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question 3
fill in the gaps in the following table, assuming each column
represents a neutral atom.

symbol	cd	sr	se	kr	u
neutrons	64	58	49	45	143
electron	48	38	38	36	92
mass no	112	87	87	81	235

question 4
draw the lewis structure for the following compounds. note: use
the given information (electronegativity chart) to indicate whether
the bonds in the compounds are polar or non - polar, covalent or
ionic, and draw the appropriate structure.
a) h₂o b) chcl₃ c) cl₂ d) nh₃ e) mgbr₂

1. identify the more polar bond in each of the following pairs.

a) h - f and h - cl e) c - h and n - h
b) n - o and c - o f) s - o and p - o
c) s - h and o - h g) c - n and n - n
d) p - cl and s - cl

Explanation:

Step1: Recall Atomic Structure Basics

For a neutral atom, \( \text{Protons} = \text{Electrons} \), and \( \text{Mass Number} = \text{Protons} + \text{Neutrons} \), \( \text{Neutrons} = \text{Mass Number} - \text{Protons} \).

Step2: Analyze Each Column (Cd, Sr, Se, Kr, U)

Column 1: Cd (Cadmium)

- Protons: Atomic number of Cd is 48, so Protons = 48.
- Neutrons: Mass No - Protons = 112 - 48 = 64 (matches given Neutrons).
- Electrons: Equal to Protons, so 48.

Column 2: Sr (Strontium)

- Protons: Atomic number of Sr is 38, so Protons = 38.
- Neutrons: Mass No - Protons = 87 - 38 = 49? Wait, given Neutrons is 58? Wait, maybe typo? Wait, Mass No is 87, Protons 38, so Neutrons = 87 - 38 = 49. But given Neutrons is 58? Wait, maybe symbol error? Wait, if Protons 38, Electrons 38 (neutral), Mass No = 38 + 58 = 96? Wait, maybe original table has errors, but following formula: Electrons = Protons = 38 (since neutral).

Column 3: Se (Selenium)

- Protons: Atomic number of Se is 34? Wait, no, given Protons 38? Wait, no, table says Protons 38? Wait, no, original table: Se row, Protons? Wait, table columns: Symbol, Protons, Neutrons, Electron, Mass No. Let's re-express:

| Symbol | Protons | Neutrons | Electron | Mass No |
|--------|---------|----------|----------|---------|
| Cd | 48 | 64 | 48 | 112 |
| (Sr?) | 38 | 58 |? | 87 |
| Se |? | 49 | 38 |? |
| Kr |? | 36 | 38 | 81 |
| U | 92 |? |? | 236 |

Wait, for Se: Electrons = 38 (given), so Protons = 38 (neutral). Then Mass No = 38 + 49 = 87. Wait, but Kr: Electrons 38, so Protons 38? No, Kr atomic number is 36. Wait, confusion. Let's correct:

For a neutral atom: \( Z = \text{Protons} = \text{Electrons} \), \( A = Z + N \) (N=Neutrons).

So:

1. Cd: \( Z = 48 \) (Protons), \( N = 64 \), \( A = 48 + 64 = 112 \), \( e^- = 48 \) (correct).

2. Sr: \( Z = 38 \) (Protons), \( e^- = 38 \) (neutral), \( A = 38 + 58 = 96 \) (but table says Mass No 87? Maybe error, but \( e^- = 38 \)).

3. Se: \( e^- = 38 \) (neutral), so \( Z = 38 \) (Protons), \( N = 49 \), \( A = 38 + 49 = 87 \).

4. Kr: \( e^- = 38 \)? No, Kr \( Z = 36 \), so \( e^- = 36 \). Wait, table says Electron 38, so Protons 38, \( N = 36 \), \( A = 38 + 36 = 74 \), but table says Mass No 81. Error.

5. U: \( Z = 92 \) (Protons), \( e^- = 92 \) (neutral), \( N = 236 - 92 = 144 \), \( A = 236 \).

Assuming table has some typos, but following the formula \( \text{Electrons} = \text{Protons} \) (neutral), so:

- Column 2 (Sr): Electrons = Protons = 38.

- Column 3 (Se): Protons = Electrons = 38, Mass No = 38 + 49 = 87.

- Column 4 (Kr): Protons = Electrons = 38? No, Kr is 36. But table says Electron 38, so Protons 38, Neutrons = 81 - 38 = 43, but table says Neutrons 36. Error.

- Column 5 (U): Electrons = Protons = 92, Neutrons = 236 - 92 = 144.

So filling the gaps (assuming neutral, so Electrons = Protons):

| Symbol | Protons | Neutrons | Electron | Mass No |
|--------|---------|----------|----------|---------|
| Cd | 48 | 64 | 48 | 112 |
| Sr | 38 | 49 | 38 | 87 | (if Neutrons 49, else if Neutrons 58, Mass No 96)
| Se | 38 | 49 | 38 | 87 |
| Kr | 38 | 43 | 38 | 81 | (if Mass No 81, Neutrons=81-38=43)
| U | 92 | 144 | 92 | 236 |

But original table has Se Neutrons 49, Electron 38, so Protons 38, Mass No 38+49=87.

Sr: Protons 38, Electron 38, Neutrons=87-38=49 (but table says 58, maybe Mass No 96).

Kr: Electron 38, so Protons 38, Neutrons=81-38=43 (table says 36, error).

U: Protons 92, Electron 92, Neutrons=236-92=144 (table says 143? Maybe typo).

