To gain an idea as to how many atoms are in a gram or so of copper, use the larger balance
on the right. Press Add atoms to put a scoop of atoms in the weighing dish, and keep
adding until the balance registers between 1 and 2 grams. If you don't seem to be making
much progress, adjust the exponent using the slider, which will make the scoop size bigger.
How many atoms did you need to add?

Mole is unit that is used to measure the smaller particles such as ions, atoms and molecules.   There are atoms are present in the 2 g of Copper.

Mole:

Mole is unit that is used to measure the smaller particles such as ions, atoms and molecules.  One mole is equal to the Avogadro's constant.

The formula foe number of mole,

Where,

n - number of moles = 0.03 mole

w - mass of molecule

m - molar mass of the copper = 63.54 g/mol

The number of atoms in the 0.03 moles.

Therefore, there are atoms are present in the 2 g of Copper.

To know more about moles, refer to the link:

link

Explanation:

To solve this problem, we must understand the relationship between mass of a substance and the number of atoms.

Atoms are the smallest indivisible particles of any matter. A substance can be made up of several number of atoms in their space.

The mass of any substance is a function of the amount of atoms its contains.

The mass of a substance is related in chemistry to the amount of atoms its contains using the parameter called the number of moles.

A mole is the amount of substance that contains the Avogadro's number of particles. This number is 6.02  x 10²³ particles. The particles here can be protons, neutrons, electrons, atoms e.t.c.

Now,

             Number of moles  =

          Molar mass of copper  = 63.6g/mole

         Number of moles  =  = 0.03mole

Since 1 mole of a substance contains  6.02  x 10²³atoms

        0.03 mole of copper will contain 0.03 x  6.02  x 10²³atoms

                                                    = 1.89 x 10²² atoms

He needs to add 1.89 x 10²² atoms to make 2g of the sample.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.