge, whereas non-metals gain electrons (the valence shell) so they end up having a negative charge.
M.D. = 1

27. Draw the Lewis structure and structural diagram for each molecule.
a) hydrogen peroxide, H2O2

b) sulfur dichloride, SCl2

c) formaldehyde, CH2O

d) carbon disulfide, CS2

e) ethyne, C2H2
REVIEW LEWIS STRUCTURE FOR C) D) & E. c) b) formaldehyde, (used to preserve biological specimens)

d) carbon disulfide,

e) ethyne,

M.D. = 3

28. Write the chemical formula for the molecular compound formed by each pair of elements.
a) sulfur and bromine S^2- + Br^1- SBr2
b) oxygen and fluorine O^2- + F^1- OF2
c) carbon and chlorine C^4- + Cl^1- CCl4
d) nitrogen and oxygen N^3- + O^2- N2O3
e) chlorine and fluorine Cl^1- + F^1- ClF
29. Using the correct prefix, name each compound.
a) CCl4 carbon tetrachloride
b) PH3 phosphorus trihydride (PHOSPHINE)
c) CH4 carbon tetrahydride (METHANE)
d) PCl5 phosphorus pentachloride
e) NBr3 nitrogen tribromide
f) SiF4 silicon tetrafluoride

30. Some elements exist in the form of diatonic molecules. Where are these elements generally located in the periodic table?
The elements can be located in an upside down ‘L’ shape that begins with nitrogen and ends with iodine, and in addition there is hydrogen.
IN THE UPPER RIGHT-HAND SIDE OF THE PERIODIC TABLE.

31. An unknown element, ‘Z’, forms an oxide with the formula Z2O3.
a) The valence of Z is 3- REVIEW: 3+.
b) The compound would have the formula ZCl3 if Z bonded with chlorine.
M.D. = 1
32. Write the formula for each compound containing a polyatomic ion.
a) beryllium phosphate Be3(PO4)2
b) lead (IV) acetate Pb(C2H3O2)4
c) ammonium carbonate (NH4)2CO3
d) magnesium sulfate MgSO4
M.D. = 1
33. Write the name of each compound containing a polyatomic ion.
a) Ba3(PO4)2 barium phosphate
b) Hg(ClO3)2 mercury chlorate
c) Ag2SO4 silver sulfate
d) KOH potassium hydroxide
34. Decomposition reactions involve the breaking down of a compound into its comprised molecules or elements, and may occur spontaneously or it may result from external factors such as exposure to heat. Hydrogen Peroxide, 2H202, spontaneously decomposes into 2H2O and O2. Chemical decomposition is the opposite of chemical synthesis, which involves the bonding of two or more elements or compounds. An example of a synthesis reaction takes place when sodium combines with chlorine to form table salt. 35. State whether each reaction is a synthesis, decomposition, single displacement or a double displacement reaction.
a) heat + lead (II) oxide lead + oxygen gas - decomposition reaction
b) tin + silver nitrate tin (IV) nitrate + silver - single displacement reaction
c) sodium chloride + lead (II) nitrate sodium nitrate + lead (II) chloride - double displacement reaction
d) aluminum + oxygen gas aluminum oxide - synthesis reaction

36. Complete each equation by writing the formula of the product (a solid) formed. (Do not try to balance your chemical equations.) Then classify each reaction as a synthesis, decomposition, single displacement or double displacement reaction.
a) NaBr Na + Br2 - decomposition reaction
b) Ca + AlF3 Al + CaF2 - single displacement reaction
c) Ba + O2 BaO - synthesis reaction
d) MgS + HI MgI2 + H2S - double displacement reaction
e) Mg(OH)2 + HF MgF2 + H2O - double displacement reaction

M.D. = 3
37. Silver can not displace copper from copper (II) nitrate because silver is less reactive than copper, which is due to its higher electronegativity.

38. Use the activity series of both halogens and metals to determine whether a reaction will occur when each pair of substances is mixed together. If you predict that a reaction will not take place, write “no reaction”. If you predict that a reaction will take place, write the complete equation. (Do not try to balance the equations.)
a) Al (s) + CuSO4 (aq) Cu + Al2(SO4)3
b) Hg (s) + AlBr3 (aq) no reaction
c) Zn (s) + H2SO4 (aq) H2 + ZnSO4
d) Ca (s) + MgBr2 (aq) CaBr2 + Mg
e) Cu (s) + AlCl3 (aq) no reaction
f) Cl2 (aq) + NaI (aq) NaCl + I2
g) NaCl (aq) + I2 (aq) no reaction
M.D. = 2
39. Skin allergies caused by exposure to nickel are common. Human sweat can slowly corrode nickel from nickel-containing objects such as 10 karat gold jewellery. The nickel ions that are released by this process can cause skin irritations. Wearing 18 karat gold jewellery can help to eliminate nickel allergies. Explain why, using your knowledge of the reactivity of metals and the activity series. * Nickel is displaced by sodium from human perspiration to form nickel salts, which irritate the skin. 18-karat gold jewellery is 75% gold, and therefore contains less of the metal alloys that cause skin irritations.

40. Copper is often used for water pipes. Use the activity series to explain why copper is better to use than other metals such as lead, iron and zinc. * iron pipes combine with oxygen to form iron oxide, which contaminates drinking water * lead pipes contaminate drinking water with lead, which is highly toxic * zinc may dissolve in water, causing pipes to disintegrate and an undesirable flavour * copper does not react with water, is generally non-toxic to humans and also inhibits the growth of bacteria