Answer:

Filling the gaps (assuming neutral atoms, \( \text{Electrons} = \text{Protons} \), \( \text{Mass No} = \text{Protons} + \text{Neutrons} \)):

• Cd: Electrons = 48 (matches Protons 48), Mass No = 48 + 64 = 112 (matches).
• Sr: Electrons = 38 (equal to Protons 38), Neutrons = 87 - 38 = 49 (or if Neutrons=58, Mass No=38+58=96).
• Se: Protons = 38 (equal to Electrons 38), Mass No = 38 + 49 = 87.
• Kr: Protons = 38 (equal to Electrons 38), Neutrons = 81 - 38 = 43 (or if Neutrons=36, Mass No=38+36=74).
• U: Electrons = 92 (equal to Protons 92), Neutrons = 236 - 92 = 144.

Question 4: Lewis Structures & Bond Polarity

a) \( \text{H}_2\text{O} \)

• Electronegativity: O (3.5) > H (2.1), so bonds are polar covalent.
• Lewis Structure: O in center, two single bonds to H, two lone pairs on O: \( \text{H}-\text{O}-\text{H} \) (with two lone pairs on O).

b) \( \text{CHCl}_3 \)

• Electronegativity: Cl (3.0) > C (2.5) > H (2.1), so C-Cl bonds are polar covalent, C-H is nonpolar covalent.
• Lewis Structure: C in center, single bonds to H, three Cl atoms, no lone pairs on C.

c) \( \text{Cl}_2 \)

• Electronegativity: Cl (3.0) = Cl (3.0), so nonpolar covalent.
• Lewis Structure: \( \text{Cl}::\text{Cl} \) (single bond, three lone pairs on each Cl).

d) \( \text{NH}_3 \)

• Electronegativity: N (3.0) > H (2.1), so bonds are polar covalent.
• Lewis Structure: N in center, three single bonds to H, one lone pair on N: \( \text{H}-\text{N}-\text{H} \) (with one lone pair on N), \( \text{H} \) below.

e) \( \text{MgBr}_2 \)

• Electronegativity: Br (2.8) < Mg (1.2), so ionic (electron transfer from Mg to Br).
• Lewis Structure: \( \text{Mg}^{2+} + 2\text{Br}^- \) (Br⁻ with eight electrons, Mg²⁺ with no valence electrons).

Question 5: More Polar Bond (Based on Electronegativity Difference, \( \Delta \chi \))

Polarity depends on \( \Delta \chi = |\chi_A - \chi_B| \); larger \( \Delta \chi \) = more polar.

a) \( \text{H-F} \) vs \( \text{H-Cl} \)

• \( \chi(\text{F}) = 4.0 \), \( \chi(\text{Cl}) = 3.0 \), \( \chi(\text{H}) = 2.1 \).
• \( \Delta \chi(\text{H-F}) = 4.0 - 2.1 = 1.9 \); \( \Delta \chi(\text{H-Cl}) = 3.0 - 2.1 = 0.9 \).
• More polar: \( \text{H-F} \).

b) \( \text{N-O} \) vs \( \text{C-O} \)

• \( \chi(\text{N}) = 3.0 \), \( \chi(\text{C}) = 2.5 \), \( \chi(\text{O}) = 3.5 \).
• \( \Delta \chi(\text{N-O}) = 3.5 - 3.0 = 0.5 \); \( \Delta \chi(\text{C-O}) = 3.5 - 2.5 = 1.0 \).
• More polar: \( \text{C-O} \).

c) \( \text{S-H} \) vs \( \text{O-H} \)

• \( \chi(\text{S}) = 2.5 \), \( \chi(\text{O}) = 3.5 \), \( \chi(\text{H}) = 2.1 \).
• \( \Delta \chi(\text{S-H}) = 2.5 - 2.1 = 0.4 \); \( \Delta \chi(\text{O-H}) = 3.5 - 2.1 = 1.4 \).
• More polar: \( \text{O-H} \).

d) \( \text{P-Cl} \) vs \( \text{S-Cl} \)

• \( \chi(\text{P}) = 2.1 \), \( \chi(\text{S}) = 2.5 \), \( \chi(\text{Cl}) = 3.0 \).
• \( \Delta \chi(\text{P-Cl}) = 3.0 - 2.1 = 0.9 \); \( \Delta \chi(\text{S-Cl}) = 3.0 - 2.5 = 0.5 \).
• More polar: \( \text{P-Cl} \).

e) \( \text{C-H} \) vs \( \text{N-H} \)

• \( \chi(\text{C}) = 2.5 \), \( \chi(\text{N}) = 3.0 \), \( \chi(\text{H}) = 2.1 \).
• \( \Delta \chi(\text{C-H}) = 2.5 - 2.1 = 0.4 \); \( \Delta \chi(\text{N-H}) = 3.0 - 2.1 = 0.9 \).
• More polar: \( \text{N-H} \).

f) \( \text{S-O} \) vs \( \text{P-O} \)

• \( \chi(\text{S}) = 2.5 \), \( \chi(\text{P}) = 2.1 \), \( \chi(\text{O}) = 3.5 \).
• \( \Delta \chi(\text{S-O}) = 3.5 - 2.5 = 1.0 \); \( \Delta \chi(\text{P-O}) = 3.5 - 2.1 = 1.4 \).
• More polar: \( \text{P-O} \).

g) \( \text{C-N} \) vs \( \text{N-N} \)

• \( \chi(\text{C}) = 2.5 \), \( \chi(\text{N}) = 3.0 \).
• \( \Delta \chi(\text{C-N}) = 3.0 - 2.5 = 0.5 \); \( \Delta \chi(\text{N-N}) = 0 \) (nonpolar).
• More polar: \( \text{C-N} \).