2 2. Which combination of atoms can form a polar covalent bond? A) N and NB) H and HC) Na and BrD) H and BrCorrect Answer: Option D - H and Br
3 3. As a bond between a hydrogen atom and a sulfur atom is formed, electrons are: A) Shared to form a covalent bondB) Shared to form an ionic bondC) Transferred to form an ionic bondD) Transferred to form a covalent bondCorrect Answer: Option A - Shared to form a covalent bond
4 4. Atoms of which element can bond to each other to form chains, rings, and networks? A) HydrogenB) FluorineC) OxygenD) CarbonCorrect Answer: Option D - Carbon
5 5. Which element has an atom with the greatest attraction for electrons in a chemical bond? A) ArsenicB) NitrogenC) BismuthD) PhosphorusCorrect Answer: Option B - NitrogenElectronegativity, denoted by symbol χ, is a chemical property that describes the ability of an atom (or, more rarely, a functional group) to attract electrons (or electron density) towards itself in a covalent bond.
6 6. Which formula represents a polar molecule? A) Br2B) CH4C) CO2D) NH3Correct Answer: Option D - NH3
7 7. What can be concluded if an ion of an element is smaller than an atom of the same element? A) The ion is negatively charged because it has fewer electrons than the atom.B) The ion is negatively charged because it has more electrons than the atom.C) The ion is positively charged because it has fewer electrons than the atom.D) The ion is positively charged because it has more electrons than the atom.Correct Answer: Option C - The ion is positively charged because it has fewer electrons than the atom.Ionic radius trend -Cations (positive ions) are always smaller than their parent atoms and anions (negative ions) are always larger.
8 8. Which compound contains both ionic and covalent bonds? A) Sodium nitrateB) AmmoniaC) MethaneD) Potassium chlorideCorrect Answer: Option A - Sodium nitrate
9 9. Which bond has the greatest ionic character? A) H---NB) H---FC) H---ClD) H---OCorrect Answer: Option B - H---FH has an electronegativity of 2.1 and F has an electronegativity of 4.0. Subtract the two values and the difference is 1.9. Ionic bonds have differences of 1.7 or greater.
10 11. A solid substance is an excellent conductor of electricity 11. A solid substance is an excellent conductor of electricity. The chemical bonds in this substance are most likelyA) Ionic, because the valence electrons are shared between atomsB) Ionic, because the valence electrons are mobileC) Metallic, because the valence electrons are stationaryD) Metallic, because the valence electrons are mobileCorrect Answer: Option D - Metallic, because the valence electrons are mobile
11 12. The reaction that joins thousands of small, identical molecules to form one very long molecule is called:A) EsterificationB) PolymerizationC) FermentationD) SubstitutionCorrect Answer: Option B - Polymerization
12 14. Which statement describes what occurs as two atoms of bromine combine to become a molecule of bromine?A) Energy is absorbed as a bond is formed.B) Energy is absorbed as a bond is broken.C) Energy is released as a bond is formed.D) Energy is released as a bond is broken.Correct Answer: Option C - Energy is released as a bond is formed.
13 15. An oxygen molecule contains a double bond because the two atoms of oxygen share a total of A) 1 electronB) 3 electronsC) 2 electronsD) 4 electronsCorrect Answer: Option D - 4 electrons
14 23. To become a calcium ion a calcium atom must: A) Gain 2 ionsB) Gain 2 protonsC) Lose 2 neutronsD) Lose 2 electronsCorrect Answer: Option D - Lose 2 electronsAn ion is an atom (or group of atoms) that has gained or lost one or more electrons. Many main group elements gain or lose electrons such that they have the same number of electrons as a Noble gas. Calcium, and all of the alkaline earth elements, lose two electrons. Since electrons are negatively charged, the loss of electrons gives the resulting ion a positive charge.
15 4) NH3 is a polar molecule. Br2 and CO2 are linear, non-polar molecules. CH4 is a symmetrical, non-polar molecule
16 (3) N is the correct answer. Electronegativity indicates how strongly an atom of an element attracts electrons in a covalent bond. See table S. Also, by memorizing the electronegativity trend of the periodic table, we can see that electronegativity increases from bottom to top in a column and from left to right across a group.
17 (2) Is the correct answer. The definition of a covalent bond is electrons that are shared between 2 atoms. Hydrogen and Sulfur share electrons to form a covalent bond. This compound is similar to Water, where 2 hydrogens share electrons with one oxygen.
25 1. Which sequence of Group 18 elements demonstrates a gradual decrease in the strength of the Van der Waals forces?A) Ar, Kr, Ne, XeB) Xe, Kr, Ar, NeC) Kr, Xe, Ar, NeD) Ne, Ar, Kr, XeCorrect Answer: Option B - Xe, Kr, Ar, NeThe van der Waals force (or van der Waals interaction) is the attractive or repulsive force between molecules (or between parts of the same molecule) other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules. These forces decrease as the molecule gets smaller and increase as the molecule increases. Therefore the Van der Waals forces would also be decreasing