Multiple questions, brainliest and 98 points to whoever answers all questions correctly

Question 1

The average atomic  mass  of element  is  84.66

calculation

Average  atomic mass is  of an element is the sum of masses of its isotope each  multiplied by its  natural  abundance.

that  is.

[(50.50 x  83.75) /100]   + [( 30.25 x 84.45)/100] + [(,9.25 x 87.40)/100]

=  42.29  +25.55 +16.82=  84.66

Question 2

fill the table

symbol    element    protons    neutrons   Electrons   mass No    Atomic No

Cs-133    cesium         55              78            55               133                55

Na-23      sodium         11                12            11                  23                  11

Ne 22       Neon           10              12            1 0                  22                  10        

Au -197     Gold            79             118            79                197                  79

Question 3

The moles of tungsten   that are  in  93.50  grams are 0.509  moles

moles=  mass/molar mass

 molar mass  of  tungsten  = 183.84 g/mol

moles  is therefore=  93.50  g/ 183.84  g/mol=  0.509  moles

question  4

CO2  molecules at STP  are 1.547 x10^23  molecules

 Step  1:  find the  moles of CO2

At  STP    1 mole of a gas= 22.4 l

                                    ?  =5.75 L

by cross multiplication

=  (5.75 L x 1 mole)/ 22.4 L= 0.257 moles

Step 2:  use the Avogadro's constant  to calculate the number of molecule

that is  1  moles = 6.02 x10^23 molecules

         0.257 moles= ? molecules

by  cross  multiplication

=(0.257 moles x 6.02  x 10^23) / 1 mole  = 1.547 x10^23  molecules

question 5

The number of calcium  atoms  is 3.82 x10^24  atoms

Step 1:  find the moles  of   calcium

= 253.50 g /40 g/mol= 6.34  moles

Step 2:  use the Avogadro's  law  to calculate the number of atoms.

that is   1 mole= 6.02 x 10^23 atoms

             6.34  moles=  ?  atoms

=6.34 x 6.02 x10^23  = 3.82  x10^24 atoms

Question   6

mass  in grams  of  NiBr2   is   126.97  grams

Step  1:  by use of  Avogadro's  law  constant  calculate  the  number  of moles

that  is  1 mole = 6.02 x 10^23

                 ?   =   3.50 x  10^23

by  cross  multiplication

= (1  mole  x 3.50  x10^23) /  6.02  x10^23 =0.581 moles

step 2:  calculate the  mass

mass =moles  x  molar mass

=  0.581 moles  x218.53 g/mol = 126.97 grams

 Bonus question

The molecules of water=  1.00  x10^26 molecules

  calculation

convert liters into  ml

= 3 x 1000  =  3000 ml

find the mass of  water

=  density  x volume

=3000  x0.998  2994  grams

find  the moles of water=mass/molar  mass

= 2994  g/  18  g/mol= 166.33 moles

Use  Avogadro's constant  to  calculate the molecules  of water

that is  1 mole=  6.02 x10^23  molecules

         166.33 moles= ? molecules

= (166.33 moles x6.02 x10^23 molecules) / 1 mole  =  1.00  x10^26  molecules

1

The average atomic  mass  of element  is  84.66

2

symbol    element    protons    neutrons   Electrons   mass No    Atomic No

Cs-133    cesium         55              78            55               133                55

Na-23      sodium         11                12            11                  23                  11

Ne 22       Neon           10              12            1 0                  22                  10        

Au -197     Gold            79             118            79                197                  79

3

The moles of tungsten   that are  in  93.50  grams are  0.509  moles

4

CO2  molecules at STP  are  1.547 x10^23  molecules

 Step  1:  find the  moles of CO2

At  STP    1 mole of a gas= 22.4 l

                                    ?  =5.75 L

all ik

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

that's it!

if you need further assistance, let me know: )

~ trueboss72