<u>Answers:</u>
1)Which of the following formulas represents a molecular (i.e. covalent) compound?
B. H₂O
<u>Explanation</u>: CaCl, NaOH and LiF are ionic compounds. In H₂O the bonds between atoms are covalent bonds.
2)According to the Aufbau principle,
A. electrons enter orbitals of lowest energy first.
<u>Explanation:</u> Aufbau principle explains how the electrons are located in the different orbitals, starting with the first level of lowest energy to the last level as follows:
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²5f¹⁴6d¹⁰7p⁶
3)26.8 moles of argon contain how many atoms?
D. 1.61 × 1025 atoms
<u>Explanation</u>:
1 mol = 6.022 ₓ 10²³ atoms
atoms= 26.8 mol ₓ 6.022 ₓ 10²³ atoms/mol = 1.61 × 10²⁵ atoms
4)Group 17 (i.e. 7A) elements have _________ electron(s) in their valence shell.
C. 7
<u>Explanation:</u> in Group 17 are the halogen elements, which have 7 electrons in their valence shell, with an electronic configuration 1s² 2p⁵ (two electrons in s orbital and 5 electrons in p orbital)
5)In which of the following is the symbol for the ion and the number of electrons it contains given correctly?
K+; 18 electrons
<u>Explanation:</u> the atomic number of potassium element (K) is 19, so its number of electrons is 19. To form the cation K⁺, it must loss 1 electron to have 1 positive charge. The remaining electrons after losing an electron is 18.
6) In metallic bonding, the electrons
D. are in a "sea" around the protons of all the metal atoms.
Explanation: metallic bonding exists in metals (such as Fe, Ni, Cu). The electrons are not located in one particular atom, but they can move from one atom to another by forming a mass or "sea" of electrons surrounding the protons. For this reason, metals can conduct electricity.
