Chemistry Unit 2 Test Review

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Questions and Answers

How many bonding electrons does an atom of magnesium have?

2 (correct)

What substance could be an ionic?

1770°C

35°C (correct)

2630°C

2220°C

Why does argon exist as stable, unbonded atoms?

Argon has a full valence shell with 8 electrons (octet rule).

What molecule has a linear shape around its central atom?

CO2 Signup and view all the answers

What fifth period element has 2 lone pairs and 2 bonding electron in its valence level?

Se Signup and view all the answers

Which molecule possesses a triple covalent bond?

C2H2 Signup and view all the answers

What is the shape around the central atom in a molecule of H2CO?

Trigonal planar Signup and view all the answers

Identify the following bonds as ionic, polar covalent, slightly polar covalent or ionic. Use appropriate notation to indicate bond dipoles. K-F

ionic Signup and view all the answers

Which compound can dissolve in water?

NH3 Signup and view all the answers

Water, H2O, has a considerably higher boiling temperature than hydrogen sulfide, H2S. How can this be explained?

Water can form hydrogen bonds, which are stronger intermolecular forces than the dipole-dipole interactions present in hydrogen sulfide. Signup and view all the answers

What force of attraction is characterized by the formation of temporary dipoles or instantaneous and induced dipoles?

London Dispersion forces Signup and view all the answers

What chemical bond arises when two atoms simultaneously attract a pair of valence electrons?

Covalent bond Signup and view all the answers

What substance will have the highest boiling point? CI4, CuZn, KI, SiS2

SiS2 Signup and view all the answers

What describes the bonding in NaCl?

Ionic bonding Signup and view all the answers

What substance will NOT conduct electricity? Ba(l) Ba(s) BaCl2(l) BaCl2(s)

Ba(s) Signup and view all the answers

What substance will have the strongest London Dispersion forces?

S8 Signup and view all the answers

Which substance exists at room temperature as a solid crystal lattice consisting of uncountable cations and anions?

Ionic compounds Signup and view all the answers

Which substance has the lowest boiling point?

HBr Signup and view all the answers

An unknown substance was found to be very hard, had a very high melting point, did not conduct electricity in the solid or molten state and was insoluble in water. What is the identity of the unknown solid substance?

Diamond Signup and view all the answers

Draw a correct electron dot diagram for CH3COOH(2)

H : O : C : : O : H | H : C : H H Signup and view all the answers

Provide a detailed analysis of the intermolecular forces present in each of these substances and predict which of them has the higher boiling point. (a) CH3PH2 and CH3Cl

CH3PH2 has dipole-dipole interactions and London Dispersion forces, while CH3Cl has dipole-dipole interactions and London Dispersion forces. CH3PH2 has a higher boiling point because the dipole-dipole interactions are stronger in CH3PH2 than in CH3Cl, due to the larger difference in electronegativity between P and H compared to C and Cl. Signup and view all the answers

Provide a detailed analysis of the intermolecular forces present in each of these substances and predict which of them has the higher boiling point. (b) CH3OH and C5H12

CH3OH has hydrogen bonding and London Dispersion forces, while C5H12 only has London Dispersion forces. CH3OH has a higher boiling point because hydrogen bonding is a much stronger intermolecular force than London Dispersion forces. Signup and view all the answers

Complete the following table: a) CH3NH2 Electron dot: Name the Shape: VSEPR diagram (include bond dipole if polar): Polarity:

Electron dot: H | H : N : H | H : C : H H Name the Shape: Trigonal pyramidal VSEPR diagram: H | H : N : H \ + H : C : H H Polarity: Polar Signup and view all the answers

Explain using a theory of metallic bonding why tin strips are malleable.

Tin atoms are arranged in a lattice with delocalized electrons. When a force is applied to a tin strip, the layers of atoms can slide past each other because of the delocalized electrons, allowing the metal to deform without breaking. Signup and view all the answers

Explain using a theory of ionic bonding why calcium chloride is brittle and shatters under force.

Calcium chloride (CaCl2) is an ionic compound with a rigid lattice structure due to the strong electrostatic forces between the positively charged calcium ions (Ca2+) and the negatively charged chloride ions (Cl-). When a force is applied, the ions are unable to slide past each other, resulting in the lattice fracturing and shattering. Signup and view all the answers

Based on a relative force analysis, arrange the following substances in order of decreasing boiling point (highest to lowest) Explain why? Cn (diamond), Mg, C4H10, C4H9OH, C4H8(OH)2, C4H9Br, MgS, CH4

Cn (diamond) > MgS > Mg > C4H8(OH)2 > C4H9OH > C4H9Br > C4H10 > CH4 Signup and view all the answers

What substance will have the highest boiling point?

SiS2 Signup and view all the answers

What substance will NOT conduct electricity?

