Test 2 Pre-Test Grade: «grade» Subject: Test 2 - Ch 2-9 Date: «date» OBJECTIVE: Administer this Practice Test 2 & thoroughly explain all incorrect answers.

1Fluorine belongs to group 7A. How many covalent bonds are formed between two fluorine atoms? A 1 B 2 C 3 D 4 EXPLANATION you have to do the Lewis Structure

2Molecules containing only polar covalent bonds ____. A are always polar B may or may not be polar C are always ionic D are always nonpolar Blue atom made this tetrahedral shape polar because of symmetry not polar because it is symmetrical. All atoms on central atom are the same EXPLANATION

3How many electrons can occupy a single molecular orbital? A 0 B 1 C 2 D 4 EXPLANATION All orbitals can only handle a maximum of 2 electrons.

4What are shared in a covalent bond? A ions B Lewis Structures C electrons D dipoles EXPLANATION the word covalent means that electrons are being shared by 2 atoms, and not removed from one to the other.

5What is the correct Lewis structure for hydrogen chloride, HCl? A a B b C c D d EXPLANATION Use my rules for figure out Lewis Structures, get total valence electrons, the use exceptions and octet rule to pass out electrons, then be sure the total valence electrons are there in the Lewis Str, no more, no less. Also see my vids on YouTube

6The symbol mm represents A micrometer B millimeter C milliliter D meter EXPLANATION mm is a definition found in Ch 2 p. 26, combining milli- prefix the base unit meter.

7Which of the following represents a compound? A H B H-3 C H2OH2O D O-16 EXPLANATION molecules of a compound have at least 2 different kinds of atoms

8Emission of light from an atom occurs when an electron ____. A drops from a higher to a lower energy level B jumps from a lower to a higher energy level C moves within its atomic orbital D falls into the nucleus electron is excited by energy from outside atom (jumps to higher energy level), the light is given off (photon) when it drops back to its ground state EXPLANATION

9Trends in the properties of elements in a group or period can be explained in terms of A binding energy B atomic number C electron configuration D electron affinity outer shell electrons (valence) determine ratios with which atoms combine to make molecules EXPLANATION

10How many electrons are shared in a double covalent bond? A none B one C two D four EXPLANATION each covalent bond is a "stick" and double = 2

11When a stable covalent bond forms, the potential energy of the atoms: A increases B decreases C remains constant D becomes zero energy increases lowest possible energy level is a set distance between 2 atoms in a bond. This graph shows relative energy of atoms as they move closer together distance betwee, atoms See ChemThink Tutorial on Chemical Bonding - screen 15 EXPLANATION

12A substance that forms a vapor is generally in what physical state at room temperature? A solid B liquid C gas D liquid or solid all substances have 3 states - solid, liquid & gas. This question is asking what is the original state of a substance that can be changed into a gas. EXPLANATION

13Which of the following measurements (of different masses) is the most accurate? A g B g C g D g The amount of accuracy a number shows is determined by the number of sig figs in the number. EXPLANATION

14In which of the following pair is the second particle listed larger than the first? A K, Ga B Pb, C C Br, Br - D Li, Li + Positive ions are smaller than the atoms they started out as. Negative ions are larger than the atoms they started out as. Relative sizes of two different atoms can be determined by use the trend for size. EXPLANATION

15What is the formula for sodium sulfate? A NaSO 4 B Na 2 SO 4 C Na(SO 4 ) 2 D Na 2 (SO 4 ) 2 Overall net charge on all molecules must be zero. If not, they will be consider ions EXPLANATION

16The shape of a molecule that has two covalent single bonds and no lone pairs on the central atom is ____. A tetrahedral B trigonal planar C trigonal pyramidal D linear Presence of unshared pair on this molecule and the shape it represents, rules it out as a possible answer. covalent bond covalent bond no unshared pairs EXPLANATION

17Which of the following elements can form diatomic molecules held together by triple covalent bonds? A carbon B oxygen C fluorine D nitrogen Diatomic column 17 nitrogen oxygen hydrogen EXPLANATION

18A mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together is called a(n) A dipole B Lewis structure C chemical bond D London force EXPLANATION chemical bond (c) look at ChemThink tutorial for Chemical Bonding

19The substance whose Lewis structure shows three covalent bonds is A H2OH2O B CH 2 Cl 2 C NH 3 D CCl 4 EXPLANATION

20What must occur for a change to be a chemical reaction? A There must be a change in chemical properties. B There must be a change in physical properties. C The change must involve a change in mass. D The change must involve a change in volume. EXPLANATION see Ch 3 on chem vs physical changes

21As it travels through space, electromagnetic radiation A exhibits wavelike behavior B loses energy C varies in speed D releases photons EXPLANATION See Ch 5 on light, p. 118 re wave and p. 122 re particle

22What is the formula for the compound formed by lead(II) ions and chromate ions? A PbCrO 4 B Pb 2 CrO 4 C Pb 2 (CrO 4 ) 3 D Pb(CrO4) 2 roman numerals after the name of a metal tell you the charge on a metal that can have more than one charge. So "lead (II)" means that the ion of lead (the metal) has a 2+ charge Charges on Pb and Chromate are equal, so we only need one of each. EXPLANATION

P1 P2P3 P4 P P1 P2 P P5 P6 P1 P2P