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CHAPTER 2 BASIC HOMEWORK

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Note: Order may differ!


 

Question 1

Question Image

REMEMBER: Number of protons is the same as asking for atomic number!



 

Explanation



  
 

Question 2

What is the mass number? (Refer to the question above).

 

Explanation

       

 

Question 3

What is the number of neutrons? (Referring to previous question)

 

Explanation

    # Neutrons = Mass Number - Protons (Atomic Number)

 

Question 4

What is the number of electrons?  (Referring to previous question)

 

Explanation

Number Electrons = Atomic Number - charge number (if charge is a positive number)


Number Electrons = Atomic Number + charge number (if charge is a negative number)


 

Question 5

Which of the following elements are diatomic molecules at room temperature?
(All answers must be correct to get credit.) 



Select one or more:
 Correct
 Correct
 Correct

 

Explanation

Memorize that H, N, O, F, Cl, Br, I are all diatomic molecules


  

 

Question 6

How many electrons does magnesium, Mg, need to lose to have the same number of electrons as one of the noble gases?


Correct

 

Explanation

 Mg is in group 2A so it has extra 2 valence electrons, by losing 2 losing electrons it can become stable as a noble gas.


    


 

Question 7

The magnesium ion formed in the previous question is isoelectronic with which noble gas?

 

Explanation

 If you remove 2 electrons from Mg then it has equal number of electrons to Ne

 

Question 8

How many electrons do the group 1A metals (alkali metals) lose to be isoelectronic with a noble gas?

Correct

 

Explanation

Group 1A elements are always = +1 (this means they lose 1 electron to be  electronic to a noble gas) 

 

Question 9

How many electrons do the group 7A elements (halogens) gain to be isoelectronic with a noble gas?

Correct

 

 According to the chart above Group 7A gain 1 electron because their charge is -1

 

Question 10

How many electrons are in a lithium atom, Li?

 

 

 Typically the number of electrons an atom has is equivalent to the number of protons an atom has (the exception to this rule are ions or unstable atoms but for all intensive purposes unless otherwise stated assume the atoms stability).
 

Question 11

How many electrons are in the S2- ion?

 

 Number of electron = atomic number + charge (additional electrons)

18 electron = 16 + 2

 

Question 12

How many electrons are in the calcium ion created by the calcium atom, Ca, losing 2 electrons?

Help: Ions defined

 

 Ca: Atomic Number = 20

If Ca loses 2 electrons then Ca has 18 electrons


 

Question 13

How many protons are in the phosphorous atom, P?
Correct

 

 Phosphorus Atomic Number : 15 (so there are 15 electrons/protons)

 

Question 14

Which element has 11 protons? 

Refer to the periodic table in the next question for this and the following questions.

 

Explanation

 

Question 15

What is the actual average mass of 1 Li atom (in grams/atom)? Express your answer in scientific notation to 3 SIG. FIG.

Help: Mass of an atom

Correct

 

Explanation

The mass of 1 Li atom:  1 atom x 6.94(g/mol) x (1 mol / 6.022E23 atom) = 1.15E-23g

 

Question 16

Which of the following elements are diatomic molecules at room temperature?
(All answers must be correct to get credit.) 

Help: Introduction to notation

Select one or more:
 Correct
 Correct
 Correct

 

Explanation

 

It forms a magic 7 (minus H because it's full of itself, but I guess most things are full of it so whatever).
 

Question 17

Write dinitrogen pentoxide using chemical symbols.

Help: Naming molecular compounds

 

Explanation

 Prefixes used in naming molecular compounds (compounds made from nonmetals).

1 mono- CO is carbon monoxide
2 di- SO2 is sulfur dioxide
3 tri-  SO3 is sulfur trioxide
4 tetra- CCl4 is carbon tetrachloride
5 penta-  PCl5 is phosphorus pentachloride
6 hexa- SF6 is sulfur hexafluoride

The ending of the second element is dropped and replaced with "ide".

 

Question 18

What is the name of the molecular compound ClF3? (Remember to leave a space between the two words.)

 

Explanation

 Look above!

 

Question 19

How many electrons does magnesium, Mg, need to lose to have the same number of electrons as one of the noble gases?

Help: Losing electrons

Help: Periodic Table showing charges

Correct

 

Explanation

 Atoms can only gain or lose a few electrons to be isoelectronic with a noble gas. 


Isoelectronic meaning that when compared both atoms have the same number of electrons.


Mg is closest to Ne, and in order to be isoelectronic it must lose 2 electrons.

 

Question 20

The magnesium ion formed in the previous question is isoelectronic with which noble gas?

 

Explanation

 Look above!

 

Question 21

How many electrons do the group 1A metals (alkali metals) lose to be isoelectronic with a noble gas?

Correct

 

Explanation

 Let's take for example Na (sodium) for it to be isoelectronic with a noble gas (specifically Ne) it must lose one electron.

 

Question 22

How many electrons do the group 7A elements (halogens) gain to be isoelectronic with a noble gas?

Correct

 

Explanation

  Lets take for example F (fluorine) for it to be isoelectronic with a noble gas (specifically Ne) it must gain one electron

 

Question 23

Which statements are correct about MgCl2? (All correct answers must be selected for credit.)

Help: Ionic compounds

Select one or more:
 Correct
 Correct
 Correct
 Correct

 

Explanation

Ionic compounds are all solids at room temperature. They consist of positive and negative ions held together by strong electrostatic forces. 


For example, NaCl consists of positive sodium ions (Na+) attracted to negative chloride ions (Cl-). NaCl is not a molecule, but consists of many sodium and chloride ions attracted to each other in the solid.

This is highly inconvenient, but if you zoom in you can see the charges on each individual atom.
 

Question 24

What is the name of KF?