Ba(s) Signup and view all the answers

Provide a detailed analysis of the intermolecular forces present in each of these substances and predict which of them has the higher boiling point. (a) CH3PH2 and CH3Cl (b) CH3OH and C5H12

(a) CH3PH2 has dipole-dipole and London dispersion forces, while CH3Cl has dipole-dipole and London dispersion forces. CH3PH2 has a slightly higher boiling point due to its polar bond with a higher difference in electronegativity. (b) CH3OH has hydrogen bonding and London dispersion forces, while C5H12 has only London dispersion forces. CH3OH has a much higher boiling point due to hydrogen bonding, which is a stronger intermolecular force compared to London dispersion forces. Signup and view all the answers

Complete the following table: a) CH3NH2 Electron dot: Name the Shape: VSEPR diagram (include bond dipole if polar): Polarity: b) CH3OH Electron Dot: Name the Shape: VSEPR diagram (include bond dipole if polar): Polarity:

a) CH3NH2 Electron dot: H : N: H H C H : H Name the Shape: Trigonal pyramidal VSEPR diagram (include bond dipole if polar): N H H C H H : bond dipole Polarity: Polar b) CH3OH Electron Dot: H : O: H C H : H Name the Shape: Tetrahedral VSEPR diagram (include bond dipole if polar): O H H C H H : bond dipole Polarity: Polar Signup and view all the answers

Which of the following compounds would be soluble in a solvent such as carbon tetrachloride, CCl4? Explain why?.

Br2 Signup and view all the answers

Which substance, either an ionic compound or alloy would you expect to be easily shaped into a nail? Explain your choice?

Alloy. Alloys are mixtures of metals that often have enhanced mechanical properties, making them more malleable and easier to shape into a nail. Ionic compounds are brittle and would shatter if force is applied to shape them. Signup and view all the answers

Why are metals excellent conductors of electrical current? Explain.

Metals have delocalized electrons that are not bound to a particular atom in the metal’s lattice. These electrons can move freely throughout the material, carrying an electrical charge and readily conducting electricity. Metals are good conductors of electrical current due to the free movement of electrons. Signup and view all the answers

Why ionic compounds are solids at room temperature? Explain.

Ionic compounds are held together by strong electrostatic forces between positively and negatively charged ions. The ions arrange themselves into a rigid, crystalline structure at room temperature due to strong electrostatic attractions between oppositely charged ions. The strong bonds require lots of energy to break, to melt or boil. Signup and view all the answers

Sketch an electron sea model for the silver (90%) and copper (10%).

A simplified electron sea model shows the arrangement of metal ions in a lattice structure with a 'sea' of delocalized electrons surrounding and moving freely. The electron sea model helps to explain the conductive and malleable properties of metals like silver and copper. The exact proportions of silver and copper ions and electrons within the lattice model are dependent on the specific alloy composition. Signup and view all the answers

Study Notes

Review Sheet Unit 2 Test Chem 2202

Magnesium atoms have 2 bonding electrons
Substances with high boiling points may be ionic or polar covalent.
Poor electrical conductivity in a solid state indicates that the substance may be ionic or covalent.
Substances that conduct electricity in both liquid and solid states are usually metallic.
Argon exists as individual atoms due to lack of need for electron sharing.
Linear shaped molecules contain a central atom with two identical atoms at the ends, and no other atoms attached to the central atom.
Triple covalent bonds are formed by sharing three pairs of electrons between two atoms (e.g., in C2H2).
A fifth period element with two lone pairs and two bonding electron pairs in its valence level could be sulfur (or Selenium, Tellurium, Polonium but sulfur is likely based on the period).
The shape around the central carbon atom in H2CO is trigonal planar.
Potassium Fluoride (KF) is an ionic bond, chlorine-chlorine (Cl-Cl) is a nonpolar covalent bond, Silicon-Phosphorus (Si-P) is a polar covalent bond, and Phosphorus-Chlorine (P-Cl) is a polar covalent bond.
Compounds soluble in water usually have polar covalent bonds.
Water has a higher boiling point than hydrogen sulfide because water molecules form stronger hydrogen bonds.
Temporary/instantaneous and induced dipoles are a type of intermolecular force.
A chemical bond occurs when two atoms share one or more pairs of electrons.
Substances with high boiling points usually have stronger intermolecular forces, such as higher molecular weight leading to stronger London Dispersion forces, hydrogen bonds, or dipole-dipole interactions.
Sodium Chloride (NaCl) has ionic bonding.
Substances that do not conduct electricity in either liquid or solid state are likely nonpolar or poor conductors.
Substances with stronger London Dispersion forces have higher boiling points (e.g., larger molecules).
Ionic compounds are crystalline solids composed of cations and anions.
Electron dot diagrams represent valence electrons.
Metallic bonding involves a "sea of electrons" surrounding positive metal ions.
Due to the nature of ionic bonds, calcium chloride (and similar) is brittle and shatters under force.
Intermolecular forces influence boiling points, with stronger interactions leading to higher boiling points.
Solubility depends on the polarity of the solute and the solvent. like dissolves like.
Substances with high melting points and hardness are generally ionic compounds which are difficult to shape .

Additional Questions and Concepts

Analyze intermolecular forces in different substances (e.g., CH₃PH₂, CH₃Cl, CH₃OH, and C₅H₁₂) to predict boiling points.
Determine the solubility of different substances in a solvent like carbon tetrachloride (CCl₄) based on polarity.
Identify the substance with the lowest boiling point from a list of substances.
Understand the properties of substances based on the nature of their bonding.
Explain metallic bonding and its impact on malleability of metals.
Explain ionic bonding and its connection to brittleness in ionic compounds.

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Prepare for your Chemistry Unit 2 test with this comprehensive review sheet. This quiz covers key concepts such as bonding electrons, molecular shapes, and the properties of ionic and covalent substances. Refresh your understanding of essential chemical principles to excel in your exam.