Help: Naming ionic compounds

 

Explanation

 Ionic compounds (a metal and a nonmetal) are named using the name of the metal followed by the name of the nonmetal with its ending dropped and replaced with ide. 

Ex:
NaCl is sodium chloride,
MgCl2 is magnesium chloride, and
MgO is magnesium oxide.

 

Question 25

Write the composition of calcium iodide.

Sodium sulfide is Na2S. In Moodle, it is written Na2S.

Help: Using oxidation states to find composition

 

Explanation

 

 

Question 26

What is the composition of aluminum nitride?

 

Explanation

 Look above!

 

Question 27

What is the composition of aluminum oxide?

 

Explanation

 Look above!

 

Question 28

What is the composition of iron (II) sulfide? (Hint, given in feedback to answer.)

Help: Oxidation states and naming

 

Explanation

S is below O on the periodic table. So, like O, it gains 2 electrons to be isoelectronic with a noble gas.

 

Question 29

What is the formula for lead (IV) oxide? (Lead has 2 oxidation states.)

Help: Oxidation states and naming (review)

 

Explanation

S like O gains 2 electrons to be isoelectronic with a noble gas.

 

Question 30

What is the mass of one molecule of carbon monoxide, CO in u, amu, or atomic mass units? Use 4 SIG. FIG.

Help: Periodic table and mass

Correct

 

Explanation

 The number under the element symbol has 3 related meanings. The first 2 are: 

(1) It gives the relative average mass of the elements. For example, the Be atom (9.0122) is about 9 times the mass of the H atom (1.0079) and slightly less than half the mass of the F atom (18.9984). 

(2) It is the actual mass of the elements in atomic mass units (amu or simply u). 1 Carbon-12 (6 protons and 6 neutrons) atom is defined to be exactly 12 u. [The mass of C given in the periodic table is slightly larger because it is the average mass of all the C isotopes--same number or protons but different numbers of neutrons. Most C is carbon-12, but there is a small amount of carbon-14 (6 protons and 8 neutrons).] Examples, what are the masses of the following molecules to 4 significant figures in u?

The nitrogen molecule, N2: 2 x 14.00 u = 28.00 u
Carbon dioxide, CO2: 12.01 + 2 x 16.00 = 44.01 u

 

Question 31

What is the mass of one mole of CO in grams? Use 4 SIG. FIG.

Help: More on periodic table and mass

Correct

 

Explanation

 

 The number under the element symbol has a third meaning. This is the most common meaning. It is the mass in grams of 1 mole of the element. A mole is a number just like a dozen or a million. However, a mole is a very big number. It is 6.02 x 1023 (almost a trillion trillions or 1024). This number is called Avogadro's number. Thus, 1 mol of O atoms has a mass of 15.9994 g or 16.00 g to 4 significant figures. 


What is the mass of a mole (abbreviated mol) of the following molecules to 4 significant figures grams (g)?

Carbon dioxide- CO2: 12.01 + 2 x 16.00 = 44.01 g/mol (grams per mole)
Water- H2O: 2 x 1.008 + 16.00 = 18.02 g/mol

CO- 12.02 + 16 = 28.01

 

Question 32

What is the mass of one mole of ethane, C2H6 in grams?

Correct

 

Explanation

C2H6- 2(12.01) +6(1.008) = 30 g/mol

 

Question 33

What is the mass of one mole of ammonium chloride, NH4Cl, in grams?

Correct

 

Explanation

 NH4Cl = 14 + 4(1) +35

 

Question 34

What is the actual average mass of 1 Li atom (in grams/atom)? Express your answer in scientific notation to 3 SIG. FIG.

Help: Mass of an atom

Correct

 

Explanation

 1 carbon-12 atom is 12 u. 

1 mole carbon-12 is 12 g and a mole is 6.02214 x 1023. So, 1 carbon 12 atom has a mass of 12g/6.022 x 1023 = 1.993 x 10-23 g

The mass of 1 O2 molecules is 2x16/6.022 x 1023 = 5.31 x 10-23 g
1 u = 1g/6.02214x1023 = 1.66054 x 10-24 g

1 Li = 6.941/  6.022 x 1023 =1.15e-23

 

Question 35

Write the chemical formula for iron (II) chloride. (For Moodle, water is written H2O.)

Help: Chemical formula examples

 

Explanation

 Iron (II) = Fe 2+

Chloride= Cl- 


FeCl2 (charges have to balance out)

2+ + 2(1-)=0

 

Question 36

Write the chemical formula for iron (II) carbonate.

Help: Polyatomic ions and charges

 

Explanation

(II) tells you that Iron has a 2+ charge.


Ammonium ion: NH4+
Nitrate ion: NO3-
Sulfate ion: SO42- ; Hydrogen sulfate ion: HSO4-
Hydroxide ion: OH-
Cyanide ion: CN-
Phosphate ion: PO43-; Hydrogen phosphate ion: HPO42-; Dihydrogen phosphate ion: H2PO4-
Carbonate ion: CO32-; Hydrogen carbonate ion: HCO3-
Acetate ion: CH3COO-
Permanganate ion: MnO4-
Oxide ion: O2- (not polyatomic ion); Peroxide ion: O22-

 

Question 37

Write the chemical formula for iron (III) carbonate. For Moodle, magnesium hydrogen sulfate is written Mg(HSO4)2 meaning Mg(HSO4)2.

 

Explanation

 (III) tells you that Fe has a 3+ charge

Carbonate ion: CO32-

 

Question 38

Write the chemical formula for barium hydroxide.

 

Explanation

Hint, what charge do all barium ions have?

The answer is 2+.
Hydroxide ion: OH-

 

Question 39

Write the chemical formula for ammonium sulfate.

 

Explanation

Ammonium ion: NH4+

Sulfate ion: SO42-